Related
I'm trying to load a sub view on to every single page of my app from a nib file. Right now I'm using a somewhat unusual approach to loading this sub view in that I am doing it through an extension of UIStoryboard (probably not relevant to my problem, but I'm not sure). So this is how the code looks when I load the nib file:
extension UIStoryboard {
public func appendCustomView(to viewController: UIViewController) {
if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview {
viewController.view.addSubview(myCustomSubview)
}
}
}
This code does what it's supposed to do and adds "MyCustomSubview" to the view controller (I won't go in to detail on exactly how this method gets called because it works so it doesn't seem important). The problem is I can't for the life of me figure out how to add constraints that effect the size of myCustomSubview. I have tried putting code in the function I showed above as well as in the MyCustomSubview swift file to add constraints but no matter what I do the subview never changes.
Ideally the constraints would pin "MyCustomSubview" to the bottom of the ViewController, with width set to the size of the screen and a hard coded height constraint.
Here are the two main methods I tried (with about 100 minor variations for each) that did NOT work:
Method 1 - Add constraint directly from "appendCustomView"
public func appendCustomView(to viewController: UIViewController) {
if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview {
let top = NSLayoutConstraint(item: myCustomSubview, attribute: .top, relatedBy: .equal
, toItem: viewController.view, attribute: .top, multiplier: 1, constant: 50.0)
viewController.view.addSubview(myCustomSubview)
viewController.view.addConstraint(top)
}
}
Method 2 - Add constraint outlets and setter method in MyCustomSubview
class MyCustomSubview: UIView {
#IBOutlet weak var widthConstraint: NSLayoutConstraint!
#IBOutlet weak var heightConstraint: NSLayoutConstraint!
func setConstraints(){
self.widthConstraint.constant = UIScreen.main.bounds.size.width
self.heightConstraint.constant = 20
}
}
And call setter method in "appendCustomView"
public func appendCustomView(to viewController: UIViewController) {
if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview {
myCustomSubview.setConstraints()
viewController.view.addSubview(myCustomSubview)
}
}
(*note: the actual constraints of these examples are irrelevant and I wasn't trying to meet the specs I mentioned above, I was just trying to make any sort of change to the view to know that the constraints were updating. They weren't.)
Edit : Changed "MyCustomNib" to "MyCustomSubview" for clarity.
When you add constraints onto a view from a Nib, you have to call yourView.translatesAutoresizingMaskIntoConstraints = false, and you also need to make sure that you have all 4 (unless it's a label or a few other view types which only need 2) constraints in place:
Here's some sample code that makes a view fill it's parent view:
parentView.addSubview(yourView)
yourView.translatesAutoresizingMaskIntoConstraints = false
yourView.topAnchor.constraint(equalTo: parentView.topAnchor).isActive = true
yourView.leadingAnchor.constraint(equalTo: parentView.leadingAnchor).isActive = true
yourView.bottomAnchor.constraint(equalTo: parentView.bottomAnchor).isActive = true
yourView.trailingAnchor.constraint(equalTo: parentView.trailingAnchor).isActive = true
Edit: I've actually come around to perferring this method of adding NSLayoutConstraints, even though the results are the same
NSLayoutConstraint.activate([
yourView.topAnchor.constraint(equalTo: parentView.topAnchor),
yourView.leadingAnchor.constraint(equalTo: parentView.leadingAnchor),
yourView.bottomAnchor.constraint(equalTo: parentView.bottomAnchor),
yourView.trailingAnchor.constraint(equalTo: parentView.trailingAnchor),
])
For anyone who comes across this in the future, this is the solution I came up with by tweaking this answer a little bit
Add a setConstraints(withRelationshipTo) method in the swift class that corresponds to the nib file:
class MyCustomSubview: UIView {
func setConstraints(withRelationshipTo view: UIView){
self.translatesAutoresizingMaskIntoConstraints = false
// Replace with your own custom constraints
self.heightAnchor.constraint(equalToConstant: 40.0).isActive = true
self.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
self.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
self.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
}
}
Then call the setConstraints method after you add the nib file to the view (probably in viewWillAppear or viewDidLoad of a view controller )
class MyViewController: UIViewController {
override func viewWillAppear(_ animated: Bool){
super.viewWillAppear(animated)
if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview {
let view = self.view // Added for clarity
view.addSubview(myCustomSubview)
myCustomSubview.setConstraints(withRelationshipTo: view)
}
}
}
You can use this extension for anywhere you're going to add a subview to a existing UIView.
extension UIView {
func setConstraintsFor(contentView: UIView, left: Bool = true, top: Bool = true, right: Bool = true, bottom: Bool = true) {
contentView.translatesAutoresizingMaskIntoConstraints = false
self.addSubview(contentView)
var constraints : [NSLayoutConstraint] = []
if left {
let constraintLeft = NSLayoutConstraint(item: contentView, attribute: .left, relatedBy: .equal, toItem: self, attribute: .left, multiplier: 1, constant: 0)
constraints.append(constraintLeft)
}
if top {
let constraintTop = NSLayoutConstraint(item: contentView, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1, constant: 0)
constraints.append(constraintTop)
}
if right {
let constraintRight = NSLayoutConstraint(item: contentView, attribute: .right, relatedBy: .equal, toItem: self, attribute: .right, multiplier: 1, constant: 0)
constraints.append(constraintRight)
}
if bottom {
let constraintBottom = NSLayoutConstraint(item: contentView, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1, constant: 0)
constraints.append(constraintBottom)
}
self.addConstraints(constraints)
}
}
You can call this method like this:
containerView.setConstraintsFor(contentView: subView!, top: false)
This will add subView to the containerView and constraint to all sides except top side.
You can modify this method to pass left, top, right, bottom Constant value if you want.
Historic question alert:
Note that 15 years later, you can now simply
yourConstraint.setValue(0.75, forKey: "multiplier")
original QA:
I created two views in one superview, and then added constraints between views:
_indicatorConstrainWidth = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeWidth multiplier:1.0f constant:0.0f];
[_indicatorConstrainWidth setPriority:UILayoutPriorityDefaultLow];
_indicatorConstrainHeight = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeHeight multiplier:1.0f constant:0.0f];
[_indicatorConstrainHeight setPriority:UILayoutPriorityDefaultLow];
[self addConstraint:_indicatorConstrainWidth];
[self addConstraint:_indicatorConstrainHeight];
Now I want to change multiplier property with animation, but I can't figure out how to change the multipler property. (I found _coefficient in private property in header file NSLayoutConstraint.h, but it private.)
How do I change multipler property?
My workaround is to remove the old constraint and add the new one with a different value for multipler.
Here is an NSLayoutConstraint extension in Swift that makes setting a new multiplier pretty easy:
In Swift 3.0+
import UIKit
extension NSLayoutConstraint {
/**
Change multiplier constraint
- parameter multiplier: CGFloat
- returns: NSLayoutConstraint
*/
func setMultiplier(multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
Demo usage:
#IBOutlet weak var myDemoConstraint:NSLayoutConstraint!
override func viewDidLoad() {
let newMultiplier:CGFloat = 0.80
myDemoConstraint = myDemoConstraint.setMultiplier(newMultiplier)
//If later in view lifecycle, you may need to call view.layoutIfNeeded()
}
If you have only have two sets of multipliers that need to be applied, from iOS8 onwards you can add both sets of constraints and decide which should be active at any time:
NSLayoutConstraint *standardConstraint, *zoomedConstraint;
// ...
// switch between constraints
standardConstraint.active = NO; // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.active = YES;
[self.view layoutIfNeeded]; // or using [UIView animate ...]
Swift 5.0 version
var standardConstraint: NSLayoutConstraint!
var zoomedConstraint: NSLayoutConstraint!
// ...
// switch between constraints
standardConstraint.isActive = false // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.isActive = true
self.view.layoutIfNeeded() // or using UIView.animate
The multiplier property is read only. You have to remove the old NSLayoutConstraint and replace it with a new one to modify it.
However, since you know you want to change the multiplier, you can just change the constant by multiplying it yourself when changes are needed which is often less code.
A helper function I use to change multiplier of an existing layout constraint. It creates and activates a new constraint and deactivates the old one.
struct MyConstraint {
static func changeMultiplier(_ constraint: NSLayoutConstraint, multiplier: CGFloat) -> NSLayoutConstraint {
let newConstraint = NSLayoutConstraint(
item: constraint.firstItem,
attribute: constraint.firstAttribute,
relatedBy: constraint.relation,
toItem: constraint.secondItem,
attribute: constraint.secondAttribute,
multiplier: multiplier,
constant: constraint.constant)
newConstraint.priority = constraint.priority
NSLayoutConstraint.deactivate([constraint])
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
Usage, changing multiplier to 1.2:
constraint = MyConstraint.changeMultiplier(constraint, multiplier: 1.2)
Objective-C Version for Andrew Schreiber answer
Create the category for NSLayoutConstraint Class and add the method in .h file like this
#import <UIKit/UIKit.h>
#interface NSLayoutConstraint (Multiplier)
-(instancetype)updateMultiplier:(CGFloat)multiplier;
#end
In the .m file
#import "NSLayoutConstraint+Multiplier.h"
#implementation NSLayoutConstraint (Multiplier)
-(instancetype)updateMultiplier:(CGFloat)multiplier {
[NSLayoutConstraint deactivateConstraints:[NSArray arrayWithObjects:self, nil]];
NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:self.firstItem attribute:self.firstAttribute relatedBy:self.relation toItem:self.secondItem attribute:self.secondAttribute multiplier:multiplier constant:self.constant];
[newConstraint setPriority:self.priority];
newConstraint.shouldBeArchived = self.shouldBeArchived;
newConstraint.identifier = self.identifier;
newConstraint.active = true;
[NSLayoutConstraint activateConstraints:[NSArray arrayWithObjects:newConstraint, nil]];
//NSLayoutConstraint.activateConstraints([newConstraint])
return newConstraint;
}
#end
Later in the ViewController create the outlet for the constraint you want to update.
#property (strong, nonatomic) IBOutlet NSLayoutConstraint *topConstraint;
and update the multiplier where ever you want like below..
self.topConstraint = [self.topConstraint updateMultiplier:0.9099];
You can change the "constant" property instead to achieve the same goal with a little math. Assume your default multiplier on the constraint is 1.0f. This is Xamarin C# code which can be easily translated to objective-c
private void SetMultiplier(nfloat multiplier)
{
FirstItemWidthConstraint.Constant = -secondItem.Frame.Width * (1.0f - multiplier);
}
As is in other answers explained: You need to remove constraint and create new one.
You can avoid returning new constraint by creating static method for NSLayoutConstraint with inout parameter, which allows you to reassign passed constraint
import UIKit
extension NSLayoutConstraint {
static func setMultiplier(_ multiplier: CGFloat, of constraint: inout NSLayoutConstraint) {
NSLayoutConstraint.deactivate([constraint])
let newConstraint = NSLayoutConstraint(item: constraint.firstItem, attribute: constraint.firstAttribute, relatedBy: constraint.relation, toItem: constraint.secondItem, attribute: constraint.secondAttribute, multiplier: multiplier, constant: constraint.constant)
newConstraint.priority = constraint.priority
newConstraint.shouldBeArchived = constraint.shouldBeArchived
newConstraint.identifier = constraint.identifier
NSLayoutConstraint.activate([newConstraint])
constraint = newConstraint
}
}
Example usage:
#IBOutlet weak var constraint: NSLayoutConstraint!
override func viewDidLoad() {
NSLayoutConstraint.setMultiplier(0.8, of: &constraint)
// view.layoutIfNeeded()
}
in Swift 5.x you can use:
extension NSLayoutConstraint {
func setMultiplier(multiplier: CGFloat) -> NSLayoutConstraint {
guard let firstItem = firstItem else {
return self
}
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(item: firstItem, attribute: firstAttribute, relatedBy: relation, toItem: secondItem, attribute: secondAttribute, multiplier: multiplier, constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
NONE OF THE ABOVE CODE WORKED FOR ME
SO AFTER TRYING TO MODIFY MY OWN CODE THIS CODE
This code is working in Xcode 10 and swift 4.2
import UIKit
extension NSLayoutConstraint {
/**
Change multiplier constraint
- parameter multiplier: CGFloat
- returns: NSLayoutConstraintfor
*/i
func setMultiplier(multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
#IBOutlet weak var myDemoConstraint:NSLayoutConstraint!
override func viewDidLoad() {
let newMultiplier:CGFloat = 0.80
myDemoConstraint = myDemoConstraint.setMultiplier(newMultiplier)
//If later in view lifecycle, you may need to call view.layoutIfNeeded()
}
Swift 5+
Based on Evgenii's answer, here is an elegant way to change the multiplier through extension.
extension NSLayoutConstraint {
func change(multiplier: CGFloat) {
let newConstraint = NSLayoutConstraint(item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = self.priority
NSLayoutConstraint.deactivate([self])
NSLayoutConstraint.activate([newConstraint])
}
}
And the usage:
myConstraint.change(multiplier: 0.6)
Yes w can change multiplier values just make an extension of NSLayoutConstraint
and use it like ->
func setMultiplier(_ multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem!,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = shouldBeArchived
newConstraint.identifier = identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
self.mainImageViewHeightMultiplier = self.mainImageViewHeightMultiplier.setMultiplier(375.0/812.0)
Simple answer, no extensions required. I tried for my case, worked fine for me.
So as multiplier is a get only property, we can simply set multiplier in the following way :
yourConstraintOutlet.setValue(yourDesiredMultiplierValue, forKey: "multiplier")
yourConstraintOutlet.setValue(0.75, forKey: "multiplier")
Switch by changing the active constraint in code as suggested by many other answers did not work for me. So i created 2 constrains, one installed and the other not, bind both to the code, and then switch by removing one and adding the other.
For the sake of completeness, to bind the constrain drag the constrain to the code using mouse right button, just like any other graphic element:
I named one proportionIPad and the other proportionIPhone.
Then, add the following code, at viewDidLoad
override open func viewDidLoad() {
super.viewDidLoad()
if ... {
view.removeConstraint(proportionIphone)
view.addConstraint(proportionIpad)
}
}
I am using xCode 10 and swift 5.0
Here is an answer based on #Tianfu's answer in C#. Other answers that require activation and deactivation of constraints did not work for me.
var isMapZoomed = false
#IBAction func didTapMapZoom(_ sender: UIButton) {
let offset = -1.0*graphHeightConstraint.secondItem!.frame.height*(1.0 - graphHeightConstraint.multiplier)
graphHeightConstraint.constant = (isMapZoomed) ? offset : 0.0
isMapZoomed = !isMapZoomed
self.view.layoutIfNeeded()
}
#IBOutlet weak var viewHeightConstraint: NSLayoutConstraint!
let heightOfSuperview = self.view.bounds.height
viewHeightConstraint.constant = heightOfSuperview * 0.5
// this has the same effect as multiplier
I have a way. No need to re-create a constraint.
Assuming you have an imageView which you want to constraint its aspect ratio to match the image aspect ratio.
Create an aspect ratio constraint for the imageView and set multiplier to 1 and constant to 0.
Create an outlet for the aspect ratio constraint.
Change the constraint constant value at runtime, according the the image you load:
let multiplier = image.size.width / image.size.height
let (w, h) = (imageView.bounds.width, imageView.bounds.height)
let expectedW = h * multiplier
let diff = expectedW - h
imageViewAspectConstraint.constant = image.size.width >= image.size.height ? diff : -diff // multiplier is read-only, but constant is RW
note that you can simply yourConstraint.setValue(0.75, forKey: "multiplier")
or
Xcode 13.3.1, Swift 5.6 (swiftlang-5.6.0.323.62 clang-1316.0.20.8)
This is based on #Ullas Pujary's answer and I make it a little swifter and remove the warnings on firstItemandsecondItem`
extension NSLayoutConstraint {
public static func setMultiplier(_ newMultiplier: CGFloat, of constraint: inout NSLayoutConstraint) {
constraint.isActive = false
guard
let firstItem = constraint.firstItem,
let secondItem = constraint.secondItem
else {
return
}
let newConstraint = NSLayoutConstraint(item: firstItem,
attribute: constraint.firstAttribute,
relatedBy: constraint.relation,
toItem: secondItem,
attribute: constraint.secondAttribute,
multiplier: newMultiplier,
constant: constraint.constant)
newConstraint.priority = constraint.priority
newConstraint.shouldBeArchived = constraint.shouldBeArchived
newConstraint.identifier = constraint.identifier
newConstraint.isActive = true
constraint = newConstraint
}
}
One can read:
var multiplier: CGFloat
The multiplier applied to the second attribute participating in the constraint.
on this documentation page. Doesn't that mean that one should be able to modify multiplier (since it is a var)?
I'm trying to make a UIView image for my background in swift using pattern image. The code I have works well except for the fact that I want the image to take the whole screen. My code looks like this: self.view.backgroundColor = UIColor(patternImage: UIImage(named: "backgroundImage")!)
Does anyone know how to make the background an image that will take up the whole screen, and would scale when appearing on different iPhone screen sizes?
Note That:
I posted this answer from my old account (which is deprecated for me and I can't access it anymore), this is my improved answer.
You can do it programmatically instead of creating an IBOutlet in each view.
just create a UIView extension (File -> New -> File -> Swift File -> name it whatever you want) and add:
extension UIView {
func addBackground() {
// screen width and height:
let width = UIScreen.mainScreen().bounds.size.width
let height = UIScreen.mainScreen().bounds.size.height
let imageViewBackground = UIImageView(frame: CGRectMake(0, 0, width, height))
imageViewBackground.image = UIImage(named: "YOUR IMAGE NAME GOES HERE")
// you can change the content mode:
imageViewBackground.contentMode = UIViewContentMode.ScaleAspectFill
self.addSubview(imageViewBackground)
self.sendSubviewToBack(imageViewBackground)
}}
Now, you can use this method with your views, for example:
override func viewDidLoad() {
super.viewDidLoad()
self.view.addBackground()
}
Just add your UIImageView positioned
centered and with all edges snapping to the edges. Leave it there and
click on the right bottom corner as shown below and now go ahead and
add 4 constrains to Top, Bottom, Left and Right Edges.
Now just select your image view and using the IB inspector select how
you would like your image: fill or fit as you can see as follow:
This is the updated answer of my previous one.
As the same approach of my previous answer, You can create an extension of UIView and add addBackground() method to it, as follows:
Remember: if you are adding it in a new .swift file, remember to add import UIKit
extension UIView {
func addBackground(imageName: String = "YOUR DEFAULT IMAGE NAME", contentMode: UIView.ContentMode = .scaleToFill) {
// setup the UIImageView
let backgroundImageView = UIImageView(frame: UIScreen.main.bounds)
backgroundImageView.image = UIImage(named: imageName)
backgroundImageView.contentMode = contentMode
backgroundImageView.translatesAutoresizingMaskIntoConstraints = false
addSubview(backgroundImageView)
sendSubviewToBack(backgroundImageView)
// adding NSLayoutConstraints
let leadingConstraint = NSLayoutConstraint(item: backgroundImageView, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 0.0)
let trailingConstraint = NSLayoutConstraint(item: backgroundImageView, attribute: .trailing, relatedBy: .equal, toItem: self, attribute: .trailing, multiplier: 1.0, constant: 0.0)
let topConstraint = NSLayoutConstraint(item: backgroundImageView, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1.0, constant: 0.0)
let bottomConstraint = NSLayoutConstraint(item: backgroundImageView, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1.0, constant: 0.0)
NSLayoutConstraint.activate([leadingConstraint, trailingConstraint, topConstraint, bottomConstraint])
}
}
Note that the updates for this answer are:
Swift 4 code 🙂
Adding -programatically- NSLayoutConstraints: that's because when applying what's mentioned in my previous answer, it works fine for the current device orientation, but not when the application does support both portrait/landscape modes, if the device orientation has been changed, the background imageView size will be the same (same size) and not adapts the new width/height of the device screen, so adding constraints should solve this issue.
Adding default parameters: for more flexibility, you might -sometimes- want to change the default image or even the context mode for you background:
Usage:
Assuming that you want to call it in viewDidLoad():
override func viewDidLoad() {
//...
// you can call 4 versions of addBackground() method
// 1- this will add it with the default imageName and default contextMode
view.addBackground()
// 2- this will add it with the edited imageName and default contextMode
view.addBackground(imageName: "NEW IMAGE NAME")
// 3- this will add it with the default imageName and edited contextMode
view.addBackground(contentMode: .scaleAspectFit)
// 4- this will add it with the default imageName and edited contextMode
view.addBackground(imageName: "NEW IMAGE NAME", contextMode: .scaleAspectFit)
}
Here are your options for scaling!
For the .contentMode property:
ScaleToFill
This will scale the image inside the image view to fill the entire boundaries of the image view.
ScaleAspectFit
This will make sure the image inside the image view will have the right aspect ratio and fit inside the image view’s boundaries.
ScaleAspectFill
This will make sure the image inside the image view will have the right aspect ratio and fill the entire boundaries of the image view.
For this value to work properly, make sure that you have set the clipsToBounds property of the imageview to true.
class SecondViewController : UIViewController {
let backgroundImage = UIImage(named: "centralPark")
var imageView: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
self.thirdChoiceField.delegate = self
self.datePicker.minimumDate = NSDate()
imageView = UIImageView(frame: view.bounds)
imageView.contentMode = .ScaleAspectFill
imageView.clipsToBounds = true
imageView.image = backgroundImage
imageView.center = view.center
view.addSubview(imageView)
self.view.sendSubviewToBack(imageView)
me showing my answer as which Lines of code helps me...
extension file code ....
extension UIView {
func addBackground() {
let width = UIScreen.main.bounds.size.width
let height = UIScreen.main.bounds.size.height
let imageViewBackground = UIImageView(frame: CGRect(x: 0, y: 0, width: width, height: height))
imageViewBackground.image = UIImage(named: "Your Background Image Name")
imageViewBackground.contentMode = .scaleAspectFill
self.addSubview(imageViewBackground)
self.sendSubviewToBack(imageViewBackground)
}
}
and in view controller file....
override func viewDidLoad() {
super.viewDidLoad()
view.addBackground()
}
Thank You Guys !
Ahmad Fayyas Solution in Swift 3.0:
func addBackground() {
let width = UIScreen.main.bounds.size.width
let height = UIScreen.main.bounds.size.height
let imageViewBackground = UIImageView(frame: CGRect(x:0, y:0, width: width, height: height))
imageViewBackground.image = UIImage(named: "YOUR IMAGE NAME GOES HERE")
// you can change the content mode:
imageViewBackground.contentMode = UIViewContentMode.scaleAspectFill
self.view.addSubview(imageViewBackground)
self.view.sendSubview(toBack: imageViewBackground)
}
This uses PureLayout. You could just use AutoLayout with a few more lines.
UIImageView* imgView = UIImageView(image: myUIImage)
imgView.setTranslatesAutoresizingMaskIntoConstraints(false)
self.view.addSubview(imgView)
self.view.addConstraints(imgView.autoPinEdgesToSuperviewEdgesWithInsets(UIEdgeInsetsMake(0,0,0,0))
I used constraints to make the image "autoLayout". I made a view to show an activity indicator (with full background image), while the view on segue is loading. The code is as follows.
var containerView: UIView = UIView()
var actionIndicator: UIActivityIndicatorView = UIActivityIndicatorView()
private func showActivityIndicator() {
///first I set the containerView and the background image
containerView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(containerView)
adjustConstFullSize(containerView, parentView: self.view)
let backImage = UIImageView(image: UIImage(named: "AppBackImage"))
backImage.contentMode = UIViewContentMode.ScaleAspectFill
backImage.translatesAutoresizingMaskIntoConstraints = false
containerView.addSubview(backImage)
adjustConstFullSize(backImage, parentView: containerView)
////setting the spinner (activity indicator)
actionIndicator.frame = CGRectMake(0.0, 0.0, 40.0, 40.0)
actionIndicator.center = CGPointMake(containerView.bounds.size.width / 2, containerView.bounds.size.height / 2)
actionIndicator.hidesWhenStopped = true
actionIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.WhiteLarge
containerView.insertSubview(actionIndicator, aboveSubview: backImage)
///throw the container to the main view
view.addSubview(containerView)
actionIndicator.startAnimating()
}
This is the code for the "adjustConstFullSize" function.
func adjustConstFullSize(adjustedView: UIView!, parentView: UIView!) {
let topConstraint = NSLayoutConstraint(item: adjustedView,
attribute: .Top,
relatedBy: .Equal,
toItem: parentView,
attribute: .Top,
multiplier: 1.0,
constant: 0.0)
let leftConstraint = NSLayoutConstraint(item: adjustedView,
attribute: .Leading,
relatedBy: .Equal,
toItem: parentView,
attribute: .Leading,
multiplier: 1.0,
constant: 0.0)
let rightConstraint = NSLayoutConstraint(item: adjustedView,
attribute: .Trailing,
relatedBy: .Equal,
toItem: parentView,
attribute: .Trailing,
multiplier: 1.0,
constant: 0.0)
let bottomConstraint = NSLayoutConstraint(item: adjustedView,
attribute: .Bottom,
relatedBy: .Equal,
toItem: parentView,
attribute: .Bottom,
multiplier: 1.0,
constant: 0.0)
parentView.addConstraints([topConstraint, leftConstraint, rightConstraint, bottomConstraint])
}
In the function shown above, I "tied" the containerView constraints to the main view constraints, making the view "full size". I did the same for the UIImageView and also set the contentMode to AspectFill - this is crucial, because we want the image to fill the content without stretching.
To remove the view, after the lazy loading, just use the code below.
private func hideActivityIndicator() {
actionIndicator.stopAnimating()
containerView.removeFromSuperview()
}
For this, I think you'll need to create a UIImageView that is pinned to the parent views top / bottom / left / right. This will make the UIImageView always the match the size of the display. Just make sure you set the content mode on the imageview to be AspectFit
var newImgThumb : UIImageView
newImgThumb = UIImageView(view.bounds)
newImgThumb.contentMode = .ScaleAspectFit
view.addSubview(newImgThumb)
//Don't forget this line
newImgThumb.setTranslatesAutoresizingMaskIntoConstraints(false)
NSDictionary *views =NSDictionaryOfVariableBindings(newImgThumb);
// imageview fills the width of its superview
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"|[newImgThumb]|" options:0 metrics:metrics views:views]];
// imageview fills the height of its superview
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[newImgThumb]|" options:0 metrics:metrics views:views]];
`
CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat screenWidth = screenRect.size.width;
CGFloat screenHeight = screenRect.size.height;
_imgBackGround.frame = CGRectMake(0, 0, screenWidth, screenHeight);`
TL;DR
My programmatically created table view cells are not resizing according to the intrinsic content height of their custom views, even though I am using UITableViewAutomaticDimension and setting both the top and bottom constraints.
The problem probably lies in my implementation of the UITableViewCell subclass. See the code below under Doesn't work programmatically > Code > MyCustomCell.swift.
Goal
I'm trying to make a suggestion bar for a custom Mongolian keyboard. Mongolian is written vertically. In Android it looks like this:
Progress
I've learned that I should use a UITableView with variable cell heights, which is available starting with iOS 8. This requires using auto layout and telling the table view to use automatic dimensions for the cell heights.
Some things I've had to learn along the way are represented in my recent SO questions and answers:
How to make a custom table view cell
Getting variable height to work with in a table view with a standard UILabel
Getting intrinsic content size to work for a custom view
Using a programmatically created UITableViewCell
Set constraints programmatically
So I have come to the point where I have the vertical labels that support intrinsic content size. These labels go in my custom table view cells. And as described in the next section, they work when I do it in the storyboard, but not when I create everything programmatically.
Works in IB
In order to isolate the problem I created two basic projects: one for where I use the storyboard and one where I do everything programmatically. The storyboard project works. As can be seen in the following image, each table view cell resizes to match the height of custom vertical label.
In IB
I set constraints to pin the top and bottom as well as centering the label.
Code
ViewController.swift
import UIKit
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
let myStrings: [String] = ["a", "bbbbbbb", "cccc", "dddddddddd", "ee"]
let cellReuseIdentifier = "cell"
#IBOutlet var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
tableView.estimatedRowHeight = 44.0
tableView.rowHeight = UITableViewAutomaticDimension
}
// number of rows in table view
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.myStrings.count
}
// create a cell for each table view row
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell:MyCustomCell = self.tableView.dequeueReusableCellWithIdentifier(cellReuseIdentifier) as! MyCustomCell
cell.myCellLabel.text = self.myStrings[indexPath.row]
return cell
}
// method to run when table view cell is tapped
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
print("You tapped cell number \(indexPath.row).")
}
}
MyCustomCell.swift
import UIKit
class MyCustomCell: UITableViewCell {
#IBOutlet weak var myCellLabel: UIMongolSingleLineLabel!
}
Doesn't work programmatically
Since I want the suggestion bar to be a part of the final keyboard, I need to be able to create it programmatically. However, when I try to recreate the above example project programmatically, it isn't working. I get the following result.
The cell heights are not resizing and the custom vertical labels are overlapping each other.
I also get the following error:
Warning once only: Detected a case where constraints ambiguously
suggest a height of zero for a tableview cell's content view. We're
considering the collapse unintentional and using standard height
instead.
This error has been brought up before multiple times on Stack Overflow:
iOS8 - constraints ambiguously suggest a height of zero
Detected a case where constraints ambiguously suggest a height of zero
custom UITableviewcell height not set correctly
ios 8 (UITableViewCell) : Constraints ambiguously suggest a height of zero for a tableview cell's content view
However, the problem for most of those people is that they were not setting both a top and bottom pin constraint. I am, or at least I think I am, as is shown in my code below.
Code
ViewController.swift
import UIKit
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
let myStrings: [String] = ["a", "bbbbbbb", "cccc", "dddddddddd", "ee"]
let cellReuseIdentifier = "cell"
var tableView = UITableView()
override func viewDidLoad() {
super.viewDidLoad()
// Suggestion bar
tableView.frame = CGRect(x: 0, y: 20, width: view.bounds.width, height: view.bounds.height)
tableView.registerClass(MyCustomCell.self, forCellReuseIdentifier: cellReuseIdentifier)
tableView.delegate = self
tableView.dataSource = self
tableView.estimatedRowHeight = 44.0
tableView.rowHeight = UITableViewAutomaticDimension
view.addSubview(tableView)
}
// number of rows in table view
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.myStrings.count
}
// create a cell for each table view row
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell:MyCustomCell = self.tableView.dequeueReusableCellWithIdentifier(cellReuseIdentifier) as! MyCustomCell
cell.myCellLabel.text = self.myStrings[indexPath.row]
return cell
}
// method to run when table view cell is tapped
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
print("You tapped cell number \(indexPath.row).")
}
}
MyCustomCell.swift
I think the problem is probably in here since this is the main difference from the IB project.
import UIKit
class MyCustomCell: UITableViewCell {
var myCellLabel = UIMongolSingleLineLabel()
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.setup()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setup() {
self.myCellLabel.translatesAutoresizingMaskIntoConstraints = false
self.myCellLabel.centerText = false
self.myCellLabel.backgroundColor = UIColor.yellowColor()
self.addSubview(myCellLabel)
// Constraints
// pin top
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: self.contentView, attribute: NSLayoutAttribute.TopMargin, multiplier: 1.0, constant: 0).active = true
// pin bottom
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: self.contentView, attribute: NSLayoutAttribute.BottomMargin, multiplier: 1.0, constant: 0).active = true
// center horizontal
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self.contentView, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0).active = true
}
override internal class func requiresConstraintBasedLayout() -> Bool {
return true
}
}
Supplemental Code
I'll also include the code for the custom vertical label that I used in both projects above, but since the IB project works, I don't think the main problem is here.
import UIKit
#IBDesignable
class UIMongolSingleLineLabel: UIView {
private let textLayer = LabelTextLayer()
var useMirroredFont = false
// MARK: Primary input value
#IBInspectable var text: String = "A" {
didSet {
textLayer.displayString = text
updateTextLayerFrame()
}
}
#IBInspectable var fontSize: CGFloat = 17 {
didSet {
updateTextLayerFrame()
}
}
#IBInspectable var centerText: Bool = true {
didSet {
updateTextLayerFrame()
}
}
// MARK: - Initialization
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
setup()
}
func setup() {
// Text layer
textLayer.backgroundColor = UIColor.yellowColor().CGColor
textLayer.useMirroredFont = useMirroredFont
textLayer.contentsScale = UIScreen.mainScreen().scale
layer.addSublayer(textLayer)
}
override func intrinsicContentSize() -> CGSize {
return textLayer.frame.size
}
func updateTextLayerFrame() {
let myAttribute = [ NSFontAttributeName: UIFont.systemFontOfSize(fontSize) ]
let attrString = NSMutableAttributedString(string: textLayer.displayString, attributes: myAttribute )
let size = dimensionsForAttributedString(attrString)
// This is the frame for the soon-to-be rotated layer
var x: CGFloat = 0
var y: CGFloat = 0
if layer.bounds.width > size.height {
x = (layer.bounds.width - size.height) / 2
}
if centerText {
y = (layer.bounds.height - size.width) / 2
}
textLayer.frame = CGRect(x: x, y: y, width: size.height, height: size.width)
textLayer.string = attrString
invalidateIntrinsicContentSize()
}
func dimensionsForAttributedString(attrString: NSAttributedString) -> CGSize {
var ascent: CGFloat = 0
var descent: CGFloat = 0
var width: CGFloat = 0
let line: CTLineRef = CTLineCreateWithAttributedString(attrString)
width = CGFloat(CTLineGetTypographicBounds(line, &ascent, &descent, nil))
// make width an even integer for better graphics rendering
width = ceil(width)
if Int(width)%2 == 1 {
width += 1.0
}
return CGSize(width: width, height: ceil(ascent+descent))
}
}
// MARK: - Key Text Layer Class
class LabelTextLayer: CATextLayer {
// set this to false if not using a mirrored font
var useMirroredFont = true
var displayString = ""
override func drawInContext(ctx: CGContext) {
// A frame is passed in, in which the frame size is already rotated at the center but the content is not.
CGContextSaveGState(ctx)
if useMirroredFont {
CGContextRotateCTM(ctx, CGFloat(M_PI_2))
CGContextScaleCTM(ctx, 1.0, -1.0)
} else {
CGContextRotateCTM(ctx, CGFloat(M_PI_2))
CGContextTranslateCTM(ctx, 0, -self.bounds.width)
}
super.drawInContext(ctx)
CGContextRestoreGState(ctx)
}
}
Update
The entire code for the project is all here, so if anyone is interested enough to try it out, just make a new project and cut and paste the code above into the following three files:
ViewController.swift
MyCustomCell.swift
UIMongolSingleLineLabel.swift
The error is pretty trivial:
Instead of
self.addSubview(myCellLabel)
use
self.contentView.addSubview(myCellLabel)
Also, I would replace
// pin top
NSLayoutConstraint(...).active = true
// pin bottom
NSLayoutConstraint(...).active = true
// center horizontal
NSLayoutConstraint(...).active = true
with
let topConstraint = NSLayoutConstraint(...)
let bottomConstraint = NSLayoutConstraint(...)
let centerConstraint = NSLayoutConstraint(...)
self.contentView.addConstraints([topConstraint, bottomConstraint, centerConstraint])
which is more explicit (you have to specify the constraint owner) and thus safer.
The problem is that when calling active = true on a constraint, the layout system has to decide to which view it should add the constraints. In your case, because the first common ancestor of contentView and myCellLabel is your UITableViewCell, they were added to your UITableViewCell, so they were not actually constraining the contentView (constraints were between siblings not between superview-subview).
Your code actually triggered a console warning:
Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.
Which made me to look immediately at the way the constraints are created for your label.
I have tested your code and found the issue was in setting constraints please use below code part for setting constants in your "MyCustomCell.swift" file setup() function
let topConstraint = NSLayoutConstraint(item: myCellLabel, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 0)
let bottomConstraint = NSLayoutConstraint(item: myCellLabel, attribute: .Bottom, relatedBy: .Equal, toItem: self, attribute: .Bottom, multiplier: 1, constant: 0)
let centerConstraint = NSLayoutConstraint(item: myCellLabel, attribute: .CenterX, relatedBy: .Equal, toItem: self, attribute: .CenterX, multiplier: 1, constant: 0)
self.addConstraints([centerConstraint, topConstraint, bottomConstraint])
Also set clips to bound property to your cell lable in "viewcontroller.swift"
// create a cell for each table view row
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell:MyCustomCell = self.tableView.dequeueReusableCellWithIdentifier(cellReuseIdentifier) as! MyCustomCell
cell.myCellLabel.text = self.myStrings[indexPath.row]
cell.myCellLabel.clipsToBounds=true
return cell
}
For your ease I have uploaded my sample code on GitHub Dynamic Height Sample
Output is looking like this now
The problem seems to come from the vertical constraints in the cell
By putting them relative to self instead of self.contentView in MyCustomCell you can fix your problem
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.TopMargin, multiplier: 1.0, constant: 0).active = true
// pin bottom
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.BottomMargin, multiplier: 1.0, constant: 0).active = true
// center horizontal
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0).active = true
the full class would be:
import UIKit
class MyCustomCell: UITableViewCell {
var myCellLabel = UIMongolSingleLineLabel()
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.setup()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setup() {
self.myCellLabel.translatesAutoresizingMaskIntoConstraints = false
self.myCellLabel.centerText = false
self.myCellLabel.backgroundColor = UIColor.yellowColor()
self.addSubview(myCellLabel)
// Constraints
// pin top
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.TopMargin, multiplier: 1.0, constant: 0).active = true
// pin bottom
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.BottomMargin, multiplier: 1.0, constant: 0).active = true
// center horizontal
NSLayoutConstraint(item: myCellLabel, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0).active = true
}
override internal class func requiresConstraintBasedLayout() -> Bool {
return true
}
}
The thing you are missing is this function:
override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return heightValue
}
Im not so sure what you should do exactly, but by the fact that you know your labels you should be able to return an exact height value for each cell in this method
I think you are missing to set constraints for tableView with superview. And try to increase estimated row height also.
Historic question alert:
Note that 15 years later, you can now simply
yourConstraint.setValue(0.75, forKey: "multiplier")
original QA:
I created two views in one superview, and then added constraints between views:
_indicatorConstrainWidth = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeWidth multiplier:1.0f constant:0.0f];
[_indicatorConstrainWidth setPriority:UILayoutPriorityDefaultLow];
_indicatorConstrainHeight = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeHeight multiplier:1.0f constant:0.0f];
[_indicatorConstrainHeight setPriority:UILayoutPriorityDefaultLow];
[self addConstraint:_indicatorConstrainWidth];
[self addConstraint:_indicatorConstrainHeight];
Now I want to change multiplier property with animation, but I can't figure out how to change the multipler property. (I found _coefficient in private property in header file NSLayoutConstraint.h, but it private.)
How do I change multipler property?
My workaround is to remove the old constraint and add the new one with a different value for multipler.
Here is an NSLayoutConstraint extension in Swift that makes setting a new multiplier pretty easy:
In Swift 3.0+
import UIKit
extension NSLayoutConstraint {
/**
Change multiplier constraint
- parameter multiplier: CGFloat
- returns: NSLayoutConstraint
*/
func setMultiplier(multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
Demo usage:
#IBOutlet weak var myDemoConstraint:NSLayoutConstraint!
override func viewDidLoad() {
let newMultiplier:CGFloat = 0.80
myDemoConstraint = myDemoConstraint.setMultiplier(newMultiplier)
//If later in view lifecycle, you may need to call view.layoutIfNeeded()
}
If you have only have two sets of multipliers that need to be applied, from iOS8 onwards you can add both sets of constraints and decide which should be active at any time:
NSLayoutConstraint *standardConstraint, *zoomedConstraint;
// ...
// switch between constraints
standardConstraint.active = NO; // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.active = YES;
[self.view layoutIfNeeded]; // or using [UIView animate ...]
Swift 5.0 version
var standardConstraint: NSLayoutConstraint!
var zoomedConstraint: NSLayoutConstraint!
// ...
// switch between constraints
standardConstraint.isActive = false // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.isActive = true
self.view.layoutIfNeeded() // or using UIView.animate
The multiplier property is read only. You have to remove the old NSLayoutConstraint and replace it with a new one to modify it.
However, since you know you want to change the multiplier, you can just change the constant by multiplying it yourself when changes are needed which is often less code.
A helper function I use to change multiplier of an existing layout constraint. It creates and activates a new constraint and deactivates the old one.
struct MyConstraint {
static func changeMultiplier(_ constraint: NSLayoutConstraint, multiplier: CGFloat) -> NSLayoutConstraint {
let newConstraint = NSLayoutConstraint(
item: constraint.firstItem,
attribute: constraint.firstAttribute,
relatedBy: constraint.relation,
toItem: constraint.secondItem,
attribute: constraint.secondAttribute,
multiplier: multiplier,
constant: constraint.constant)
newConstraint.priority = constraint.priority
NSLayoutConstraint.deactivate([constraint])
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
Usage, changing multiplier to 1.2:
constraint = MyConstraint.changeMultiplier(constraint, multiplier: 1.2)
Objective-C Version for Andrew Schreiber answer
Create the category for NSLayoutConstraint Class and add the method in .h file like this
#import <UIKit/UIKit.h>
#interface NSLayoutConstraint (Multiplier)
-(instancetype)updateMultiplier:(CGFloat)multiplier;
#end
In the .m file
#import "NSLayoutConstraint+Multiplier.h"
#implementation NSLayoutConstraint (Multiplier)
-(instancetype)updateMultiplier:(CGFloat)multiplier {
[NSLayoutConstraint deactivateConstraints:[NSArray arrayWithObjects:self, nil]];
NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:self.firstItem attribute:self.firstAttribute relatedBy:self.relation toItem:self.secondItem attribute:self.secondAttribute multiplier:multiplier constant:self.constant];
[newConstraint setPriority:self.priority];
newConstraint.shouldBeArchived = self.shouldBeArchived;
newConstraint.identifier = self.identifier;
newConstraint.active = true;
[NSLayoutConstraint activateConstraints:[NSArray arrayWithObjects:newConstraint, nil]];
//NSLayoutConstraint.activateConstraints([newConstraint])
return newConstraint;
}
#end
Later in the ViewController create the outlet for the constraint you want to update.
#property (strong, nonatomic) IBOutlet NSLayoutConstraint *topConstraint;
and update the multiplier where ever you want like below..
self.topConstraint = [self.topConstraint updateMultiplier:0.9099];
You can change the "constant" property instead to achieve the same goal with a little math. Assume your default multiplier on the constraint is 1.0f. This is Xamarin C# code which can be easily translated to objective-c
private void SetMultiplier(nfloat multiplier)
{
FirstItemWidthConstraint.Constant = -secondItem.Frame.Width * (1.0f - multiplier);
}
As is in other answers explained: You need to remove constraint and create new one.
You can avoid returning new constraint by creating static method for NSLayoutConstraint with inout parameter, which allows you to reassign passed constraint
import UIKit
extension NSLayoutConstraint {
static func setMultiplier(_ multiplier: CGFloat, of constraint: inout NSLayoutConstraint) {
NSLayoutConstraint.deactivate([constraint])
let newConstraint = NSLayoutConstraint(item: constraint.firstItem, attribute: constraint.firstAttribute, relatedBy: constraint.relation, toItem: constraint.secondItem, attribute: constraint.secondAttribute, multiplier: multiplier, constant: constraint.constant)
newConstraint.priority = constraint.priority
newConstraint.shouldBeArchived = constraint.shouldBeArchived
newConstraint.identifier = constraint.identifier
NSLayoutConstraint.activate([newConstraint])
constraint = newConstraint
}
}
Example usage:
#IBOutlet weak var constraint: NSLayoutConstraint!
override func viewDidLoad() {
NSLayoutConstraint.setMultiplier(0.8, of: &constraint)
// view.layoutIfNeeded()
}
in Swift 5.x you can use:
extension NSLayoutConstraint {
func setMultiplier(multiplier: CGFloat) -> NSLayoutConstraint {
guard let firstItem = firstItem else {
return self
}
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(item: firstItem, attribute: firstAttribute, relatedBy: relation, toItem: secondItem, attribute: secondAttribute, multiplier: multiplier, constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
NONE OF THE ABOVE CODE WORKED FOR ME
SO AFTER TRYING TO MODIFY MY OWN CODE THIS CODE
This code is working in Xcode 10 and swift 4.2
import UIKit
extension NSLayoutConstraint {
/**
Change multiplier constraint
- parameter multiplier: CGFloat
- returns: NSLayoutConstraintfor
*/i
func setMultiplier(multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = self.shouldBeArchived
newConstraint.identifier = self.identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
}
#IBOutlet weak var myDemoConstraint:NSLayoutConstraint!
override func viewDidLoad() {
let newMultiplier:CGFloat = 0.80
myDemoConstraint = myDemoConstraint.setMultiplier(newMultiplier)
//If later in view lifecycle, you may need to call view.layoutIfNeeded()
}
Swift 5+
Based on Evgenii's answer, here is an elegant way to change the multiplier through extension.
extension NSLayoutConstraint {
func change(multiplier: CGFloat) {
let newConstraint = NSLayoutConstraint(item: firstItem,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = self.priority
NSLayoutConstraint.deactivate([self])
NSLayoutConstraint.activate([newConstraint])
}
}
And the usage:
myConstraint.change(multiplier: 0.6)
Simple answer, no extensions required. I tried for my case, worked fine for me.
So as multiplier is a get only property, we can simply set multiplier in the following way :
yourConstraintOutlet.setValue(yourDesiredMultiplierValue, forKey: "multiplier")
yourConstraintOutlet.setValue(0.75, forKey: "multiplier")
Yes w can change multiplier values just make an extension of NSLayoutConstraint
and use it like ->
func setMultiplier(_ multiplier:CGFloat) -> NSLayoutConstraint {
NSLayoutConstraint.deactivate([self])
let newConstraint = NSLayoutConstraint(
item: firstItem!,
attribute: firstAttribute,
relatedBy: relation,
toItem: secondItem,
attribute: secondAttribute,
multiplier: multiplier,
constant: constant)
newConstraint.priority = priority
newConstraint.shouldBeArchived = shouldBeArchived
newConstraint.identifier = identifier
NSLayoutConstraint.activate([newConstraint])
return newConstraint
}
self.mainImageViewHeightMultiplier = self.mainImageViewHeightMultiplier.setMultiplier(375.0/812.0)
Switch by changing the active constraint in code as suggested by many other answers did not work for me. So i created 2 constrains, one installed and the other not, bind both to the code, and then switch by removing one and adding the other.
For the sake of completeness, to bind the constrain drag the constrain to the code using mouse right button, just like any other graphic element:
I named one proportionIPad and the other proportionIPhone.
Then, add the following code, at viewDidLoad
override open func viewDidLoad() {
super.viewDidLoad()
if ... {
view.removeConstraint(proportionIphone)
view.addConstraint(proportionIpad)
}
}
I am using xCode 10 and swift 5.0
Here is an answer based on #Tianfu's answer in C#. Other answers that require activation and deactivation of constraints did not work for me.
var isMapZoomed = false
#IBAction func didTapMapZoom(_ sender: UIButton) {
let offset = -1.0*graphHeightConstraint.secondItem!.frame.height*(1.0 - graphHeightConstraint.multiplier)
graphHeightConstraint.constant = (isMapZoomed) ? offset : 0.0
isMapZoomed = !isMapZoomed
self.view.layoutIfNeeded()
}
#IBOutlet weak var viewHeightConstraint: NSLayoutConstraint!
let heightOfSuperview = self.view.bounds.height
viewHeightConstraint.constant = heightOfSuperview * 0.5
// this has the same effect as multiplier
I have a way. No need to re-create a constraint.
Assuming you have an imageView which you want to constraint its aspect ratio to match the image aspect ratio.
Create an aspect ratio constraint for the imageView and set multiplier to 1 and constant to 0.
Create an outlet for the aspect ratio constraint.
Change the constraint constant value at runtime, according the the image you load:
let multiplier = image.size.width / image.size.height
let (w, h) = (imageView.bounds.width, imageView.bounds.height)
let expectedW = h * multiplier
let diff = expectedW - h
imageViewAspectConstraint.constant = image.size.width >= image.size.height ? diff : -diff // multiplier is read-only, but constant is RW
note that you can simply yourConstraint.setValue(0.75, forKey: "multiplier")
or
Xcode 13.3.1, Swift 5.6 (swiftlang-5.6.0.323.62 clang-1316.0.20.8)
This is based on #Ullas Pujary's answer and I make it a little swifter and remove the warnings on firstItemandsecondItem`
extension NSLayoutConstraint {
public static func setMultiplier(_ newMultiplier: CGFloat, of constraint: inout NSLayoutConstraint) {
constraint.isActive = false
guard
let firstItem = constraint.firstItem,
let secondItem = constraint.secondItem
else {
return
}
let newConstraint = NSLayoutConstraint(item: firstItem,
attribute: constraint.firstAttribute,
relatedBy: constraint.relation,
toItem: secondItem,
attribute: constraint.secondAttribute,
multiplier: newMultiplier,
constant: constraint.constant)
newConstraint.priority = constraint.priority
newConstraint.shouldBeArchived = constraint.shouldBeArchived
newConstraint.identifier = constraint.identifier
newConstraint.isActive = true
constraint = newConstraint
}
}
One can read:
var multiplier: CGFloat
The multiplier applied to the second attribute participating in the constraint.
on this documentation page. Doesn't that mean that one should be able to modify multiplier (since it is a var)?