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I do use multiplier with center constraints in the storyboard, now I want to do the same programmatically but can't figure out how to.
No, this thread does not help since the accepted answer is a workaround that would not auto resize if the superview size happens to change later on.
The storyboard center X constraint:
What I've tried without success:
// Does not exist
buttonLeft.centerXAnchor.constraint(equalTo: centerXAnchor, multiplier: 0.5).isActivate = true
// error shown:
// Cannot convert value of type 'NSLayoutXAxisAnchor' to expected argument type 'NSLayoutConstraint.Attribute'
let newConstraint = NSLayoutConstraint(item: self, attribute: centerXAnchor, relatedBy: .equal, toItem: buttonLeft, attribute: centerXAnchor, multiplier: 0.5, constant: 0)
Is it possible?
Yes: how?
No: do you have any explaination of why wouldn't it be possible programmatically? Does this thing is a syntaxic sugar hidding something more complexe? I'm lost..
And yep, it works as expected when this constraint is set using the storyboard
So it's possible, I missused the centerXAnchor instead of using .centerX
Also the order in which I called each item was not correct:
// Not Working
NSLayoutConstraint(item: self, attribute: centerXAnchor, relatedBy: .equal, toItem: buttonLeft, attribute: centerXAnchor, multiplier: 0.5, constant: 0)
// Working
NSLayoutConstraint(item: buttonLeft, attribute: .centerX, relatedBy: .equal, toItem: self, attribute: .centerX, multiplier: 0.5, constant: 0)
Though I could not find any way to create the constraint using the anchors methods.
Try using self.view.translatesAutoresizingMaskIntoConstraints = false before adding the constraints programmatically.
In my Swift app, I need to update an AutoLayout constraint multiple times, so I have a function which does this. I'm having an issue with this constraint not being updated sometimes, and I've narrowed down the issue to being that it updates the first time the function is called, but not if that function is called again.
The code from the function looks like this:
let verticalSpace = NSLayoutConstraint(item: self.prompt, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1, constant: 10)
NSLayoutConstraint.activate([verticalSpace])
Does anyone know what could be causing this? Is there something which needs to be done in order to update a function multiple times?
You cannot have "competing" constraints. If you set the verticalSpace to 10, then set another verticalSpace to 20, which constraint should be used?
What you need to do is remove the existing constraint (or deactivate it), and then add/activate your new constraint.
Or...
Create your verticalConstraint and save a reference to it... then when you want to change it you can change the .constant however you wish.
Try this:
let verticalSpace = NSLayoutConstraint(item: self.prompt, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1, constant: 10)
NSLayoutConstraint.activate([verticalSpace])
view.layoutIfNeeded()
Edit:
I've just achieved this by the following rule.
Either
Step 1:
remove that constraint which you want to update.
Step 2:
Add constraint again.
or
Update constraint value.
In both cases you should have the reference of that constraint which you want to update.
How:
I have just added my demo code.I have programmatically added a view and and changed it's vertical constraint by button click.Just go through the code.
Upto viewDidLoad method:
import UIKit
class ViewController: UIViewController {
let someView = UIView()
var topValue:CGFloat = 10
var verticalConstraint:NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
//This below codes are used to add a red color UIView in center which has width and height both 100
someView.backgroundColor = UIColor.red
someView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(someView)
let horizontalConstraint = NSLayoutConstraint(item: someView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) //Center horizontally
verticalConstraint = NSLayoutConstraint(item: someView, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.top, multiplier: 1, constant: topValue) // center vertically.want to change that constraint later so took a variable.
let widthConstraint = NSLayoutConstraint(item: someView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) //width 100
let heightConstraint = NSLayoutConstraint(item: someView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) //height 100
view.addConstraints([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint])
}
And for each button click topConstant will be gradually updated.
This is the code for Either part which i mentioned.
self.view.removeConstraint(verticalConstraint)
verticalConstraint = NSLayoutConstraint(item: someView, attribute:
NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem:
view, attribute: NSLayoutAttribute.top, multiplier: 1, constant:
topValue)
self.view.addConstraint(verticalConstraint)
And this is the code for or part.
verticalConstraint.constant = topValue
And my buttonClick event method is basically like this.
#IBAction func updateView(_ sender: Any) {
topValue += 10
//In this case I've removed the previous constraint and add that constraint again with new Value
self.view.removeConstraint(verticalConstraint)
verticalConstraint = NSLayoutConstraint(item: someView, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.top, multiplier: 1, constant: topValue)
self.view.addConstraint(verticalConstraint)
//In this case I've just update that constraint value.Commented because we are using first method
//verticalConstraint.constant = topValue
}
And my output.
I see many solution and applied auto layout constrains but still i am not getting desired solution.
Current Result:
Constrains given to all button:
View Hierarchy:
Assuming that what do you want is letting the 3 buttons equal each others and filling the width of screen using the Interface Builder (with no code, i.e: not programmatically), this is a solution:
you don't need to add them in views. just follow these steps:
let's start with this:
note that the buttons don't have any constraints -yet-, just add them to the to the bottom of the view (or where ever you want to display them, for this solution, I will display them in bottom of the screen). Make sure that the 3 of them have the same size.
Adding constraints to the orange button:
add the following constraints:
leading, bottom space, and equal height.
Adding constraints to the blue button:
add the following constraints:
trailing, bottom space and equal height.
Adding constraints to the cyan button:
ctrl + drag from the cyan button to the orange button and add the following constraints: horizontal spacing and center vertically.
ctrl + drag from the cyan button to the blue button and add the following constraints: horizontal spacing.
bottom space and equal height.
So far so good, we are almost done!
Now, select the 3 buttons and add the following constraint: equal widths.
Your buttons should look like this:
Now, all you have to do is select each of the two horizontal spacing constraints and set their constants to 0 -from the size inspector-:
AND there you go:
I hope this helped, Cheers Up.
Sorry for solution in code.. .Swift 3.0:
let button1 = UIButton()
let button2 = UIButton()
let button3 = UIButton()
let buttons = [button1, button2, button3]
button1.backgroundColor = .red
button2.backgroundColor = .blue
button3.backgroundColor = .green
buttons.forEach {
$0.translatesAutoresizingMaskIntoConstraints = false
view.addSubview($0)
}
buttons.forEach {
let cnt1 = NSLayoutConstraint(item: $0, attribute: .centerY, relatedBy: .equal, toItem: view, attribute: .centerY, multiplier: 1, constant: 0)
let cnt2 = NSLayoutConstraint(item: $0, attribute: .height, relatedBy: .equal, toItem: view, attribute: .height, multiplier: 0.2, constant: 0)
view.addConstraints([cnt1, cnt2])
}
let cnt1 = NSLayoutConstraint(item: button1, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1, constant: 0)
let cnt2 = NSLayoutConstraint(item: view, attribute: .trailing, relatedBy: .equal, toItem: button3, attribute: .trailing, multiplier: 1, constant: 0)
let cnt3 = NSLayoutConstraint(item: button2, attribute: .width, relatedBy: .equal, toItem: button1, attribute: .width, multiplier: 1, constant: 0)
let cnt4 = NSLayoutConstraint(item: button3, attribute: .width, relatedBy: .equal, toItem: button2, attribute: .width, multiplier: 1, constant: 0)
let cnt5 = NSLayoutConstraint(item: button2, attribute: .leading, relatedBy: .equal, toItem: button1, attribute: .trailing, multiplier: 1, constant: 0)
let cnt6 = NSLayoutConstraint(item: button3, attribute: .leading, relatedBy: .equal, toItem: button2, attribute: .trailing, multiplier: 1, constant: 0)
view.addConstraints([cnt1, cnt2, cnt3, cnt4, cnt5, cnt6])
Are you trying to lay out three buttons horizontally that have equal height and width? I think you can achieve this without using UIViews. I set constraints like as follows.
This is a simulator screenshot.
I am initialising a view infoScreen and adding it as a subview of the screen with its bottom, left and right constraints set like this:
let left = NSLayoutConstraint(item: infoScreen, attribute: .Left, relatedBy: .Equal, toItem: view, attribute: .LeftMargin, multiplier: 1, constant: 0)
let right = NSLayoutConstraint(item: infoScreen, attribute: .Right, relatedBy: .Equal, toItem: view, attribute: .RightMargin, multiplier: 1, constant: 0)
var yConstraint: NSLayoutConstraint!
if (point.y < halfOfScreen) {
yConstraint = NSLayoutConstraint(item: infoScreen, attribute: .Top, relatedBy: .Equal, toItem: highlightedView, attribute: .CenterY, multiplier: 1, constant: radius + stalkLength)
}
else {
// This gets called the first time round.
yConstraint = NSLayoutConstraint(item: infoScreen, attribute: .Bottom, relatedBy: .Equal, toItem: highlightedView, attribute: .CenterY, multiplier: 1, constant: -radius - stalkLength)
}
view.addConstraints([left, right, yConstraint])
as well as it's height being set.
Then after a button within infoScreen is clicked, I'm calling infoScreen.removeFromSuperview().
Then the same function is used to reinitialise infoScreen with different parameters, and add it to the screen. However, this time it has its top constraint set instead of the bottom constraint.
In iOS 9 this works perfectly, however in iOS 8, it acts as if the bottom constraint is still set and messes up the view. If I run the code so that it never has the bottom constraint set (essentially skipping over the first run of the initialisation function), then it works fine in iOS 8. What could be causing this?
I'm new to AutoLayout and would like to display my UITextField at 100% width with a consistent 15px left and right margin, like so:
Typically I would do this using CGRect, setting the width to the containing view's width minus 30px, then offset the left side by 15px:
searchTextField.frame = CGRectMake(15, 0, view.frame.width - 30, 50)
But I'd like to learn AutoLayout for this sort of thing, since it's the way to go these days. I should note that I am doing everything programmatically -- no Storyboards here.
I'd love it if someone could help me out!
Update
Wow! Thank you for all the responses. I believe all of them would achieve what I'm trying to do, but there can only be one :)
Usually I use for this cocoapod that is dealing with constraints, but if you need pure apple solution documentation states:
You have three choices when it comes to programmatically creating
constraints: You can use layout anchors, you can use the
NSLayoutConstraint class, or you can use the Visual Format Language.
Approach with NSLayoutConstraints in your case would be:
NSLayoutConstraint(item: textField, attribute: .Leading, relatedBy: .Equal, toItem: parentView, attribute: .LeadingMargin, multiplier: 1.0, constant: 15.0).active = true
NSLayoutConstraint(item: textField, attribute: .Trailing, relatedBy: .Equal, toItem: parentView, attribute: .TrailingMargin, multiplier: 1.0, constant: -15.0).active = true
NSLayoutConstraint(item: textField, attribute: .Top, relatedBy: .Equal, toItem: parentView, attribute: .TopMargin, multiplier: 1.0, constant: 50.0).active = true
Remember that if you don't have any constraints in the view, they would be added automatically and you'll have to deal with them and conflicts that would be created by adding new constraints on runtime. To avoid this you could either create textField manually and add it to the view or set constraints with low priority in the Interface Builder .
Assuming the parent of the text field is view, do this after view.addSubview(searchTextField):
NSLayoutConstraint.activateConstraints([
searchTextField.leadingAnchor.constraintEqualToAnchor(view.leadingAnchor, constant: 15),
searchTextField.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor, constant: -15),
])
Use this code:
let topConstraint = NSLayoutConstraint(item: textField, attribute: NSLayoutAttribute.Top, relatedBy: .Equal, toItem: self.view, attribute: NSLayoutAttribute.Top, multiplier: 1.0, constant: 0)
let trailingConstraint = NSLayoutConstraint(item: textField, attribute: NSLayoutAttribute.Trailing, relatedBy: .Equal, toItem: self.view, attribute: NSLayoutAttribute.Trailing, multiplier: 1.0, constant: 15)
let leadingConstraint = NSLayoutConstraint(item: textField, attribute: NSLayoutAttribute.Leading, relatedBy: .Equal, toItem: self.view, attribute: NSLayoutAttribute.Leading, multiplier: 1.0, constant: 15)
let heightConstraint = NSLayoutConstraint(item: textField, attribute: NSLayoutAttribute.Height, relatedBy: .Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: 50)
self.view.addConstraint(topConstraint )
self.view.addConstraint(trailingConstraint)
self.view.addConstraint(leadingConstraint)
self.view.addConstraint(heightConstraint)
Set the constraints in storyboard.
Click on the text field then click on in the bottom left. From there you can choose constraints like that.
To use Auto Layout, you need to define constraints for your text field.Here, I have created four constraints(Leading, Trailing, Top and Height) related to its superview.
func addLabelConstraints(superView:UIView) {
let leading = NSLayoutConstraint(item: searchTextField, attribute: .Leading, relatedBy: .Equal, toItem: superView, attribute: .Leading, multiplier: 1, constant: 15)
superview!.addConstraint(leading)
let trailing = NSLayoutConstraint(item: searchTextField, attribute: .Trailing, relatedBy: .Equal, toItem: superView, attribute: .Trailing, multiplier: 1, constant: 15)
superView.addConstraint(trailing)
let top = NSLayoutConstraint(item: searchTextField, attribute: .Top, relatedBy: .Equal, toItem: superView, attribute: .Top, multiplier: 1, constant: 0)
superView.addConstraint(top)
let height = NSLayoutConstraint(item: searchTextField, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .Height, multiplier: 0, constant: 50)
superView.addConstraint(height)
}