I am trying to build a custom UIView and am lost as far as initialization goes.
Code One
class CustomUIView: UIView {
var propertyToInitialize: CGRect
//Custom Initializer
override init(frame: CGRect) {
self.propertyToInitialize = CGRect(x: 0, y: 0, width: (superview?.frame.size.width)!, height: (superview?.frame.size.height)!)
super.init(frame: frame)
}
}
When I use the above code the error XCode gives me is as follows.
Error
Use of 'self' property access 'superview' before super.init initializes self
So I modified my code
Code Two
class CustomUIView: UIView {
var propertyToInitialize: CGRect
//Custom Initializer
override init(frame: CGRect) {
self.propertyToInitialize = CGRect()
super.init(frame: frame)
self.propertyToInitialize = CGRect(x: 0, y: 0, width: (superview?.frame.size.width)!, height: (superview?.frame.size.height)!)
}
}
Question
Is this bad design? Should I take a different approach? Am I initializing the property twice therefore, using more memory?
The whole thing is bad design. Make the propertyToInitialize an Optional wrapping a CGRect, so that it doesn't need a value at initialization time, and move your code to your view's didMoveToSuperview, which is the first moment where the concept of a superview has any meaning. Even better, don't make this a property at all; the superview can be examined at anytime you need this information, so it's pointless to duplicate it in a property.
I found the best approach for me was.
Code
class CustomUIView: UIView {
lazy var propertyToInitialize: CGRect = self.initializeProperty()
//Custom Initializer
override init(frame: CGRect) {
super.init(frame: frame)
}
func initializeProperty() -> CGRect {
let rect: CGRect = CGRect(x: 0, y: 0, width: (superview?.frame.size.width)!, height: (superview?.frame.size.height)!)
return rect
}
}
I think this is the best answer because I do not use the property until it is needed. And, can still get the superview size but not have to double initialize.
You need to call the super.init before you can access any properties in self, and put it into an entirely different function.
class CustomUIView: UIView {
var propertyToInitialize: CGRect?
init(frame: CGRect, property: CGRect) {
super.init(frame: frame)
self.propertyToInitialize = property
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
//Decode propertyToInitialize
}
}
Related
I have set up a subclassed UIView, and want to see the embedded image in IB - so I've set it as IBDesignable
#IBDesignable
class DieView: UIView {
#IBInspectable
var dieImage : UIImage = UIImage()
override init(frame: CGRect) {
super.init(frame: frame)
updateLayout()
}
convenience init() {
self.init(frame: CGRect.zero)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
updateLayout()
}
// for IB
override func prepareForInterfaceBuilder() {
super.prepareForInterfaceBuilder()
updateLayout()
}
func updateLayout() {
self.backgroundColor = .red
let profileImageView = UIImageView(frame: CGRect(x: 0, y: 0, width: self.frame.width, height: self.frame.height))
profileImageView.image = UIImage(named: "dice1")
profileImageView.contentMode = .scaleAspectFit
profileImageView.layer.masksToBounds = false
self.addSubview(profileImageView)
}
func showNumber(number: Int) {
}
}
The background colour changes, but the embedded image doesn't update. Why not?
From the documentation of the prepareForInterfaceBuilder():
Interface Builder waits until all objects in a graph have been created
and initialized before calling this method. So if your object’s
runtime configuration relies on subviews or parent views, those
objects should exist by the time this method is called.
which says that subviews should exist before this method is called. I'm not sure, but try to add image view before this is called. Also, you have to keep in mind that prepareForInterfaceBuilder() is called independently by interface builder. Read the docs for more info. Good Luck!
I know it may be the basic question but I am new to Swift.
Also, I have tried various solutions on SO but could not resolve the issue.
So if anyone can help me with my problem.
I have a custom UIVIEW class as follows:
class SearchTextFieldView: UIView, UITextFieldDelegate{
public var searchText = UITextField()
override init(frame: CGRect) {
super.init(frame: frame)
initializeUI()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
initializeUI()
}
func initializeUI() {
searchText.placeholder = "Enter model no"
searchText.backgroundColor = UIColor.white
searchText.textColor = UIColor.darkGray
searchText.layer.cornerRadius = 5.0
searchText.delegate=self
self.addSubview(searchText)
}
override func layoutSubviews() {
searchText.frame = CGRect(x: 20.0, y: 5.0, width: self.frame.size.width - 40,height : self.frame.size.height - 10)
}
}
Now I want to set text to SearchText textfield from another class which is as follows:
override func viewDidLoad() {
super.viewDidLoad()
setupUI()
// Do any additional setup after loading the view.
}
func setupUI() {
let searchTextFieldView = SearchTextFieldView()
self.view.addSubview(searchTextFieldView) //adding view containing search box view at the top
**searchTextFieldView.searchText.text = "My Text"**
}
I am using Storyboard. Also, I can see the textfield with placeholder text.only problem is I can not set text to it.
Can anybody help. Whats wrong in my code.
It is needed to call searchTextFieldView.setNeedsDisplay(), this will in turn call override func draw(_ rect: CGRect) in class SearchTextFieldView.
Add override func draw(_ rect: CGRect) {} in SearchTextFieldView, and try setting searchText.text = <someValue> in draw(). You can use a String property in SearchTextFieldView, to get <someValue> from the client (one who is using SearchTextFieldView) class.
You are creating you view via SearchTextFieldView(), while you have 2 available initializers init(frame:) and init?(coder:).
If you change
let searchTextFieldView = SearchTextFieldView()
with
let searchTextFieldView = SearchTextFieldView(frame: CGRect(x: 50, y: 50, width: 100, height: 100))
you will see the text.
You are not setting frame to the view. Also you are not loading the .xib in the view class. It should be like:-
class SearchTextFieldView: UIView, UITextFieldDelegate{
//MARK:- Initializer
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
initialize(withFrame: self.bounds)
}
override init(frame : CGRect) {
super.init(frame: frame)
initialize(withFrame: frame)
}
//MARK: - View Initializers
func initialize(withFrame frame : CGRect) {
Bundle.main.loadNibNamed("SearchTextFieldView", owner: self, options: nil)
view.frame = frame
view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
self.addSubview(view)
initializeUI()
}
}
Now you can call the below code in view controller:-
override func viewDidLoad() {
super.viewDidLoad()
setupUI()
// Do any additional setup after loading the view.
}
func setupUI() {
let searchTextFieldView = SearchTextFieldView(frame: ?*self.view.bounds)
self.view.addSubview(searchTextFieldView)
//adding view containing search box view at the top
searchTextFieldView.searchText.text = "My Text"
}
Don't forget to create an xib with name "SearchTextFieldView.xib" as you are loading that nib in your initialize function.
Hope it helps :)
add frame for the searchTextFieldView inside setupUI() method. because the View got loaded on the view but its doesn't have a frame (x,y position, width and height). Change your UIViewController's colour to grey and u can see the your view loaded on the left corner (0,0). set frame size for the view that will solve this problem.
I am writing a custom view that has two labels as subviews - titleLabel and subtitleLabel.
I added two #IBInspectable properties called titleText and subtitleText so that I can set the texts of the labels very easily in the storyboard.
class MyView : UIView {
var titleLabel: UILabel!
var subtitleLabel: UILabel!
#IBInspectable
var titleText: String? {
get { return titleLabel.text }
set {
titleLabel.text = newValue
let fontSize = // calculates appropriate font size for the text...
titleLabel.font = font.withSize(fontSize)
}
}
#IBInspectable
var subtitleText: String? {
get { return subtitleLabel.text }
set {
subtitleLabel.text = newValue
let fontSize = // calculates appropriate font size for the text...
subtitleLabel.font = font.withSize(fontSize)
}
}
override func draw(_ rect: CGRect) {
// here I make the view look prettier, irrelevant to the question
}
}
Now I need to initialise those two labels and add them as MyView's subviews. I thought I could do this in awakeFromNib:
override func awakeFromNib() {
titleLabel = UILabel(frame: CGRect(
x: ...,
y: ...,
width: ...,
height: ...))
self.addSubview(titleLabel)
subtitleLabel = UILabel(frame: CGRect(
x: ...,
y: ...,
width: ...,
height: ...))
self.addSubview(subtitleLabel)
}
So I added a MyView to the storyboard and set its properties with the properties inspector and I ran the app. It crashed.
Apparently, the IBInspectable properties are set before awakeFromNib so the labels have not been initialised by then.
This means that I need to initialise the labels in a method that is called before the IBInspectable properties are set.
What is a method that is called before IBInspectable properties are set that I can override to initialise the subviews?
This might be obvious but the correct method to put such things into is the initializer.
// called when initialized from code
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
// called when initialized from storyboard/xib
required init?(coder: NSCoder) {
super.init(coder: coder)
commonInit()
}
private func commonInit() {
// add subviews
}
Also, there is no real reason for optionals in your specific case:
let titleLabel: UILabel = UILabel()
You can add the labels as subviews and update frames later.
Say I want to init a UIView subclass with a String and an Int.
How would I do this in Swift if I'm just subclassing UIView? If I just make a custom init() function but the parameters are a String and an Int, it tells me that "super.init() isn't called before returning from initializer".
And if I call super.init() I'm told I must use a designated initializer. What should I be using there? The frame version? The coder version? Both? Why?
The init(frame:) version is the default initializer. You must call it only after initializing your instance variables. If this view is being reconstituted from a Nib then your custom initializer will not be called, and instead the init?(coder:) version will be called. Since Swift now requires an implementation of the required init?(coder:), I have updated the example below and changed the let variable declarations to var and optional. In this case, you would initialize them in awakeFromNib() or at some later time.
class TestView : UIView {
var s: String?
var i: Int?
init(s: String, i: Int) {
self.s = s
self.i = i
super.init(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
}
I create a common init for the designated and required. For convenience inits I delegate to init(frame:) with frame of zero.
Having zero frame is not a problem because typically the view is inside a ViewController's view; your custom view will get a good, safe chance to layout its subviews when its superview calls layoutSubviews() or updateConstraints(). These two functions are called by the system recursively throughout the view hierarchy. You can use either updateContstraints() or layoutSubviews(). updateContstraints() is called first, then layoutSubviews(). In updateConstraints() make sure to call super last. In layoutSubviews(), call super first.
Here's what I do:
#IBDesignable
class MyView: UIView {
convenience init(args: Whatever) {
self.init(frame: CGRect.zero)
//assign custom vars
}
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
override func prepareForInterfaceBuilder() {
super.prepareForInterfaceBuilder()
commonInit()
}
private func commonInit() {
//custom initialization
}
override func updateConstraints() {
//set subview constraints here
super.updateConstraints()
}
override func layoutSubviews() {
super.layoutSubviews()
//manually set subview frames here
}
}
Swift 5 Solution
You can try out this implementation for running Swift 5 on XCode 11
class CustomView: UIView {
var customParam: customType
var container = UIView()
required init(customParamArg: customType) {
self.customParam = customParamArg
super.init(frame: .zero)
// Setting up the view can be done here
setupView()
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setupView() {
// Can do the setup of the view, including adding subviews
setupConstraints()
}
func setupConstraints() {
// setup custom constraints as you wish
}
}
Here is how I do it on iOS 9 in Swift -
import UIKit
class CustomView : UIView {
init() {
super.init(frame: UIScreen.mainScreen().bounds);
//for debug validation
self.backgroundColor = UIColor.blueColor();
print("My Custom Init");
return;
}
required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented"); }
}
Here is a full project with example:
UIView Example Project (with SubView example)
Here is how I do a Subview on iOS in Swift -
class CustomSubview : UIView {
init() {
super.init(frame: UIScreen.mainScreen().bounds);
let windowHeight : CGFloat = 150;
let windowWidth : CGFloat = 360;
self.backgroundColor = UIColor.whiteColor();
self.frame = CGRectMake(0, 0, windowWidth, windowHeight);
self.center = CGPoint(x: UIScreen.mainScreen().bounds.width/2, y: 375);
//for debug validation
self.backgroundColor = UIColor.grayColor();
print("My Custom Init");
return;
}
required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented"); }
}
Assume a class that is derived from UIView as follows:
class MyView: UIView {
var myImageView: UIImageView
init(frame: CGRect) {
super.init(frame: frame)
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder)
}
...
If I wanted to have the same code in both of the initializers, like
self.myImageView = UIImageView(frame: CGRectZero)
self.myImageView.contentMode = UIViewContentMode.ScaleAspectFill
and NOT duplicate that code twice in the class implementation, how would I structure the init methods?
Tried approaches:
Created a method func commonInit() that is called after super.init -> Swift compiler gives an error about an uninitialized variable myImageView before calling super.init
Calling func commonInit() before super.init fails self-evidently with a compiler error "'self' used before super.init call"
What we need is a common place to put our initialization code before calling any superclass's initializers, so what I currently using, shown in a code below. (It also cover the case of interdependence among defaults and keep them constant.)
import UIKit
class MyView: UIView {
let value1: Int
let value2: Int
enum InitMethod {
case coder(NSCoder)
case frame(CGRect)
}
override convenience init(frame: CGRect) {
self.init(.frame(frame))!
}
required convenience init?(coder aDecoder: NSCoder) {
self.init(.coder(aDecoder))
}
private init?(_ initMethod: InitMethod) {
value1 = 1
value2 = value1 * 2 //interdependence among defaults
switch initMethod {
case let .coder(coder): super.init(coder: coder)
case let .frame(frame): super.init(frame: frame)
}
}
}
I just had the same problem.
As GoZoner said, marking your variables as optional will work. It's not a very elegant way because you then have to unwrap the value each time you want to access it.
I will file an enhancement request with Apple, maybe we could get something like a "beforeInit" method that is called before every init where we can assign the variables so we don't have to use optional vars.
Until then, I will just put all assignments into a commonInit method which is called from the dedicated initialisers. E.g.:
class GradientView: UIView {
var gradientLayer: CAGradientLayer? // marked as optional, so it does not have to be assigned before super.init
func commonInit() {
gradientLayer = CAGradientLayer()
gradientLayer!.frame = self.bounds
// more setup
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder)
commonInit()
}
init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
override func layoutSubviews() {
super.layoutSubviews()
gradientLayer!.frame = self.bounds // unwrap explicitly because the var is marked optional
}
}
Thanks to David I had a look at the book again and I found something which might be helpful for our deduplication efforts without having to use the optional variable hack. One can use a closure to initialize a variable.
Setting a Default Property Value with a Closure or Function
If a stored property’s default value requires some customization or setup, you can use a closure or global function to provide a customized default value for that property. Whenever a new instance of the type that the property belongs to is initialized, the closure or function is called, and its return value is assigned as the property’s default value. These kinds of closures or functions typically create a temporary value of the same type as the property, tailor that value to represent the desired initial state, and then return that temporary value to be used as the property’s default value.
Here’s a skeleton outline of how a closure can be used to provide a default property value:
class SomeClass {
let someProperty: SomeType = {
// create a default value for someProperty inside this closure
// someValue must be of the same type as SomeType
return someValue
}()
}
Note that the closure’s end curly brace is followed by an empty pair of parentheses. This tells Swift to execute the closure immediately. If you omit these parentheses, you are trying to assign the closure itself to the property, and not the return value of the closure.
NOTE
If you use a closure to initialize a property, remember that the rest of the instance has not yet been initialized at the point that the closure is executed. This means that you cannot access any other property values from within your closure, even if those properties have default values. You also cannot use the implicit self property, or call any of the instance’s methods.
Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/de/jEUH0.l
This is the way I will use from now on, because it does not circumvent the useful feature of not allowing nil on variables. For my example it'll look like this:
class GradientView: UIView {
var gradientLayer: CAGradientLayer = {
return CAGradientLayer()
}()
func commonInit() {
gradientLayer.frame = self.bounds
/* more setup */
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder)
commonInit()
}
init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
}
How about this?
public class MyView : UIView
{
var myImageView: UIImageView = UIImageView()
private func setup()
{
myImageView.contentMode = UIViewContentMode.ScaleAspectFill
}
override public init(frame: CGRect)
{
super.init(frame: frame)
setup()
}
required public init(coder aDecoder: NSCoder)
{
super.init(coder: aDecoder)
setup()
}
}
Does it necessarily have to come before? I think this is one of the things implicitly unwrapped optionals can be used for:
class MyView: UIView {
var myImageView: UIImageView!
init(frame: CGRect) {
super.init(frame: frame)
self.commonInit()
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder)
self.commonInit()
}
func commonInit() {
self.myImageView = UIImageView(frame: CGRectZero)
self.myImageView.contentMode = UIViewContentMode.ScaleAspectFill
}
...
}
Implicitly unwrapped optionals allow you skip variable assignment before you call super. However, you can still access them like normal variables:
var image: UIImageView = self.myImageView // no error
Yet another option using a static method (added 'otherView' to highlight scalability)
class MyView: UIView {
var myImageView: UIImageView
var otherView: UIView
override init(frame: CGRect) {
(myImageView,otherView) = MyView.commonInit()
super.init(frame: frame)
}
required init(coder aDecoder: NSCoder) {
(myImageView, otherView) = MyView.commonInit()
super.init(coder: aDecoder)!
}
private static func commonInit() -> (UIImageView, UIView) {
//do whatever initialization stuff is required here
let someImageView = UIImageView(frame: CGRectZero)
someImageView.contentMode = UIViewContentMode.ScaleAspectFill
let someView = UIView(frame: CGRect(x: 0, y: 0, width: 30, height: 30))
return (someImageView, someView)
}
}
Assign myImageView in both the init() methods based on a single image create function. As such:
self.myImageView = self.createMyImageView ();
For example, like such:
class Bar : Foo {
var x : Int?
func createX () -> Int { return 1 }
init () {
super.init ()
self.x = self.createX ()
}
}
Note the 'optional' use at Int?
Additionally, if the intention is to assign myImageView exactly once, it should be a let rather than a var. That rules out some solutions that only work for var.
Another complication is multiple instance variables with dependencies between them. This rules out inline initializers calling static methods.
These requirements can be addressed by overriding with convenience initializers, which delegate to a single designated initializer:
import UIKit
class MyView: UIView {
let myImageView: UIImageView
// Just to illustrate dependencies...
let myContainerView: UIView
override convenience init(frame: CGRect) {
self.init(frame: frame, coder: nil)!
}
required convenience init?(coder aDecoder: NSCoder) {
// Dummy value for `frame`
self.init(frame: CGRect(), coder: aDecoder)
}
#objc private init?(frame: CGRect, coder aDecoder: NSCoder?) {
// All `let`s must be assigned before
// calling `super.init`...
myImageView = UIImageView(frame: CGRect.zero)
myImageView.contentMode = .scaleAspectFill
// Just to illustrate dependencies...
myContainerView = UIView()
myContainerView.addSubview(myImageView)
if let aDecoderNonNil = aDecoder {
super.init(coder: aDecoderNonNil)
} else {
super.init(frame: frame)
}
// After calling `super.init`, can safely reference
// `self` for more common setup...
self.someMethod()
}
...
}
This is based on ylin0x81's answer, which I really like but doesn't work now (build with Xcode 10.2), as load from nib crashes with:
This coder requires that replaced objects be returned from initWithCoder:
This issue is covered on a separate question, with iuriimoz's answer suggesting to add #objc to the designated initializer. That entailed avoiding the Swift-only enum used by ylin0x81.