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)
}
}
var. But the default best practice in Swift is to declare variables let unless there is a reason to declare them var. There was no such reason to do so in my code example above, hence let.
super.init() must be called before initializing self params?s and i Optional to keep things simple here. If they were not optional, they would also need to be initialized in the required initializer. Making them optional means they get to be nil when super.init() is called. If they weren't optional, they would indeed need to be assigned before calling super.init().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
}
}
commonInit method, but you can't place it after super in this case because you should initialise all properties BEFORE super call. Lol it seems like dead loop.
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:
return or the semicolons.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"); }
}
class TemperatureGraph: UIView {
var data: [Temperature]
required init(data: [Temperature]) {
self.data = data
super.init(frame: .zero)
}
required init?(coder aDecoder: NSCoder) {
self.data = []
super.init(coder: aDecoder)
}
}
another example
class TemperatureGraph: UIView {
var data: YourDataClass
required init(data: YourDataClass) {
self.data = data
super.init(frame: .zero)
}
required init?(coder aDecoder: NSCoder) {
self.data = YourDataClass()
super.init(coder: aDecoder)
}
}
another example
class TemperatureGraph: UIView {
var height: Int
var color: UIColor
required init(height: Int, color: UIColor) {
self.height = height
self.color = color
super.init(frame: .zero)
}
required init?(coder aDecoder: NSCoder) {
self.height = 180
self.color = .blue
super.init(coder: aDecoder)
}
}
The formula is
in required init, set the properties you added, then call super
in the coder init, set the properties you added to whatever defaults you prefer, then call super
That's it.
Note that you don't have to pass in the values, as long as you initialize them (in the two calls) before calling super.
For example
class Countdown: UIView {
var seconds: Int
required init() {
self.seconds = 10
super.init(frame: .zero)
}
required init?(coder aDecoder: NSCoder) {
self.seconds = 10
super.init(coder: aDecoder)
}
}
