How do I write a custom init for a UIView subclass in Swift

Question

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

User · Answer

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  quot init coder   has not been implemented quot                   func setupView                Can do the setup of the view  including adding subviews          setupConstraints                  func setupConstraints                setup custom constraints as you wish

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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

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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

User · Answer

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

User · Answer

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

[ios] How do I write a custom init for a UIView subclass in Swift?

Swift 5 Solution

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