设置IBOutlet的财产

Question

I created an outlet by draggin & dropping an UIImageView into the ViewController.swift file

@IBOutlet weak var imageView: UIImageView!

I want to set the property of imageView to

imageView.contentMode = .scaleToFill
imageView.clipsToBounds = true

Doing this

@IBOutlet weak var imageView: UIImageView! {
    self.imageView.contentMode = .scaleToFill
    self.imageView.clipsToBounds = true
}

XCode complains that

@IBOutlet attribute requires property to be mutable

How do I go on about this?

Answer 1

What you're trying to do is a perfectly acceptable way to set up an @IBOutlet 's properties… just don't reference other @IBOutlet s, or the main view, etc, as this may force the main view to load earlier than expected.

You just need to wrap your code inside a didSet block…

@IBOutlet weak var imageView: UIImageView! {    
    didSet {
        imageView.contentMode = .scaleToFill
        imageView.clipsToBounds = true
    }    
}

Answer 2

An outlet is basically just a link to that UI element in the storyboard.

So you link your UIImageView in the storyboard to an element in your UIViewController code and then you can access and change properties of that element once it is loaded.

The Problem

This is the wrong syntax for doing this:

@IBOutlet weak var imageView: UIImageView! {
    self.imageView.contentMode = .scaleToFill
    self.imageView.clipsToBounds = true
}

The reason for the following error

@IBOutlet attribute requires property to be mutable

is.. having a closure after a property declaration acts as a getter. As an example I can do this

let two = 2
let three = 3

var five: Int {
   return two + three
}

I cannot set any of the above values. two and three are let only (read only constants) and five is a computed property, so I can also only read that. I wont complicate the matter further but I would highly recommend giving this part of the documentation a read when you can.

Solution

You should have an outlet only:

@IBOutlet weak var imageView: UIImageView!

and then somewhere else in the code you can do things with it.

I think in your case it would be best on viewDidLoad. ViewDidLoad is called after the view and all of its outlets and properties have been set. So this is a safe place to start to use your outlets to further configure your view.

override func viewDidLoad() {
    super.viewDidLoad()

    self.imageView.contentMode = .scaleToFill
    self.imageView.clipsToBounds = true
}

Answer 3

First of all, it's not good approach to override outlet's getter. Secondly, technically you can override getter and setter of outlet.

In your case you defined getter, and forgot about setter. So you got get only variable.

    private var _someView: UIImageView!

    @IBOutlet weak var someView: UIImageView! {
    get {
        self.someView.contentMode = .scaleToFill
        self.someView.clipsToBounds = true
        return _someView
    }
    set {
        _someView = newValue
    }
}

You should use private variable to avoid recursion in getter.

Answer 4

Just try in this way and invoke this method inside viewDidLod()

func createRoundGreenImage(imageView : UIImageView, with image : 
String) {
self.imageView.contentMode = .scaleToFill
self.imageView.clipsToBounds = true
}