Getting size of UIView in init

Question

I have made a custom subclass of UIView in my iOS application, and I am trying to get the computed sizes of the view in the view's init method, so I can use them when creating subviews to put inside the custom view.

The custom view is inside a stack view, which assigns my view 1/3 of the total (main view) height.

My init looks like this:

var mySubView: UIImageView

required init?(coder aDecoder: NSCoder) {

    mySubView = UIImageView()
    super.init(coder: aDecoder)

    let viewWidth = Int(self.frame.size.width)
    let viewHeight = Int(self.frame.size.height)
    mySubView.frame = CGRect(x: 0, y: 0, width: viewWidth, height: viewHeight)
    mySubView.backgroundColor = UIColor.cyan

    self.addSubview(mySubView)
}

However, the heights and widths are not reported correctly. For instance, mySubView above only ends up filling about half of the total space of the custom view.

Any help would be greatly appreciated!

Answer 1

The initializer is called too early in the lifecycle of the view to accurately do layout unless you know the exact dimensions in advance. Even so, it is idiomatically the wrong place to do it.

Try using the layoutSubviews method as such:

class SubView: UIImageView {

    var mySubView: UIImageView

    required init?(coder aDecoder: NSCoder) {

        mySubView = UIImageView()
        mySubView.backgroundColor = UIColor.cyan

        super.init(coder: aDecoder)
        self.addSubview(mySubView)
    }

    override func layoutSubviews() {
        mySubView.frame = self.bounds
        super.layoutSubviews()
    }
}

Now the subview bounds will be set properly at the start of each layout pass. It’s a cheap operation.

Also, the bounds property of a UIView is the frame translated to the view’s internal coordinate space. This means that normally this is true: bounds = CGRect(x: 0, y: 0, width: frame.size.width, height: frame.size.height). I suggest reading the documentation on view layout.

Alternatively, you can ditch manual layout entirely and use AutoLayout to do this for you.

class SubView: UIImageView {

    var mySubView: UIImageView

    required init?(coder aDecoder: NSCoder) {

        mySubView = UIImageView()
        mySubView.backgroundColor = UIColor.cyan

        super.init(coder: aDecoder)
        self.addSubview(mySubView)

        mySubView.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
        mySubView.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
        mySubView.widthAnchor.constraint(equalTo: widthAnchor).isActive = true
        mySubView.heightAnchor.constraint(equalTo: heightAnchor).isActive = true
    }
}