ios - 如何在swift ios xcode中检测UIView大小何时更改？

Question

I am trying some stuffs out with CATiledLayer inside UIScrollView.

Somehow, the size of UIView inside the UIScrollView gets changed to a large number. I need to find out exactly what is causing this resize.

Is there a way to detect when the size of UIView(either frame, bounds) or the contentSize of UIScrollView is resized?

I tried

override var frame: CGRect {
    didSet {
        println("frame changed");
    }
}

inside UIView subclass,

but it is only called once when the app starts, although the size of UIView is resized afterwards.

Answer 1

There's an answer here:

https://stackoverflow.com/a/27590915/5160929

Just paste this outside of a method body:

override var bounds: CGRect {
    didSet {
        // Do stuff here
    }
}

Answer 2

viewWillLayoutSubviews() and viewDidLayoutSubviews() will be called whenever the bounds change. In the view controller.

Answer 3

You can also use KVO:

You can set a KVO like this, where view is the view you want to observe frame changes for:

self.addObserver(view, forKeyPath: "center", options: NSKeyValueObservingOptions.New, context: nil)

And you can get the changes with this notification:

override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: NSDictionary!, context: CMutableVoidPointer) {
    }

The observeValueForKeyPath will be called whenever the frame of the view you are observing changes.

Also remember to remove the observer when your view is about to be deallocated:

view.removeObserver(self, forKeyPath:"center")

Answer 4

You can create a custom class, and use a closure to get the updated rect comfortably. Especially handy when dealing with classes (like CAGradientLayer which want you to give them a CGRect ):

GView.swift :

import Foundation
import UIKit

class GView: UIView {

    var onFrameUpdated: ((_ bounds: CGRect) -> Void)?

    override func layoutSublayers(of layer: CALayer) {
      super.layoutSublayers(of: layer)
      self.onFrameUpdated?(self.bounds)
    }
}

Example Usage:

let headerView = GView()
let gradientLayer = CAGradientLayer()
headerView.layer.insertSublayer(gradientLayer, at: 0)
    
gradientLayer.colors = [
    UIColor.mainColorDark.cgColor,
    UIColor.mainColor.cgColor,
]
    
gradientLayer.locations = [
    0.0,
    1.0,
]
    
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.0)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 1.0)
    
headerView.onFrameUpdated = { _ in // here you have access to `bounds` and `frame` with proper values
    gradientLayer.frame = headerView.bounds
}

If you are not adding your views through code, you can set the Custom Class property in storyboard to GView .

Please note that the name GView was chosen as a company measure and probably choosing something like FrameObserverView would be better.

Answer 5

答案是正确的，尽管在我的情况下，我在情节提要中设置的约束导致 UIView 大小发生变化而没有回调任何检测功能。

Answer 6

STEP 1:viewWillLayoutSubviews

Called to notify the view controller that its view is about to layout its subviews

When a view's bounds change, the view adjusts the position of its subviews. Your view controller can override this method to make changes before the view lays out its subviews. The default implementation of this method does nothing.

STEP 2:viewDidLayoutSubviews

Called to notify the view controller that its view has just laid out its subviews.

When the bounds change for a view controller's view, the view adjusts the positions of its subviews and then the system calls this method. However, this method being called does not indicate that the individual layouts of the view's subviews have been adjusted. Each subview is responsible for adjusting its own layout.

Your view controller can override this method to make changes after the view lays out its subviews. The default implementation of this method does nothing.

Above these methods are called whenever bounds of UIView is changed

Answer 7

For UIViews, as easy as:

    override func layoutSubviews() {
        super.layoutSubviews()

        setupYourNewLayoutHereMate()
    }

Answer 8

You can use the FrameObserver Pod.

It is not using KVO or Method Swizzling so won't be breaking your code if the underlying implementation of UIKit ever changes.

whateverUIViewSubclass.addFrameObserver { frame, bounds in // get updates when the size of view changes
    print("frame", frame, "bounds", bounds)
}

You can call it on a UIView instance or any of its subclasses, like UILabel , UIButton , UIStackView , etc.