Setting the view's frame as old but its position changed

Question

I built a demo app to check the relationship between layer's anchorpoint, position and frame.

The initial look of the view looks like following:

In the code, I change that red view's anchor point, it will looks like this, which I could understand since change of anchor point will affect that view's frame.

to maintain the view's frame as original one, I used the following code:

We could see from the console's printout the frame has already remained the same.

However the view's final look looks like following, which still changes its position, how could this happen?

All the code looks like this:

Code are as following:

// Reserve original frame
let oldFrame = self.controlledView.frame

// Here I changed the anchorPoint which will cause that view's frame change
self.controlledView.layer.anchorPoint = CGPoint(x: 0, y: 0)

// to avoid the change of frame, set it back
self.controlledView.frame = oldFrame

// From the console's log the frame doesn't change, the red view's final 
// location should be the same with the first image. However it is aligned to the right, 
// which I could not understand.

Answer 1

From the CALayer Class Reference on Apple Documentation

You specify the value for this property using the unit coordinate space. The default value of this property is (0.5, 0.5), which represents the center of the layer’s bounds rectangle. All geometric manipulations to the view occur about the specified point. For example, applying a rotation transform to a layer with the default anchor point causes the layer to rotate around its center. Changing the anchor point to a different location would cause the layer to rotate around that new point.

From the UIView Class Reference on Apple Documentation

This rectangle defines the size and position of the view in its superview’s coordinate system. You use this rectangle during layout operations to size and position the view. Setting this property changes the point specified by the center property and the size in the bounds rectangle accordingly. The coordinates of the frame rectangle are always specified in points

So from my point of view, once the view is inside another view, when you change the frame you are changing it's center and size relative to his superview and not with itself.

To test my theory, i perform a small example

import UIKit

class ViewController: UIViewController {

    var insideView: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Setup Inside view
        self.insideView = UIView()

        var frame: CGRect = CGRectZero

        frame.size.height = 40.0
        frame.size.width = 40.0

        frame.origin.x = self.view.frame.size.width / 2 - 20.0
        frame.origin.y = self.view.frame.size.height / 2 - 20.0

        self.insideView.frame = frame
        self.insideView.backgroundColor = UIColor.redColor()

        self.view.addSubview(self.insideView)

        NSLog("One layer -> InsideView size: %@", NSStringFromCGRect(self.insideView.frame))
        // Output: 2015-05-22 20:13:11.342 test[42680:12030822] One layer -> InsideView size: {{140, 264}, {40, 40}}

        // Setup Another layer

        var insideLayer: CALayer = CALayer()

        insideLayer.backgroundColor = UIColor.blueColor().CGColor

        var insideLayerFrame: CGRect = self.insideView.layer.frame;
        insideLayerFrame.origin.x = 0.0
        insideLayerFrame.origin.y = 0.0

        insideLayer.frame = insideLayerFrame

        insideLayer.anchorPoint = CGPoint(x: 0.0, y: 0.0)

        self.insideView.layer.addSublayer(insideLayer)

        NSLog("Two layers -> InsideView size: %@", NSStringFromCGRect(self.insideView.frame))
        // Output: 2015-05-22 20:13:11.342 test[42680:12030822] Two layers -> InsideView size: {{140, 264}, {40, 40}}
    }
}

So i leave the layer of the view in it's position and add a new that i can manipulate.

And the result is:

Hope this can help :)