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POHow do I adjust the anchor point of a CALayer, when Auto Layout is being used?
 

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  1. POHow do I adjust the anchor point of a CALayer, when Auto Layout is being used?
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    <p><strong>Note</strong>: Things have moved on since this question was asked; see <a href="http://revealapp.com/blog/constraints-and-transforms.html" rel="noreferrer">here</a> for a good recent overview.</p> <hr> <p>Before auto layout, you could change the anchor point of a view's layer without moving the view by storing the frame, setting the anchor point, and restoring the frame. </p> <p>In an auto layout world, we don't set frames any more, but constraints don't seem up to the task of adjusting the position of a view back to where we want it to. You can hack the constraints to reposition your view, but on rotation or other resizing events, these become invalid again. </p> <p>The following bright idea doesn't work as it creates an "Invalid pairing of layout attributes (left and width)":</p> <pre><code>layerView.layer.anchorPoint = CGPointMake(1.0, 0.5); // Some other size-related constraints here which all work fine... [self.view addConstraint: [NSLayoutConstraint constraintWithItem:layerView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:layerView attribute:NSLayoutAttributeWidth multiplier:0.5 constant:20.0]]; </code></pre> <p>My intention here was to set the left edge of <code>layerView</code>, the view with the adjusted anchor point, to half of its width plus 20 (the distance I want inset from the left edge of the superview). </p> <p>Is it possible to change the anchor point, without changing the location of a view, in a view that is laid out with auto layout? Do I need to use hardcoded values and edit the constraint on every rotation? I do hope not. </p> <p>I need to change the anchor point so that when I apply a transform to the view, I get the correct visual effect. </p>
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    1. COGiven just what you have here it seems that you're going to end up with ambiguous layouts anyway even if you got the code above working. How does `layerView` know its width? Is it sticking its right side to something else?
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    2. COThat's covered in the `//Size-related constraints that work fine` - the layer view's width and height is derived from the superview's.
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