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POHow do I get auto layout to reposition a view when it's sibling view changes size?
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  1. POHow do I get auto layout to reposition a view when it's sibling view changes size?
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    copied!<p>I have a view controller with two views (greenView, redView) and a switch:</p> <p><img src="https://i.stack.imgur.com/Tkhhb.png" alt="enter image description here"></p> <p>I have a constraint on the redView top space of 50px from greenView. Here are all the constraints on redView:</p> <p><img src="https://i.stack.imgur.com/KNxlS.png" alt="enter image description here"></p> <p>I have a switch that when tapped toggles the height of greenView from 50px to 100px.</p> <p>When I launch the app, the views are laid out as I want, but when the switch is tapped, the greenView frame changes from a height of 50 to 100, the redView doesn't do what I would expect - which is to shift it's y position 50px down to maintain the top space constraint it was assigned. I have an inequality constraint put on the bottom space of redView so there are no conflicts, and I am also calling <code>[self.redView layoutIfNeeded]</code>.</p> <p>Here's the relevant code:</p> <pre><code>- (IBAction)switchTapped { if (theSwitch.isOn) { greenView.frame = CGRectMake(0, 30, 320, 100); [redView layoutIfNeeded]; } else { greenView.frame = CGRectMake(0, 30, 320, 50); [redView layoutIfNeeded]; } </code></pre> <p>Why isn't redView's y position being updated?</p> <p>I have watched WWDC videos, but they seem to mention calling layoutIfNeeded in passing. What am I missing?</p> <p>Here's what it looks like when launched:</p> <p><img src="https://i.stack.imgur.com/Shmr6.png" alt="enter image description here"></p> <p>And here it is when the switch is tapped:</p> <p><img src="https://i.stack.imgur.com/FDgdW.png" alt="enter image description here"></p>
 

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