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I'm running into a problem with the autolayout for my detail view in a UISplitViewController. My view hierarchy contains a UIImageView with a decorative element, and the image view's intrinsic size seems to be screwing up the layout of the rest of the controls.
These are the constraints I have specified for the image view:
H:[UIImageView:0xc83ba90]-(NSSpace(20))-|
H:|-(NSSpace(20))-[UIImageView:0xc83ba90]
UIImageView:0xc83ba90.bottom == UITextField:0xc83d2d0.bottom
V:[UIImageView:0xc83ba90 (3)]>,
H:[UIImageView:0xc83ba90 (532)] Hug:1 CompressionResistance:750
V:[UIImageView:0xc83ba90 (2)] Hug:250 CompressionResistance:750
The behavior I want is for the image view to be resized to fill its superview, as described by the top two constraints. The actual behavior I'm seeing is that the image view only takes up horizontal space described by its intrinsic size constraint. It also seems to be altering the layout of all of its sibling views, as though the superview were only laying out views in a rectangle as wide as the image view.
I thought that specifying the hugging priority of the image view as low as possible would let the other constraints override it to resize the image view. What am I doing wrong here?
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Here is the essential problem: the only way in which UIImageView interacts with Auto Layout is via its intrinsicContentSize property. That property provides the intrinsic size of the image itself, and nothing more.
In general, the intrinsic content size simplifies the layout, reducing the number of constraints you need. However, using the intrinsic content size often requires setting the view's content-hugging and compression-resistance (CHCR) priorities, which can add additional complications.
An ExampleOpen the Object Library on the right and add a label to the View Controller Scene. Select the label and center it horizontally and vertically in its superview using the Align menu at the bottom. With the label selected, open the Attributes Inspector and set the text of the label to Intrinsic Content Size.
Managing SubviewsStack views don't have an intrinsic content size, so you must set it either implicitly with Auto Layout constraints or explicitly via its intrinsicContentSize property.
So, I finally found a solution.
Solution is to increase the Hugging Priority of the superview to .defaultHigh and decrease the Compression Resistance Priority of the UIImageView to .defaultLow. This will let constraints override the image's Intrinsic Size.
Content Hugging Priority - The higher this priority is, the more a view resists growing larger than its intrinsic content size.
Content Compression Resistance Priority - The higher this priority is, the more a view resists shrinking smaller than its intrinsic content size.
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