iOS Autolayout: Issue with UILabels in a resizing parent view

Question

I\'ve got a view that contains only a UILabel. This label contains multiline text. The parent has a variable width that can be resized with a pan gesture. My problem is t

Answer 1

I've fixed this issue after raising a bug with Apple. The issue that multiline text requires a two-pass approach to layout and it all relies on the property preferredMaxLayoutWidth

Here is the relevant code that needs to be added to a view controller that contains a multiline label:

- (void)viewWillLayoutSubviews
{
    // Clear the preferred max layout width in case the text of the label is a single line taking less width than what would be taken from the constraints of the left and right edges to the label's superview
    [self.label setPreferredMaxLayoutWidth:0.];
}

- (void)viewDidLayoutSubviews
{
    // Now that you know what the constraints gave you for the label's width, use that for the preferredMaxLayoutWidth—so you get the correct height for the layout
    [self.label setPreferredMaxLayoutWidth:[self.label bounds].size.width];

    // And then layout again with the label's correct height.
    [self.view layoutSubviews];
}

Answer 2

In Xcode 6.1 for iOS 7/8, I was able to get this to work by just setting preferredMaxLayoutWidth in a setter method that's called on my view to display the text for the label. I'm guessing it was set to 0 to begin with. Example below, where self.teachPieceLabel is the label. The label is wired up with constraints alongside other labels in a view in Interface Builder.

- (void)setTeachPieceText:(NSString *)teachPieceText {
      self.teachPieceLabel.text = teachPieceText;
      [self.teachPieceLabel setPreferredMaxLayoutWidth:[self.teachPieceLabel bounds].size.width];
}

Answer 3

Okay, I finally nailed it. The solution is to set the preferredMaxLayoutWidth in viewDidLayoutSubviews, but only after the first round of layout. You can arrange this simply by dispatching asynchronously back onto the main thread. So:

- (void)viewDidLayoutSubviews {
    dispatch_async(dispatch_get_main_queue(), ^{
        self.theLabel.preferredMaxLayoutWidth = self.theLabel.bounds.size.width;
    });
}

That way, you don't set preferredMaxLayoutWidth until after the label's width has been properly set by its superview-related constraints.

Working example project here:

https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/ch23p673selfSizingLabel4/p565p579selfSizingLabel/ViewController.m

EDIT: Another approach! Subclass UILabel and override layoutSubviews:

- (void) layoutSubviews {
    [super layoutSubviews];
    self.preferredMaxLayoutWidth = self.bounds.size.width;
}

The result is a self-sizing label - it automatically changes its height to accommodate its contents no matter how its width changes (assuming its width is changed by constraints / layout).