Autolayout，根据子视图高度查看高度

Question

Using autolayout I'm developing a container UIView which contains a UILabel. I want to make the hight of the container view dynamically depending on the height of the UILabel.

I'm adding these constraints inside the container view, but I don't know how to tell the height of the UILabel because it's a multiline UILabel.

- (void) updateConstraints{

[self removeConstraints:self.constraints];

NSDictionary *views = NSDictionaryOfVariableBindings(_informationLabel);

// -- Constraints

[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-5-[_informationLabel]-5-|"
                                                             options:0
                                                             metrics:@{}
                                                               views:views]];

[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-5-[_informationLabel]-5-|"
                                                             options:0
                                                             metrics:@{}
                                                               views:views]];
[super updateConstraints];}

I've tried calculating the height with boundingRectWithSize and sending the height inside the metrics dictionary.

In the ViewController I haven't specify the height of the container view to let it resize depending on the height of subviews:

[constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[_informationView]"
                                                                         options:0
                                                                         metrics:@{}
                                                                           views:views]];

[constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[_informationView]-|"
                                                                         options:0
                                                                         metrics:@{}
                                                                           views:views]];

How I can make the container view height grow as uilabel height has to grow?

Answer 1

The intrinsicContentSize of multi-line text ( UILabel & NSTextView ) is ambiguous. This is because the height depends on the width which hasn't yet been calculated. To solve this, you have to allow a first pass of layout, and then set the newly added property preferredMaxLayoutWidth which solves this problem specifically.

// Inside superview
- (void)layoutSubviews
{
  [super layoutSubviews];
  self.informationLabel.preferredMaxLayoutWidth = self.informationLabel.frame.size.width;
  [super layoutSubviews];
}

Source: http://www.objc.io/issue-3/advanced-auto-layout-toolbox.html