UILabel text not automatically resized using Auto Layout

问题

I'm trying to implement a constrained UITableViewCell subclass and everything is working perfectly, except for the UILabel. The constraints that I've set up are definitely being enforced, but the text inside of the label does not resize to a smaller font size when the constraints clash. Instead, the height of the UILabel gets truncated and the font remains the same size, meaning the letters get cut off at the top and bottom.

Is there some method I have to call in order to get this to work? I would think Auto Layout would be smart enough to automatically resize the font size, so I'm kind of lost as to why this is happening.

Relevant Code:

self.label = [[UILabel alloc] initWithFrame:CGRectZero];
self.label.textColor = [UIColor whiteColor];
self.label.translatesAutoresizingMaskIntoConstraints = NO;
self.label.textAlignment = NSTextAlignmentCenter;
self.label.numberOfLines = 1;
[self.contentView addSubview:self.label];

NSLayoutConstraint *otherViewToLabelHorizontalConstraint =  // Make sure that the label is always to the right of the other view.
                    [NSLayoutConstraint constraintWithItem:self.label 
                                                 attribute:NSLayoutAttributeLeft 
                                                 relatedBy:NSLayoutRelationGreaterThanOrEqual
                                                    toItem:self.otherView 
                                                 attribute:NSLayoutAttributeRight 
                                                multiplier:1.0
                                                  constant:0.0];

NSLayoutConstraint *aTextFieldToLabelVerticalConstraint = 
                    [NSLayoutConstraint constraintWithItem:self.label 
                                                 attribute:NSLayoutAttributeTop 
                                                 relatedBy:NSLayoutRelationGreaterThanOrEqual
                                                    toItem:self.aTextField 
                                                 attribute:NSLayoutAttributeBottom 
                                                multiplier:1.0
                                                  constant:0.0];

Basically, these constraints are meant to enforce a cell where otherView is on the left, aTextField is on the right of otherView at the same y-level, and the label is below aTextField and to the right of the bottom of otherView.

As usual, thanks for any help with this.

回答1:

You need

myLabel.adjustsFontSizeToFitWidth = YES;
myLabel.minimumScaleFactor = .5f;

Then the label font size will be auto adjusted.

回答2:

Along with the setting of adjustsFontSizeToFitWidth and the minimumScaleFactor, you also need to set the content compression of the label to have a low priority. Check out the "Compression Resistance and Content Hugging" section of this objc.io essay. Basically, if your label has a lower compression resistance priority than the trailing constraint, the label should get resized:

[myLabel setContentCompressionResistancePriority:UILayoutPriorityDefaultLow
                                 forAxis:UILayoutConstraintAxisHorizontal];

回答3:

I solved this problem by setting a required width constraint to the view I was linking the label to.

   NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:self attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:width];

And make sure the priority for this constraint is set to UILayoutPriorityRequired.

[constraint setPriority:UILayoutPriorityRequired];

Text was resizing when pinning the label to the superview but not to the textfield, so I deduced there must be a problem with intrinsic sizes of elements involved in the layout calculation for the label's final width.

来源：https://stackoverflow.com/questions/17157778/uilabel-text-not-automatically-resized-using-auto-layout

标签

ios

uilabel

autolayout

nslayoutconstraint