iOS animating UILabel expand

Question

I have a UILabel that's initiated with 3 lines of text:

locationDescription = [[UILabel alloc]init];
locationDescription.numberOfLines = 3;
[locationDescription setTranslatesAutoresizingMaskIntoConstraints:NO];
[self addSubview:locationDescription];

I then have a button that expands the label:

- (void)buttonPressed:(UIButton *)sender{
    NSLog(@"Pressed");
    [UIView animateWithDuration:1
                     animations:^{locationDescription.numberOfLines = 0;}
     ];
}

The desired behavior for the label is to have each extra line reveal itself one at a time. The label expands fine, but the transition isn't animated and all the lines just show up at once.

What am I missing?

Answer 1

You can animate number of lines. It changes the intrinsicSize of the UILabel. You need to call layoutIfNeeded inside your animation block on the view containing the UILabel. Here I attach a tap gesture to the table to toggle it between having 0 (as many as you want) lines and 1 line.

 func tapLabel(tapGesture: UITapGestureRecognizer)
 {
    if let label = tapGesture.view as? UILabel {
      label.numberOfLines = label.numberOfLines == 0 ? 1 : 0
      UIView.animateWithDuration(0.5) {
        label.superview?.layoutIfNeeded()
      }
    }
 }