Animate UIView grow/shrink

Question

I have a UILabel I want to animate growing and shrinking. While the size changes I need the bottom left corner to remain static so that it always appears directly above a bottom toolbar. I am using the following code to make the label grow:

[UIView animateWithDuration:kAnimationDuration delay:0.0 options:UIViewAnimationCurveEaseInOut 
                 animations:^{  
    CGFloat lblHeight = 42.0f;
    [label setFrame:CGRectMake(0.0, 
                CGRectGetMaxY(self.view.bounds) - kBottomBarHeight - lblHeight, 
                CGRectGetMaxX(self.view.bounds), 
                lblHeight)];                
} completion:^(BOOL finished) { }];

and to make it shrink I use the same logic except that lblHeight is set to 17.0f

The view correctly grows but when I try to shrink it the frame change animation is not animated. It blips into the new size and then animates into the new origin/location. I need the frame change to be animated. Can anyone see what I'm doing wrong?

Mike Mike · Accepted Answer · 2012-06-01T12:50:04

After some tinkering I've managed to get the desired behavior by doing the following.

In the expand method, I use the UIView animation to alter the frame. In the shrink method, I use the UIView animation to alter the bounds and center.

I'm a little baffled as to why this works but trying to shrink with the frame does not. If anyone can share some insight into this that would be great.

Animate UIView grow/shrink

2 Answers