How to tell when a UILabel will be truncated an/or its line break position will change

Question

I have a multi-line UILabel (numberOfLines = 0). It\'s width can change at runtime, and sometimes this leads to truncation and/or re-wrapping. Some

Answer 1

You could know the size of label that is needed to display a particular NSString instance. For example, you could use that one:

- (CGSize)sizeWithFont:(UIFont *)font constrainedToSize:(CGSize)size lineBreakMode:(UILineBreakMode)lineBreakMode

Returns the size of the string if it were rendered with the specified constraints.

So what you want is to get CGSize for a particular string and check if it is not larger then UILabel size:

    UILabel *label;
    CGSize sizeNeeded = [label.text sizeWithFont:label.font constrainedToSize:CGSizeMake(label.bounds.size.width, MAXFLOAT)];
    if (sizeNeeded.height > label.bounds.size.height)
    {
        NSLog(@"String is truncated");
    }

More useful NSString methods you could find here: NSString UIKit Additions Reference

Ok, another way of doing what you want:

1) Create 2 UILabel with the same properties but second one (label2) will be with another one width.

2) Set alpha property of label2 to 0.0 in non-edit mode.

3) When edit mode begins make such animation:

// label1.alpha == 1.0, label2.alpha == 0.0 
{[UIView animateWithDuration:0.5 animations:^{
    label1.alpha = 0.0;
    label2.alpha = 1.0;
}];

4) When edit mode ends:

{[UIView animateWithDuration:0.5 animations:^{
    label1.alpha = 1.0;
    label2.alpha = 0.0;
}];

That will give you the same result as in Mail.app