将用户输入的UITextVIew内容限制为自己的框架

Question

Trying to create a large textbox of fixed size.

This problem is very similar to the 140 character constraint problem, but instead of stopping typing at 140 characters, I want to stop typing when the edge of the textView's frame is reached, instead of extending below into the abyss. Here is what I've got for the delegate method. Seems to always be off by a little bit. Any thoughts?

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
    BOOL edgeBump = NO;
    CGSize constraint = textView.frame.size;

    CGSize size = [[textView.text stringByAppendingString:text] sizeWithFont:textView.font 
                                                           constrainedToSize:constraint 
                                                               lineBreakMode:UILineBreakModeWordWrap];
    CGFloat height = size.height;

    if (height > textView.frame.size.height) {
        edgeBump = YES;
    }

    if([text isEqualToString:@"\b"]){
        return YES;
    } else if(edgeBump){
        NSLog(@"EDGEBUMP!");
        return NO;
    }   

    return YES;
}

EDIT: As per Max's suggestion below, here is the code that works (note, however, that autocorrect and cut do not work here):

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
    CGSize constraint = textView.frame.size;

    NSString *whatWasThereBefore = textView.text;

    textView.text = [textView.text stringByReplacingCharactersInRange:range withString:text];

    if (textView.contentSize.height >= constraint.height) {
        textView.text = whatWasThereBefore;
    }

    return NO;
}

Answer 1

I had similar problem and noticed that sizeWithFont returns the wrong size. I used yourTextView.contentSize instead. So you can add characters, obtain the content size and then delete newly added characters if content size is bigger then the maximum one.

Edit2: fixed

 - (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    UITextView* clone_tv = [[[UITextView alloc] initWithFrame: textView.frame] autorelease];
    clone_tv.text = [textView.text stringByReplacingCharactersInRange:range withString:text];

    return (clone_tv.contentSize.height <= textView.frame.size.height*2);
}

Notice the clone_tv. We are actually changing the text in clone text view, and not in the real one. In this case autocorrect and cut works. However I recommend you to create some ivar named cloneTextView in your view controller and use it every time. Doing like this you will avoid unnecessary allocations.