iOS UITextField changes position when text is changed

Question

I use this to center a text field over something relevant:

[textField setCenter:[someObject center]];
[textField becomeFirstResponder];

This looks great, nice and centered over the object, ready to accept text. I'd like the text formated a certain way, so in the editing changed handler, I revise the text and set to the new text:

[textField setText:newText];

When I do this, the text field will jump to its the old position, from before it was centered. I'd like the text field to stay centered over the object.

My experience is that there is likely a better way to do this, i.e. move the text field and dynamically change its contents, without have to work around various quirks. Any advice?

Just a thought, but are you using auto layout? If so, try turning it off and see if the bug is still happening. — Amy Worrall, Dec 17 '12 at 16:39
Is there a way to turn off auto layout just for the control? — Yimin Rong, Dec 18 '12 at 16:05
Okay, I found a solution using replaceRange:withText: and UITextPosition and UITextRange classes, as well as setting it as a first responder, and there's probably a partridge in a pear tree somewhere in there, too. — Yimin Rong, Dec 19 '12 at 18:48

score 2 · Accepted Answer · answered Dec 17 '12 at 16:54

2

For Formatting the UITextField while editing you can try out the following code.

-(BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    if([string isEqualToString:@"4"]){
        UITextRange *range=textField.selectedTextRange;
        [textField replaceRange:range withText:@"Hi"];
        return NO;
    }
    return YES;
}

I have kept UITextfield with centre alignment. When it detects "4" at the start,centre or any where, it will replace it with "Hi",while maintaining it's centre align behaviour.

answered Dec 17 '12 at 16:54

NNikN

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Confirmed using setText: it still shifts the text field. It might work with replaceRange, but I need to change the text completely, not just replace the range. Looking into it more, it seems unbelievably difficult: no easy way to create UITextRange comprising the entire string, need to subclass two classes UITextRange and UITextPosition, the textField needs to be the first responder. Even after I do all this, I still don't know if the text field will shift. – Yimin Rong Dec 17 '12 at 22:30

score 0 · Answer 2 · answered Dec 18 '12 at 03:03

In addition to the code above, used the following to replace the existing text:

UITextPosition *p0 = [textField beginningOfDocument];
UITextPosition *p1 = [textField positionFromPosition:p0 offset:[[textField text] length]];
UITextRange *complete = [textField textRangeFromPosition:p0 toPosition:p1];
[textField replaceRange:complete withText:newText];

Ghastly solution for what should be an easy task!

iOS UITextField changes position when text is changed

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