Detect backspace in UITextField

Question

Is there any way to detect when the backspace/delete key is pressed in the iPhone keyboard on a UITextField that is empty? I want to know when backspace is pressed only if the UITextField is empty.

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Based on the suggestion from @Alex Reynolds in a comment, I've added the following code while creating my text field:

[[NSNotificationCenter defaultCenter] addObserver:self
          selector:@selector(handleTextFieldChanged:)
              name:UITextFieldTextDidChangeNotification
            object:searchTextField];

This notification is received (handleTextFieldChanged function is called), but still not when I press the backspace key in an empty field. Any ideas?

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There seems to be some confusion around this question. I want to receive a notification when the backspace key is pressed. That's it. But the solution must also work when the UITextField is already empty.

Answer 1

Look into the UITextFieldTextDidBeginEditingNotification and UITextFieldTextDidEndEditingNotification notifications. If you begin and end editing, and the text doesn't change, what button was likely pressed?

Answer 2

This may be a long shot but it could work. Try setting the text field's text to a zero width space character \u200B. When backspace is pressed on a text field that appears empty, it will actually delete your space. Then you can just reinsert the space.

May not work if the user manages to move the caret to the left of the space.

Answer 3

Why. Someone could probably offer an alternative if you tell us what you want to do when Backspace is pressed on an empty text field.

Answer 4

Try the delegate

• (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

Then check if the range.length == 1... Which seems to be the case when backspace is hit...

Answer 5

Niklas Alvaeus's answer helped me out with a similar issue

I was limiting entry to a specific character set... but it was ignoring backspaces... so I had it check range.length == 1 before triming the string... it it was true i just return the string and don't trim it. See below

• (BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { NSCharacterSet *nonNumberSet = [[NSCharacterSet characterSetWithCharactersInString:@"0123456789."] invertedSet];

  if (range.length == 1){ return string; }else{ return ([string stringByTrimmingCharactersInSet:nonNumberSet].length > 0); }

}