如何检测 UITextField 何时变空

Question

I would like to perform a certain action when UITextField becomes empty (user deletes everything one sign after another or uses the clear option).

I thought about using two methods

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;

and

- (BOOL)textFieldShouldClear:(UITextField *)textField;

from

UITextFieldDelegate

I'm not sure how to detect the situation when the text field becomes empty? I tried with:

if ([textField.text length] == 0)

but it does't work as the fisrt of the above methods is called before the sign is deleted from the text field.

Any ideas?

Answer 1

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSRange textFieldRange = NSMakeRange(0, [textField.text length]);
    if (NSEqualRanges(range, textFieldRange) && [string length] == 0) {
        // Game on: when you return YES from this, your field will be empty
    }
    return YES;
}

It's useful to note that the field won't be empty until after this method returns, so you might want to set some intermediate state here, then use textFieldDidEndEditing: to know that the user is done emptying out the field.

Answer 2

If anyone who is searching Swift 4.2 version of this code is the following.

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let textFieldRange = NSRange(location: 0, length: textField.text?.count ?? 0)
    if NSEqualRanges(range, textFieldRange) && string.count == 0 {
        // Do whatever you want when text field is empty.
    }
    return true
}

Answer 3

The following code works as well.

-(void)textfieldDidChange:(UITextField *)textField

{

if (textField == first)
{

    [second becomeFirstResponder];

}
else if(textField == second)
{
    if (textField.text.length == 0)
    {
        [first becomeFirstResponder];
    }
    else
    {
        [third becomeFirstResponder];
    }

}
else if(textField == third)
{
    if (textField.text.length == 0)
    {
        [second becomeFirstResponder];
    }
    else
    {
         [four becomeFirstResponder];
    }

}

else if(textField == four)
{
    if (textField.text.length == 0)
    {
        [third becomeFirstResponder];
    }
    else
    {
        [four becomeFirstResponder];
    }

}
}

Added target for every textfield. For me I had to place cursor in previous field when text is empty the current textfield. Let me know if you need any clarity.

Answer 4

Here is a solution without using NSRange

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

    if(textField.text.length==1 && string.length==0){
        //textfield is empty
    }else{
        //textfield is not empty
    }

    return true;
}