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iOS: Limiting the character count on UITextField

August 5th, 2014

For some reason, I couldn’t find this anywhere else on the web, so here it is. To set a maximum character count on a UITextField, simply implement this UITextFieldDelegate method:

-(BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    int maxLength = 64;
    //you only need this check if you have more than one textfield on the view:
    if (textField == self.nameTextField) {
        if (textField.text.length - range.length + string.length > maxLength) {
            if (string.length > 1) { // only show popup if cut-and-pasting:
                NSString *message = [NSString stringWithFormat:@"That name is too long. Keep it under %d characters.", maxLength];
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Oops!"
                                                                message:message
                                                               delegate:nil
                                                      cancelButtonTitle:@"OK"
                                                      otherButtonTitles:nil];
                [alert show];
            }
            return NO;
        }
    }
    return YES;
}

Remember, this is a delegate method, so you have to specify that your UIViewController implements it:

@interface SomeViewController () <UITextFieldDelegate>

…and you have to set the delegate for the textfield:

self.nameTextField.delegate = self;

This can also be done for a UITextView with its delegate method:

-(BOOL) textView:(UITextField *)textView shouldChangeTextInRange:(NSRange)range replacementString:(NSString *)text {
    int maxLength = 64;
    //you only need this check if you have more than one textview on the view:
    if (textView == self.descriptionTextView) {
        if (textView.text.length - range.length + text.length > maxLength) {
            if (text.length > 1) { // only show popup if cut-and-pasting:
                NSString *message = [NSString stringWithFormat:@"That description is too long. Keep it under %d characters.", maxLength];
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Oops!"
                                                                message:message
                                                               delegate:nil
                                                      cancelButtonTitle:@"OK"
                                                      otherButtonTitles:nil];
                [alert show];
            }
            return NO;
        }
    }
    return YES;
}
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