iOS UITextField限制输入字数

关于iOS的文本框有时需要限制字数，如手机号，在UITextField的代理单纯写一个判断，在字数超过限制时，这时再想删除就删除不掉，可以在代理这样写，就解决

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

{

    if (!string.length)

    {

        return YES;

    }

   

    if (textField.keyboardType == UIKeyboardTypeNumberPad)

    {

        if ([string rangeOfCharacterFromSet:[[NSCharacterSet decimalDigitCharacterSet] invertedSet]].location != NSNotFound)

        {

            return NO;

        }

    }

    

    NSString *updatedText = [textField.text stringByReplacingCharactersInRange:range withString:string];

    

    if (updatedText.length > 11) // 4 was chosen for SSN verification

    {

        if (string.length > 1)

        {

            // BasicAlert(@"", @"This field accepts a maximum of 4 characters.");

        }

        

        return NO;

    }    

    return YES;

}