iOS textField限制字数，监听键盘删除按键

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

{

if ([str isEqualToString:@""]) // 判断删除操作

{

return YES; 

}

else if (textField.text.length == 12)  // 输入文字大于12位禁止输入

{

return  NO;

}

return YES;

}