#pragma mark -- TextField代理
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
/*
 // Method - one
    int limit = 3;
    return !([textField.text length] > limit && [string length] > range.length);
*/
 // Method - two
    if (textField == self.passWordLabel) {
        if (range.length + range.location > textField.text.length) {
            return NO;
        }
        NSUInteger newLength = [textField.text length] + [string length] - range.length;
        return newLength <= 4;
    }
    return YES;
}