UITextField

    // 设置文本框左边的内容 文本框内小间距
    UIView *leftView = [[UIView alloc] init];
    leftView.frame = CGRectMake(0, 0, 10, 0);
    self.messageField.leftView = leftView;
    self.messageField.leftViewMode = UITextFieldViewModeAlways

键盘处理：
    // 监听键盘通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

#pragma mark - 键盘处理
- (void)keyboardWillShow:(NSNotification *)note {
    // 取出键盘最终的frame
    CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    // 取出键盘弹出需要花费的时间
    double duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    // 修改约束
    self.bottomSpacing.constant = rect.size.height;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}

- (void)keyboardWillHide:(NSNotification *)note {
    // 取出键盘弹出需要花费的时间
    double duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    // 修改约束
    self.bottomSpacing.constant = 0;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}

第二种方式：
// 监听键盘通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillChangeFrame:) name:UIKeyboardWillChangeFrameNotification object:nil];
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

#pragma mark - 键盘处理
- (void)keyboardWillChangeFrame:(NSNotification *)note {
    // 取出键盘最终的frame
    CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    NSLog(@"%@",[NSValue valueWithCGRect:rect]);
    // 取出键盘弹出需要花费的时间
    double duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    
    // 修改约束
    self.bottomSpacing.constant = [UIScreen mainScreen].bounds.size.height - rect.origin.y;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}

 添加事件：

.....
[textfield addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
}
- (void)textFieldDidChange:(UITextField *)textField
{
    if ((textField.tag-100)%3==1) {
        if (textField.text.length > 2) {
            textField.text = [textField.text substringToIndex:2];
        }
    }
    if ([textField.text hasSuffix:@"."]) {
        textField.text = [textField.text substringToIndex:(textField.text.length-1)];
    }
    
}