_rightBtn = [UIButton buttonWithType:UIButtonTypeCustom];

    _rightBtn.frame = CGRectMake(kWidth - -, , kWidth - _tf.frame.size.width-, );

    [_rightBtn setBackgroundImage:[UIImage imageNamed:@"send_un"] forState:UIControlStateNormal];

    [_rightBtn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];

    [_inputView addSubview:_rightBtn];

    //监听textfield的输入状态

    [[NSNotificationCenter defaultCenter] addObserver:self

                                             selector:@selector(textFieldDidChangeValue:)

                                                 name:UITextFieldTextDidChangeNotification

                                               object:_tf];

//这里可以通过发送object消息获取注册时指定的UITextField对象

- (void)textFieldDidChangeValue:(NSNotification *)notification

{

    UITextField *sender = (UITextField *)[notification object];

    if(sender.text.length != )

    {

        [_rightBtn setBackgroundImage:[UIImage imageNamed:@"send"] forState:UIControlStateNormal];

    }else

    {

        [_rightBtn setBackgroundImage:[UIImage imageNamed:@"send_un"] forState:UIControlStateNormal];

    }

}