监听一个控件内部的事件

控件监听

• 如果继承自UIControl

- (void)addTarget:(nullable id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents;

• 代理

• 通知

• 利用内部的某些机制

  • 比如重写UITextField的becomeFirstResponder和resignFirstResponder来监听UITextField的获得焦点和失去焦点事件

---

监听UITextField的获得焦点和失去焦点事件

• addTarget

[textField addTarget:target action:@selector(editingDidBegin) forControlEvents:UIControlEventEditingDidBegin];
[textField addTarget:target action:@selector(editingDidEnd) forControlEvents:UIControlEventEditingDidEnd];

UIControlEventEditingDidBegin
1.开始编辑
2.获得焦点
3.弹出键盘

UIControlEventEditingDidEnd
1.结束编辑
2.失去焦点
3.退下键盘

• delegate

textField.delegate = self;

#pragma mark - 
- (void)textFieldDidBeginEditing:(UITextField *)textField
{

}

- (void)textFieldDidEndEditing:(UITextField *)textField
{

}

• 通知

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(beginEditing) name:UITextFieldTextDidBeginEditingNotification object:textField];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(endEditing) name:UITextFieldTextDidEndEditingNotification object:textField];

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

- (void)beginEditing
{

}

- (void)endEditing
{

}

• 重写UITextField的becomeFirstResponder和resignFirstResponder方法

/**
 *  调用时刻 : 成为第一响应者(开始编辑\弹出键盘\获得焦点)
 */
- (BOOL)becomeFirstResponder
{

    return [super becomeFirstResponder];
}

/**
 *  调用时刻 : 不做第一响应者(结束编辑\退出键盘\失去焦点)
 */
- (BOOL)resignFirstResponder
{

    return [super resignFirstResponder];
}