Introduction to the use of iOS NSNotification notifications

Let’s use the code to monitor keyboard pop-up/hide:

- (void)viewDidLoad {

    // 获取通知对象
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    
    /*
     注册监听，
     1>Observer参数：是哪个对象要监听
     2>selector参数：监听的对象收到通知后执行哪个方法
     3>name参数：监听通知的名称，明确监听哪个类型名称的通知，可以自定义通知名称。（如果不写，则会监听发出通知对象的所有通知）
     4>object参数：明确发出通知的对象.（如果不写，则会根据通知名称来监听）
     5>如果不写4.5参数，则会监听所有通知
     */
    [center addObserver:self selector:@selector(keyboardWillChange:) name:UIKeyboardWillChangeFrameNotification object:nil];
    
    /*
     发送通知
     1>Name参数：发送的通知名称
     2>object参数：发出通知的主体
     3>userinfo参数：发出通知的内容信息，为NSDictionary类型
     */
    [center postNotificationName:UIKeyboardDidChangeFrameNotification object:self userInfo:@{}];
    
}

// 收到通知后执行的方法
-(void)keyboardWillChange:(NSNotification *)notification{
    // 获取键盘改变通知中的userinfo CGRect
    CGRect rectEnd = [notification.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    // 从CGRect中获取Y将要移动到的位置
    CGFloat keyboardY = rectEnd.origin.y;
    // 根据键盘Y即将移动到的位置，计算出view的偏移量
    CGFloat tranformValue = keyboardY - ScreenHeight;
    // 设置view的transform
    self.view.transform = CGAffineTransformMakeTranslation(0, tranformValue);
}

Examples of commonly used notification codes for monitoring device status:

    // 设备改变旋转方向的通知
    UIDeviceOrientationDidChangeNotification;
    
    // 设备电池状态改变的通知
    UIDeviceBatteryStateDidChangeNotification;
    
    // 设备电池电量改变的通知
    UIDeviceBatteryLevelDidChangeNotification;
    
    // 近距离传感器通知（例如贴近耳朵）
    UIDeviceProximityStateDidChangeNotification;
    
    // 通知示例
    UIDevice *device = [UIDevice currentDevice];
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    [center addObserver:self selector:@selector(address) name:UIDeviceOrientationDidChangeNotification object:device];

What notifications and agents have in common:

Notifications and proxies can both complete communication between objects (the A object tells the B object what happened, and at the same time passes certain parameters to the B object)

The difference between notifications and agents:

Agents are a one-to-one relationship (one object can only notify one object of what happened)

Notifications can have a one-to-many relationship (one notification can be sent to multiple notification recipients)

Introduction to the use of iOS NSNotification notifications

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