Notification与多线程

分手后的思念是犯贱 2022-03-22 11:22 160阅读 0赞

一个`NSNotificationCenter`对象(通知中心)提供了在程序中广播消息的机制，它实质上就是一个通知分发表。这个分发表负责维护为各个通知注册的观察者，并在通知到达时，去查找相应的观察者，将通知转发给他们进行处理。

\[原文：An `NSNotificationCenter` object (or simply, **notification center**) provides a mechanism for broadcasting information within a program. An `NSNotificationCenter` object is essentially a notification dispatch table.\]

调试融云IM消息接收器回调方法时，碰到一些问题，下面将一一指出。

code:

// 消息接收器(聊天室功能中，A客户端发送消息，B客户端可在该方法中回调消息)
    - (void)onReceived:(RCMessage *)message
                  left:(int)nLeft
                object:(id)object {
          DLog(@"Thread = %@", [NSThread currentThread]);
    }

Log：

<BDChatRoomBaseController.m : -[BDChatRoomBaseController onReceived:left:object:] : 193> ——> Thread = <NSThread: 0x7fb7e2d6a340>{number = 4, name = (null)}

结论：当A客户端发送消息时，B客户端回调该方法是在子线程中异步回调的聊天结果。此时我想在此处发送消息接收的通知，作为他用！

代码：

- (void)onReceived:(RCMessage *)message left:(int)nLeft object:(id)object {
        DLog(@"Thread = %@", [NSThread currentThread]);
        [[NSNotificationCenter defaultCenter] postNotificationName:@"TESTMESSAGE_NOTIFICATION" object:nil];
    }

在控制器声明周期方法 viewDidLoad 中注册该通知。

code：

#pragma mark - View lifeCycle
    - (void)viewDidLoad {
        [super viewDidLoad];
        // 注册通知
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveMessage:) name:@"TESTMESSAGE_NOTIFICATION" object:nil];
    }
    
    // 通知响应方法
    - (void)receiveMessage:(NSNotification *)notification {
        DLog(@"Thread = %@", [NSThread currentThread]);
        DLog(@"userInfo = %@", notification.userInfo);
    }

Log：

<BDConversationController.m : -[BDConversationController receiveMessage:] : 27> ——> Thread = <NSThread: 0x7feb35859d60>{number = 9, name = (null)}
    <BDConversationController.m : -[BDConversationController receiveMessage:] : 28> ——> userInfo = (null)

结论：可以发现，子线程发出的通知，就会在子线程处理通知。

注意：在 \- (void)receiveMessage:(NSNotification \*)notification 刷新UI时，我们需要考虑到回到主线程刷新页面(线程通信)。

code:

// 通知响应方法
    - (void)receiveMessage:(NSNotification *)notification {
        DLog(@"Thread = %@", [NSThread currentThread]);
        DLog(@"userInfo = %@", notification.userInfo);
        dispatch_async(dispatch_get_main_queue(), ^{
            // 刷新UI
        });
    }

就可以成功的刷新UI了。

参考文档：

[NSNotificationCenter Class Reference][]

[NSNotificationCenter Class Reference]: https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/index.html#//apple_ref/doc/uid/TP40003701