objective-c - CFReadStreamSetClient 回调函数 - 如何为 C 回调函数提供对包含类的引用？

Question

我在下面的网络读取流上使用客户端回调函数:

 -(void)connectToServer
{
    if([self isServerConfigured])
    {
        CFReadStreamRef readStream; 
        CFWriteStreamRef writeStream;
        CFHostRef host = CFHostCreateWithName(kCFAllocatorDefault, (CFStringRef)self.serverAddress);
        CFStreamCreatePairWithSocketToCFHost(kCFAllocatorDefault, host, self.port, &readStream, &writeStream);

        CFStreamClientContext myContext = {
            0,
            self,
            (void *(*)(void *info))CFRetain,
            (void (*)(void *info))CFRelease,
            (CFStringRef (*)(void *info))CFCopyDescription
        };

        CFOptionFlags registeredEvents = kCFStreamEventHasBytesAvailable |
        kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered;

        if(CFReadStreamSetClient(readStream, registeredEvents, serverCB, &myContext))
        {
            CFReadStreamScheduleWithRunLoop(readStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
        }
        if(!CFReadStreamOpen(readStream)){
            NSLog(@"Could not open read stream");
        }
    }
}

我希望这个回调函数能够调用当前对象(self)中的实例函数。 CFReadStreamSetClient 似乎不会允许我更改回调函数签名，因此我不能只将对当前对象的引用传递给我不认为的回调。

这是回调函数:

 void serverCB(CFReadStreamRef stream, CFStreamEventType event, void *myPtr)
{
    switch(event) {
        case kCFStreamEventHasBytesAvailable:
            [self readStreamData:stream];
            break;
        case kCFStreamEventErrorOccurred:
            NSLog(@"A Read Stream Error Has Occurred!");
            break;
        case kCFStreamEventEndEncountered:
            NSLog(@"A Read Stream Event End!");
            break;
        default:
            break;
    }
}

ServerCB 不知道在这个上下文中“self”是什么。有人可以指导我如何解决这个问题吗？

谢谢!

Answer 1

myPtr == self 在这种情况下，因为 self 是您为上下文的 info 字段提供的值.然后该字段通过最后一个参数传递给回调。所以:

void serverCB(CFReadStreamRef stream, CFStreamEventType event, void *myPtr) {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    {
        MyClass *self = [[(MyClass *)myPtr retain] autorelease];

        // ...
        // ...
        // ...

    }
    [pool drain];
}

(因为这是 Core Foundation 级别，所以不能保证自动释放池就位，所以在自动释放池中包装这些回调中的 Objective-C 很常见，以防万一。)