主线程上的 NSOperation 和 NSNotificationCenter

Question

我有一个 NSOperation。完成后，我触发 NSNotificationCenter 让程序知道 NS 操作已完成并更新 gui。

据我了解， NSNotification 的侦听器不会在主线程上运行，因为 NSOperation 不在主线程上。

当我触发事件时，如何才能使侦听器在主线程上运行？

[[NSNotificationCenter defaultCenter] postNotificationName:@"myEventName" object:self]; 

Answer 1

更新：
调度队列使得在主线程上发布通知变得非常容易。

dispatch_async(dispatch_get_main_queue(),^{
   [[NSNotificationCenter defaultCenter] postNotification...];
});

要等待通知处理程序完成，只需将dispatch_async替换为dispatch_sync即可。

---

根据 notnoop 的回答，这里有一些基础设施，您可以使用它们在主线程上安全地发布通知，而无需等待它们完成。希望有人会觉得这有帮助！

NSNotificationCenter+Utils.h：

@interface NSNotificationCenter (Utils)

-(void)postNotificationOnMainThread:(NSNotification *)notification;
-(void)postNotificationNameOnMainThread:(NSString *)aName object:(id)anObject;
-(void)postNotificationNameOnMainThread:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo;

@end

NSNotificationCenter+Utils.m：

@interface NSNotificationCenter (Utils_Impl) {
}

-(void)postNotificationOnMainThreadImpl:(NSNotification*)notification;
-(void)postNotificationNameOnMainThreadImpl:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo;

@end

@implementation NSNotificationCenter (Utils)

-(void)postNotificationOnMainThread:(NSNotification *)notification {
    [notification retain];
    [notification.object retain];
    [self performSelectorOnMainThread:@selector(postNotificationOnMainThreadImpl:) 
                           withObject:notification
                        waitUntilDone:NO];
}

-(void)postNotificationNameOnMainThread:(NSString *)aName object:(id)anObject {
    [self postNotificationNameOnMainThread:aName object:anObject userInfo:nil];
}

-(void)postNotificationNameOnMainThread:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo {
    [aName retain];
    [anObject retain];
    [aUserInfo retain];

    SEL sel = @selector(postNotificationNameOnMainThreadImpl:object:userInfo:);
    NSMethodSignature* sig = [self methodSignatureForSelector:sel];
    NSInvocation* invocation = [NSInvocation invocationWithMethodSignature:sig];
    [invocation setTarget:self];
    [invocation setSelector:sel];
    [invocation setArgument:&aName atIndex:2];
    [invocation setArgument:&anObject atIndex:3];
    [invocation setArgument:&aUserInfo atIndex:4];
    [invocation invokeOnMainThreadWaitUntilDone:NO];
}

@end

@implementation NSNotificationCenter (Utils_Impl)

-(void)postNotificationOnMainThreadImpl:(NSNotification*)notification {
    [self postNotification:notification];
    [notification.object release];
    [notification release];
}

-(void)postNotificationNameOnMainThreadImpl:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo {
    [self postNotificationName:aName object:anObject userInfo:aUserInfo];
    [aName release];
    [anObject release];
    [aUserInfo release];
}

@end

NSInitation+Utils.h：

@interface NSInvocation (Utils)

-(void)invokeOnMainThreadWaitUntilDone:(BOOL)wait;

@end

NSInitation+Utils.m：

@implementation NSInvocation (Utils)

-(void)invokeOnMainThreadWaitUntilDone:(BOOL)wait
{
    [self performSelectorOnMainThread:@selector(invoke)
                           withObject:nil
                        waitUntilDone:wait];
}

@end

Answer 2

您可以使用 performSelectorOnMainThread:withObject:waitUntilDone: 使用辅助方法，其方式与以下示例类似。

.....
[self performSelectorOnMainThread:@selector(fireNotification) withObject:nil waitUntilDone:YES];
...

- (void)fireNotification {
  [[NSNotificationCenter defaultCenter] postNotificationName:@"myEventName" object:self]; 
}

如果您不等到完成，则需要考虑其他线程可能引用在调用主线程之前可能已经清理的对象的情况。

Answer 3

如果您使用的是 10.6，您还可以使用 setCompletionBlock：。
它的用法如下：

NSOperation*op= .... ;
[op setCompletionBlock:^{
    dispatch_async(dispatch_get_main_queue(),^{
        code to be run on the main thread after the operation is finished.
    });
}];

对于块和 GCD 的一般介绍，这篇文章非常有帮助。我找到了GCD & setCompletionBlock 比 NSNotification 更容易阅读。需要注意的是，它只能在 10.6 上运行！

Answer 4

为了扩展 Danra 的答案，这里是我整理的该类别的 ARC 兼容版本：

NSNotificationCenter+Threads.h

@interface NSNotificationCenter (Threads)

-(void)postNotificationOnMainThread:(NSNotification *)notification;
-(void)postNotificationNameOnMainThread:(NSString *)name object:(id)object;
-(void)postNotificationNameOnMainThread:(NSString *)name object:(id)object userInfo:(NSDictionary *)userInfo;

@end

NSNotificationCenter+Threads.m

@implementation NSNotificationCenter (Threads)

-(void)postNotificationOnMainThread:(NSNotification *)notification
{
    [self performSelectorOnMainThread:@selector(postNotification:) withObject:notification waitUntilDone:NO];
}

-(void)postNotificationNameOnMainThread:(NSString *)name object:(id)object
{
    [self postNotificationNameOnMainThread:name object:object userInfo:nil];
}

-(void)postNotificationNameOnMainThread:(NSString *)name object:(id)object userInfo:(NSDictionary *)userInfo
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [self postNotificationName:name object:object userInfo:userInfo];
    });
}

@end