在主线程或后台线程中是否会调用NSNotificationCenter回调方法？

Question

我的代码只是播放下载的mp4文件并注册视图控制器以观察播放器结束的通知。

它不仅适用于iOS5，也适用于iOS4。

但我只是想知道NotificationCenter的回调方法是否会在后台线程或主线程中调用。 （loadMoviePlayerStateChanged：（NSNotification *）通知是在我的代码中的回调方法） 有谁知道到底如何？

- (void) playMovie:(NSURL *)fileURL { 
MPMoviePlayerViewController *MPVC = [[MPMoviePlayerViewController alloc] initWithContentURL:fileURL]; 

self.mMPVC = MPVC; 
self.mMPVC.moviePlayer.controlStyle = MPMovieControlStyleFullscreen; 

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(loadMoviePlayerStateChanged:) 
               name:MPMoviePlayerLoadStateDidChangeNotification 
              object:self.mMPVC.moviePlayer]; 

[MPVC.moviePlayer prepareToPlay]; 
[MPVC release]; 
} 

- (void) loadMoviePlayerStateChanged:(NSNotification*)notification { 
int loadState = self.mMPVC.moviePlayer.loadState; 
if(loadState & MPMovieLoadStateUnknown) { 
    IGLog(@"The load state is not known at this time."); 
    return; 
} 

[[NSNotificationCenter defaultCenter] removeObserver:self 
               name:MPMoviePlayerLoadStateDidChangeNotification 
               object:self.mMPVC.moviePlayer]; 

[self.mMPVC.view setFrame:self.view.bounds]; 

[[NSNotificationCenter defaultCenter] addObserver:self 
             selector:@selector(moviePlayBackDidFinish:) 
              name:MPMoviePlayerPlaybackDidFinishNotification 
              object:self.mMPVC.moviePlayer]; 

/* if I do not use performSelectorOnMainThread method to add subview to UIViewController`s view, 
the view of MPMoviePlayerViewController would not be removed from superview normally */ 

[self.view performSelectorOnMainThread:@selector(addSubview:) 
          withObject:self.mMPVC.view 
         waitUntilDone:YES]; 
[self.mMPVC.moviePlayer play]; 
} 

- (void) moviePlayBackDidFinish:(NSNotification*)notification { 
[self.mMPVC.moviePlayer stop]; 
[self.mMPVC.moviePlayer.view removeFromSuperview]; 

NSString* dstFilePath = [[_mPopupVC.mSelectedMovie decryptionFilePath] stringByAppendingPathExtension:@"mp4"]; 
[[NSFileManager defaultManager] removeItemAtPath:dstFilePath error:nil]; 

[[NSNotificationCenter defaultCenter] removeObserver:self 
               name:MPMoviePlayerPlaybackDidFinishNotification 
               object:self.mMPVC.moviePlayer]; 
} 

Answer 1

我得到的回答为我在苹果开发者网站的问题，答案是，

“通知安全线程自己和主线程上执行他们的选择。 然而，你的问题是你不应该像这样添加和删除播放器视图，请使用在视图控制器类中作为类别提供的presentModalVideo方法。“

我解决了我的问题。代码如下..

- (void) playMovie 
{ 
/* 
    *create and initialize MPMoviePlayerViewController with specified url and retain it 
    */ 
MPMoviePlayerViewController *MPVC = [[MPMoviePlayerViewController alloc] initWithContentURL:vodWebURL]; 
self.mMPVC = MPVC; 
[MPVC release]; 
self.mMPVC.moviePlayer.controlStyle = MPMovieControlStyleFullscreen; 
self.mMPVC.moviePlayer.shouldAutoplay = NO; 
[self.mMPVC.moviePlayer prepareToPlay]; 

    /* 
    *register movie player to NSNotificationCenter 
    */ 
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(loadMoviePlayerStateChanged:) 
               name:MPMoviePlayerLoadStateDidChangeNotification 
              object:self.mMPVC.moviePlayer];  
} 


- (void) loadMoviePlayerStateChanged:(NSNotification*)notification 
{ 
/* 
    *do your work for the state of the movie player 
    */ 
int loadState = self.mMPVC.moviePlayer.loadState; 
if(loadState & MPMovieLoadStateUnknown) { 
    NSLog(@"The load state is not known at this time."); 
    return; 
} else if(loadState & MPMovieLoadStatePlayable) { 
    NSLog(@"MPMovieLoadStatePlayable : The buffer has enough data that playback can begin, but it may run out of data before playback finishes."); 
} else if(loadState & MPMovieLoadStatePlaythroughOK) { 
    NSLog(@"MPMovieLoadStatePlaythroughOK : Enough data has been buffered for playback to continue uninterrupted."); 
} else if(loadState & MPMovieLoadStateStalled) { 
    NSLog(@"MPMovieLoadStateStalled : The buffering of data has stalled."); 
} 

/* 
    *set frame of the view of MPMoviePlayerViewController and add it 
    *call play method 
    */ 
[self.mMPVC.view setFrame:self.view.superview.bounds]; 
[self.view.superview addSubview:self.mMPVC.view]; 
[self.mMPVC.moviePlayer play]; 

[[NSNotificationCenter defaultCenter] removeObserver:self 
               name:MPMoviePlayerLoadStateDidChangeNotification 
               object:self.mMPVC.moviePlayer]; 

[[NSNotificationCenter defaultCenter] addObserver:self 
             selector:@selector(moviePlayBackDidFinish:) 
               name:MPMoviePlayerPlaybackDidFinishNotification 
              object:self.mMPVC.moviePlayer]; 
} 

- (void) moviePlayBackDidFinish:(NSNotification*)notification 
{ 
    /* 
    *remove the view of MPMoviePlayerViewController 
    *release MPMoviePlayerViewController 
    */ 
[self.mMPVC.moviePlayer stop]; 
[self.mMPVC.moviePlayer.view removeFromSuperview]; 
self.mMPVC = nil; 

[[NSNotificationCenter defaultCenter] removeObserver:self 
               name:MPMoviePlayerPlaybackDidFinishNotification 
               object:self.mMPVC.moviePlayer]; 
}