AVPlayerItem.loadedTimeRanges上的KVO是否可能？

Question

蘋果文檔暗示它，但你如何設置AVPlayerItem的loadedTimeRanges屬性的鍵值觀察？該屬性是一個NSArray不會改變，所以你不能只使用playerItem addObserver:self forKeyPath:@"loadedTimeRanges ...

或者是否有另一種方式來獲取通知或更新，只要此更改？

Answer 1

其實，我使用KVO for loadedTimeRanges沒有任何問題。也許你只是沒有設置正確的選擇？以下是對Apple的AVPlayerDemo中的一些代碼的非常微小的修改，對我來說它的工作非常好。

//somewhere near the top of the file 
NSString * const kLoadedTimeRangesKey = @"loadedTimeRanges"; 
static void *AudioControllerBufferingObservationContext = &AudioControllerBufferingObservationContext; 


- (void)someFunction 
{ 
    // ... 

    //somewhere after somePlayerItem has been initialized 
    [somePlayerItem addObserver:self 
         forKeyPath:kLoadedTimeRangesKey 
          options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew 
          context:AudioControllerBufferingObservationContext]; 

    // ... 
} 

- (void)observeValueForKeyPath:(NSString*) path 
        ofObject:(id)object 
        change:(NSDictionary*)change 
        context:(void*)context 
{ 
    if (context == AudioControllerBufferingObservationContext) 
    { 
     NSLog(@"Buffering status: %@", [object loadedTimeRanges]); 
    } 
} 

Answer 2

沒錯。 loadedTimeRanges不會改變，但其內部的對象會改變。你可以設置一個定時器來運行每一秒鐘（或者這樣）並檢查loadedTimeRanges中的值。然後你會看到你正在尋找的變化。

dispatch_queue_t queue = dispatch_queue_create("playerQueue", NULL); 

[player addPeriodicTimeObserverForInterval:CMTimeMake(1, 1) 
              queue:queue 
            usingBlock:^(CMTime time) { 
             for (NSValue *time in player.currentItem.loadedTimeRanges) { 
              CMTimeRange range; 
              [time getValue:&range]; 
              NSLog(@"loadedTimeRanges: %f, %f", CMTimeGetSeconds(range.start), CMTimeGetSeconds(range.duration)); 
             } 
            }];