Reloading keys in AVAsset when status is AVKeyValueStatusFailed

问题:

I'm doing the following:

• Create a new AVAsset with a given URL. That URL points to a video on a remote web server.
• Attempt to load the tracks property by calling loadValuesAsynchronouslyForKeys:completionHandler:
• The initial request fails, because no internet connection exists
• I notice that the request failed by calling statusOfValueForKey:error:
• I then wait for the connection to re-appear (using some reachability code). As soon as it does, I call loadValuesAsynchronouslyForKeys:completionHandler: again.

Here's where the problems begin. I would imagine that the AVAsset goes ahead and attempts to reload the tracks property since it failed previously. However, this does not seem to happen. statusOfValueForKey:error: will still return AVKeyValueStatusFailed, although a working internet connection is available and the video is playable.

Is there a way to reset the state for this given property and to attempt another load? Is there another way to work around this?

回答1:

1. Are you creating a new AVURLAsset or just reusing the previous one?
2. In the completion handler for loadValuesAsynchronouslyForKeys:completionHandler: are you dispatching back to the main thread?

What happens if you call this method again (or something similar) when you're ready to retry.

- (void)setContentURL:(NSURL *)contentURL {     if (_contentURL != contentURL) {         _contentURL = contentURL;          AVURLAsset *asset = [AVURLAsset URLAssetWithURL:_contentURL options:nil];          NSArray *requestedKeys = [NSArray arrayWithObjects:ISIVideoPlayerControllerTracksKey, ISIVideoPlayerControllerPlayableKey, nil];          [asset loadValuesAsynchronouslyForKeys:requestedKeys completionHandler: ^{              dispatch_async(dispatch_get_main_queue(), ^{                  [self prepareToPlayAsset:asset withKeys:requestedKeys];              });          }];     } }

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