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I'm working on a cross-source solution for playing music (see project on Github). Every so called 'content source' has methods which fetch tracks, albums and artists by a search query (defined in SMKContentSource protocol). The methods work asynchronosly and require a completion handler passed which either accepts a result or a NSError.

At the moment I'm implementing a content source for Spotify. The following lines of code already work well, but in my opinion it is a bit risky solution:

    SPSession *strongSelf = weakSelf;
    dispatch_async([SMKSpotifyContentSource spotifyLocalQueue], ^{
        __block SPSearch *search = [[SPSearch alloc] initWithSearchQuery:predicate inSession:strongSelf];
        [search addObservationKeyPath:@"loaded" options:0 block:^(MAKVONotification *notification) {
            handler(search.albums, nil, nil);
            [search removeAllObservers];
            search = nil;
        }];
        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(SMKSpotifyDefaultLoadingTimeout * NSEC_PER_SEC));
        dispatch_after(popTime, [SMKSpotifyContentSource spotifyLocalQueue], ^{
            if (search) {
                handler(nil, nil, [NSError errorWithDomain:SMKSpotifyErrorDomain code:SMKSpotifyLoadingTimeoutErrorCode userInfo:nil]);
                [search removeAllObservers];
                search = nil;
            }
        });
    });

It's a pity but SPSearch doesn't provide any other way then to observe the loaded value. Now I'm asking about what others think about this implementation or tips for a better solution.

编辑：我也已经在 CocoaLibSpotify 上创建了一个问题，因为我认为 SPSearch 界面设计不佳：https ://github.com/spotify/cocoalibspotify/issues/148

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1 回答 1

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在将其发布给 CocoaLibSpotify 之后，他们告诉我，我已经在他们的文档中监督了一些帮助类，这些帮助类正是为这类问题而设计的。

正确的解决方案是使用SPAsyncLoading：

NSArray *someTracks = …; // Some tracks.

[SPAsyncLoading waitUntilLoaded:someTracks timeout:10.0 then:^(NSArray *loadedTracks, NSArray *notLoadedTracks) {
    NSLog(@"The following tracks are loaded: %@", loadedTracks);
}];
于 2013-03-30T13:48:34.943 回答