如何保存当前 MPMediaItem 的状态并在进入前台时响应更改的值

Question

所以我正在尝试开发一款使用 iPod 音乐库的音乐游戏。用户根据提示选择歌曲。由于我使用的是 [MPMusicPlayerController iPodMusicPlayer]，因此用户可能在返回应用之前更改了 iPod 应用中的歌曲。如果是这种情况，我希望它调用 [musicPlayer stop]。不幸的是，我不知道如何保存当前播放的歌曲，并在应用程序从后台返回时将其与当前播放的歌曲进行检查。检查下面的代码。

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    MPMusicPlayerController *musicPlayer = [MPMusicPlayerController iPodMusicPlayer];
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    NSString *persistantID = [musicPlayer.nowPlayingItem valueForProperty:MPMediaItemPropertyPersistentID];
    [prefs setValue:persistantID forKey:@"NOWPLAYING_ID"];

}

？

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    MPMusicPlayerController *musicPlayer = [MPMusicPlayerController iPodMusicPlayer];
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    NSString *persistantID = [prefs stringForKey:@"NOWPLAYING_ID"];
    if (persistantID == [musicPlayer.nowPlayingItem valueForProperty:MPMediaItemPropertyPersistentID]) {
    }
    else {
        [musicPlayer stop];
    }
    [prefs setValue:nil forKey:@"NOWPLAYING_ID"];

}

谁能帮我一下吗 非常感谢。

Answer 1

- (void)applicationWillResignActive:(UIApplication *)application    {
    self.mediaItemSavedWhenAppSuspended = [musicPlayer nowPlayingItem];
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    MPMediaItem *nowPlayingItem = [musicPlayer nowPlayingItem];
    NSNumber *playingItem = [nowPlayingItem valueForProperty:MPMediaItemPropertyPersistentID];
    NSNumber *previousItem = [self.mediaItemSavedWhenAppSuspended valueForProperty:MPMediaItemPropertyPersistentID];

    if( [playingItem compare:previousItem] == NSOrderedSame )   {   //  same track still playing
   }