iphone - 进入前台时如何保存当前 MPMediaItem 的状态并响应更改的值

Question

所以我正在尝试开发一个使用 iPod 音乐库的音乐游戏。用户根据提示选择歌曲。因为我正在使用[MPMusicPlayerController iPodMusicPlayer]，所以用户可能在返回应用程序之前更改了 iPod 应用程序中的歌曲。如果是这种情况，我希望它调用[musicPlayer stop]. 不幸的是，当应用程序从后台返回时，我不知道如何保存当前播放的歌曲并与当前播放的歌曲进行对比。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"];

}

和

- (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"];

}

谁能帮我一把？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
   }