为什么 MPMusicPlayerController 调用其正在播放的项目更改选择器方法两次？

发布于 2024-11-29 01:38:51 字数 1059 浏览 1 评论 0原文

我正在为 iPhone 编写一个音乐播放列表编辑应用程序。
我正在订阅MPMusicPlayerController MPMusicPlayerControllerNowPlayingItemDidChangeNotification我是此通知的 @selector 方法出现问题当 nowPlayingItem: 更改时被多次调用。

我已将每个播放列表划分为各自的 MPMediaItemCollection 对象，当一个播放列表完成后，我通过在播放器上调用 -pause 来加载下一个播放列表，并传递一个新的 < code>MPMediaItemCollection 通过其 -setQueueWithItemCollection: 方法连接到音乐播放器控制器。然后，我将 nowPlayingItem 显式设置为我自己的一个项目，最后调用 -play。

        [musicPlayer pause];
        [musicPlayer setQueueWithItemCollection:[MPMediaItemCollection collectionWithItems:[selectedPrefs mediaItems]]];
        musicPlayer.nowPlayingItem = [selectedPrefs.playbackItems objectAtIndex:selectedPrefs.nowPlayingIndex];
        [musicPlayer play];

当我这样做时，@selector 会被调用两次以更改当前播放的项目。我怀疑这是因为 -setQueueWithItemCollection: 自动更改正在播放的项目以指向新集合中的第一个媒体项目，然后我在调用 -play 之前再次更改此项目代码>.

非常感谢。

原文

I am writing a music playlist editing application for the iPhone.
I am subscribing to the MPMusicPlayerController
MPMusicPlayerControllerNowPlayingItemDidChangeNotificationand I am
getting a problem where the @selector method for this notification
is being called more than once when the nowPlayingItem: changes.

I have divided up each playlist into their own MPMediaItemCollection objets, and when one playlist is finished I load the next one, by calling -pause on the player, passing a new MPMediaItemCollectionto the music player controller via its -setQueueWithItemCollection: method. I then explicitly set the nowPlayingItem to an item of item of my own and finally I call -play.

        [musicPlayer pause];
        [musicPlayer setQueueWithItemCollection:[MPMediaItemCollection collectionWithItems:[selectedPrefs mediaItems]]];
        musicPlayer.nowPlayingItem = [selectedPrefs.playbackItems objectAtIndex:selectedPrefs.nowPlayingIndex];
        [musicPlayer play];

When I do this the @selector is called twice for the now playing item changing. I suspect this is because -setQueueWithItemCollection:automatically changes the now playing item to point to the first media item in the new collection, and then I am changing this item again before calling -play.

Many thanks.

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