我有一个很好的小问题，当用户点击＆＃34;播放按钮时，＆＃34;调出标题，如果该标题的歌曲存在于iTunes中，则该歌曲开始播放。我现在被卡住了，因为当歌曲不存在时，我不确定如何显示提醒视图。
以下是查询：
- (void) queryMusic
{
MPMediaQuery *q = [[MPMediaQuery alloc] init];
[q addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:@"Beyoncé" forProperty:MPMediaItemPropertyArtist comparisonType:MPMediaPredicateComparisonEqualTo]];
[q addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:_DetailModal[0]
forProperty:MPMediaItemPropertyTitle comparisonType:MPMediaPredicateComparisonEqualTo]];
[q setGroupingType:MPMediaGroupingTitle];
self.player = [MPMusicPlayerController applicationMusicPlayer];
[self.player setRepeatMode:MPMusicRepeatModeAll];
[self.player setShuffleMode:MPMusicShuffleModeSongs];
[self.player setQueueWithQuery: q];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(handleStateChanged:)
name:MPMusicPlayerControllerPlaybackStateDidChangeNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver: self
selector: @selector (handle_PlaybackStateChanged:)
name: MPMusicPlayerControllerPlaybackStateDidChangeNotification
object: self.player];
[self.player beginGeneratingPlaybackNotifications];
}
使用handle_PlaybackStateChanged：
- (void) handle_PlaybackStateChanged: (id) notification {
MPMusicPlaybackState playbackState = [self.player playbackState];
if (playbackState == MPMusicPlaybackStatePaused) {
self.textLabel.text = @"play";
[PlayButton setTitle:@"STOP" forState:UIControlStateNormal]; // To set the title
NSLog (@"This is paused");
self.playBarButton.title = @"Play";
self.PlayButton = PlayButton;
[self.PlayButton setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
[playPauseButton setImage:[UIImage imageNamed:@"playbss.png"] forState:UIControlStateNormal];
} else if (playbackState == MPMusicPlaybackStatePlaying) {
self.textLabel.text = @"pause";
[PlayButton setTitle:@"Pause" forState:UIControlStateNormal];
self.PlayButton = PauseButton;
[playPauseButton setImage:[UIImage imageNamed:@"pausesss@2x.png"] forState:UIControlStateNormal];
NSLog (@"This is playing");
} else if (playbackState == MPMusicPlaybackStateStopped) {
self.textLabel.text = @"Play";
self.PlayButton = PlayButton;
[playPauseButton setImage:[UIImage imageNamed:@"playbss.png"] forState:UIControlStateNormal];
[self.player stop];
}
}
我刚试过这个：
MPMediaItem * nowPlayingItem = self.player.nowPlayingItem;
NSString *title = [nowPlayingItem valueForProperty:MPMediaItemPropertyTitle];
if (title == (id)[NSNull null] || title.length == 0) {
UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"Hello World!"
message:@"This is your first UIAlertview message."
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil];
[message show];
}
但不起作用。救命。