ios - MPMediaPlayer indexOfNowPlayingItem 给出当前索引 9223372036854775807

Question

我正在尝试制作一个音乐播放器，这是我放置 NSLog 来显示当前索引的位置:

- (void) handle_NowPlayingItemChanged: (id) notification
{
    MPMediaItem *currentItem = [musicPlayer nowPlayingItem];
    NSUInteger currentIndex = [musicPlayer indexOfNowPlayingItem];
    UIImage *artworkImage = [UIImage imageNamed:@"NoSongImage.png"];
    MPMediaItemArtwork *artwork = [currentItem valueForProperty:MPMediaItemPropertyArtwork];

if (artwork) {
    artworkImage = [artwork imageWithSize: CGSizeMake (200, 200)];
}

[self.artwork setImage:artworkImage];

NSString *titleString = [currentItem valueForProperty:MPMediaItemPropertyTitle];
if (titleString) {
    self.songName.text = [NSString stringWithFormat:@"%@",titleString];
} else {
    self.songName.text = @"Unknown title";
}

    NSLog(@"%li", currentIndex);
}

这是我的 UITableView 的 didSelectRowAtIndexPath:

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
if (songsList == YES){
    NSUInteger selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    MPMediaItem *selectedItem = [[songs objectAtIndex:selectedIndex] representativeItem];
    [musicPlayer setQueueWithItemCollection:[MPMediaItemCollection collectionWithItems:[songsQuery items]]];
    [musicPlayer setNowPlayingItem:selectedItem];
    [musicPlayer play];
    songsList = NO;
}
else if (albumsList == YES && albumsSongsList == NO){
    albumsSongsList = YES;
    NSUInteger selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    MPMediaItem *selectedItem = [[albums objectAtIndex:selectedIndex] representativeItem];
    albumTitle = [selectedItem valueForProperty:MPMediaItemPropertyAlbumTitle];
    MPMediaItemArtwork *albumArtwork = [selectedItem valueForProperty:MPMediaItemPropertyArtwork];
    albumSelected = [albumArtwork imageWithSize: CGSizeMake (44, 44)];
    [self.tableView reloadData];
    [self.tableView setContentOffset:CGPointZero animated:NO];
}
else if (albumsSongsList == YES){
    albumsSongsList = NO;
    MPMediaQuery *albumQuery = [MPMediaQuery albumsQuery];
    MPMediaPropertyPredicate *albumPredicate = [MPMediaPropertyPredicate predicateWithValue: albumTitle forProperty: MPMediaItemPropertyAlbumTitle];
    [albumQuery addFilterPredicate:albumPredicate];
    NSArray *albumTracks = [albumQuery items];
    NSUInteger selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    MPMediaItem *selectedItem = [[albumTracks objectAtIndex:selectedIndex] representativeItem];
    [musicPlayer setQueueWithItemCollection:[MPMediaItemCollection collectionWithItems:[albumQuery items]]];
    [musicPlayer setNowPlayingItem:selectedItem];
    [musicPlayer play];
    }
}

BOOLS 确定 tableView willDisplayCell 要加载哪个表。以上都正确显示了 UITableView 和正确的内容。问题是，当我打开专辑并选择一首歌曲时，它似乎播放了专辑的第一首歌曲(在 tableView 的顶部)。如果我再次返回专辑并选择不同的歌曲，则会选择正确的歌曲。然后，如果我再次返回并选择一首歌曲，则会再次播放第一首歌曲并重复......

在我的 NSLog 中，播放第一首歌曲的原因是 currentIndex 为 9223372036854775807

为什么它返回NSNotFound？ selectedIndex(例如4)位于albumTracks数组中。对于歌曲来说，这种情况也发生了 1/3 次。非常感谢您的帮助。

Answer 1

NSNotFound 在 64 位系统上的值(value)是什么？什么是 2^63 - 1？