Question

我正在尝试在其播放列表中找出MPMusicPlayerController的nowPlayingItem的曲目编号。这将是超级简单的，除了相同的歌曲可以在同一播放列表中多次出现的事实（因为它们都指向同一个文件）。例如，如果播放列表由歌曲1，歌曲2，歌曲1，歌曲3，歌曲2组成，我就会坚持如何确定nowPlayingItem是否是播放列表中的第一个或第三个项目。 / p>

我最接近解决问题的方法是为MPMediaItem创建一个类别，它添加一个包含“播放列表中的数字”值的关联对象（NSNumber）和一个为每个MPMediaItem设置该值的MPMusicPlayerController的类别。将播放列表添加到队列之前的播放列表。

MPMediaItem + playlistNumber.h

#import <Foundation/Foundation.h>
#import <MediaPlayer/MediaPlayer.h>
#import <objc/runtime.h>
@interface MPMediaItem (playlistNumber)
-(NSNumber*)numberInPlaylist;
-(void)setNumberInPlaylist:(NSNumber *)number;
@end

MPMediaItem + playlistNumber.m

@implementation MPMediaItem (playlistNumber)
static NSString * numberInPlaylistKey;
-(NSNumber*)numberInPlaylist{
    return objc_getAssociatedObject(self, &numberInPlaylistKey);
}
-(void)setNumberInPlaylist:(NSNumber *)number{
    objc_setAssociatedObject(self, &numberInPlaylistKey, number, OBJC_ASSOCIATION_RETAIN);
}

@end

MPMusicPlayerController + NumberTracks.h

#import <Foundation/Foundation.h>
#import "MPMediaItem+PlaylistNumber.h"
#include <objc/runtime.h>
@interface MPMusicPlayerController (NumberTracks)

-(void)setQueueAndAddNumbersToItemCollection:(MPMediaItemCollection*)collection;
@end

MPMusicPlayerController + NumberTracks.m

#import "MPMusicPlayerController+NumberTracks.h"
@implementation MPMusicPlayerController (NumberTracks)
-(void)setQueueAndAddNumbersToItemCollection:(MPMediaItemCollection*)collection{
    /*
    NSEnumerator *enumerator = [[collection items] objectEnumerator];
    MPMediaItem * object;
    int numberInPlaylist = 1;
    while (object = [enumerator nextObject]) {
        NSNumber * number = [[NSNumber alloc] initWithInt:numberInPlaylist];
        [object setNumberInPlaylist:number];
        NSLog(@"%@", [object numberInPlaylist]);
        NSLog(@"%@", [[[collection items] objectAtIndex:numberInPlaylist-1] numberInPlaylist]);
        NSLog(@"%@", [[[collection items] objectAtIndex:numberInPlaylist-1] valueForProperty:MPMediaItemPropertyTitle]);
        numberInPlaylist++;
    }
    */
    /*
    for (int numberInPlaylist = 1; numberInPlaylist <= collection.count; numberInPlaylist++) {
        NSNumber * number = [[NSNumber alloc] initWithInt:numberInPlaylist];
        [[[collection items] objectAtIndex:numberInPlaylist-1] setNumberInPlaylist:number];
        NSLog(@"%@", [[[collection items] objectAtIndex:numberInPlaylist-1] numberInPlaylist]);
        NSLog(@"%@", [[[collection items] objectAtIndex:numberInPlaylist-1] valueForProperty:MPMediaItemPropertyTitle]);
        [number release];
    }
    */
    NSArray * items = [collection items];
    NSUInteger number = 1;
    for (MPMediaItem * item in items) {
        [item setNumberInPlaylist:[NSNumber numberWithInt: number++]];
        NSLog(@"%@", item.numberInPlaylist);

    }
    [self setQueueWithItemCollection:collection];
    [self play];
    [self pause];
    [self skipToBeginning];
    //The play/pause/skipToBeginnng is so that the nowPlayingItem is actually the first item in the queue
}
@end

在NumberTracks类别实现中，我尝试了3种不同的方式（两个大的注释部分和一个大的未注释部分）来实现numberInPlaylist“property”的赋值。但是，当我尝试获取nowPlayingItem MPMediaItem时，numberInPlaylist值始终返回（null）。它实际上可以实现我想要做的事情吗？在这一点上，我正逐渐失去信心。

Answer 1

MPMusicPlayerController中有一个名为indexOfNowPlayingItem的隐藏属性。不幸的是，我无法使用它，因为Apple将拒绝我的应用程序使用私有财产/方法。

nowPlayingItem在播放列表中的位置/向MPMediaItem添加类别

1 个答案: