ios - MPMediaQuery 无效值

Question

我正在运行 MPMediaQuery 以在用户的​​ iPod 库中查找歌曲，如下所示:

MPMediaQuery *songQuery = [MPMediaQuery songsQuery];

[songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:track.title forProperty:MPMediaItemPropertyTitle comparisonType:MPMediaPredicateComparisonEqualTo]];

[songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:track.album forProperty:MPMediaItemPropertyAlbumTitle comparisonType:MPMediaPredicateComparisonEqualTo]];

[songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:track.artist forProperty:MPMediaItemPropertyArtist comparisonType:MPMediaPredicateComparisonEqualTo]];


*** CRASH HERE ***
if (songQuery.items.count > 0) {

    return [songQuery.items objectAtIndex:0];

}

else {

    return nil;

}

应用程序崩溃并吐出:

'invalid value (nil) for property item_extra.title.'

我做错了什么吗？有没有更好的方法来查询歌曲？谢谢大家!

Answer 1

在这一行:

[songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:track.title forProperty:MPMediaItemPropertyTitle comparisonType:MPMediaPredicateComparisonEqualTo]];

track.title 的值为 nil。你需要做一个检查，比如:

if (track.title != nil)
{
[songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:track.title forProperty:MPMediaItemPropertyTitle comparisonType:MPMediaPredicateComparisonEqualTo]];
}

编辑:我建议对要添加为过滤谓词的每个变量进行检查，以确保它们也不为零!