EXC_BAD_ACCESS 错误，内存管理问题

Question

我了解到此错误来自内存管理问题，例如向已释放的对象发送消息。在第二个“for”部分的第一行中，我在评论“输出有关 'info' 数组中歌曲的信息”之后立即收到错误消息。 info 数组是否没有存储我在第一个“for”部分中提供的对象？

还有其他想法吗？

MPMediaQuery *query = [[MPMediaQuery alloc] init]; //query iPod library
NSMutableArray *info; //create array to hold songs that fit
NSArray *allSongs = [query collections];

//only add those songs which have not
//been played since last login

for (MPMediaItem *recent in allSongs) {
    NSDate *lastPlayed = [recent valueForProperty:MPMediaItemPropertyLastPlayedDate];
    BOOL uploadInfo = [[PlayedSinceLastLogin alloc] initWithLastPlayedDateOfSong:lastPlayed] ;
    if (uploadInfo == YES) {
        [info addObject:recent];
    }
}

//output information about songs
//in the 'info' array

for (MPMediaItem *played in info) {
    NSString *playCount = [played valueForProperty:MPMediaItemPropertyPlayCount];
    NSString *lastPlayed = [played valueForProperty:MPMediaItemPropertyLastPlayedDate];
    NSString *songTitle =
    [played valueForProperty: MPMediaItemPropertyTitle];
    NSString *artistName =
    [played valueForProperty: MPMediaItemPropertyArtist];
    NSString *albumName =
    [played valueForProperty: MPMediaItemPropertyAlbumTitle];
    NSLog (@"\n %@ by %@, from album %@, played since last login.\nLast Played:%@.\nTotal Play Count: %@.", songTitle, artistName, albumName, lastPlayed,playCount);

}

Answer 1

看起来你实际上并没有为 info 创建一个 NSMutableArray 的实例来指向，所以错误的访问错误可能是由于试图将一些随机的内存位视为初始化对象.

改变

NSMutableArray *info;

到

NSMutableArray *info = [NSMutableArray array];