解决AssetsLibrary无法获取本地所有相册

    dispatch_async(dispatch_get_main_queue(), ^{
        [_assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
            if (group) {
                [self.groupArray addObject:group];
                [self performSelectorOnMainThread:@selector(reloadTableView) withObject:nil waitUntilDone:YES];
            }
        } failureBlock:^(NSError *error) {
            NSLog(@"Group not found!\n");
            self.title = @"访问照片失败"; // Photo-access is disabled.
        }];
    });