ios - 在 NSDictionary 中插入 nil 时不会抛出异常

Question

所以我正在努力从用户的 Facebook 相册中提取照片，由于某种原因，NSDictionary 在插入 nil 时不会抛出异常。我已经在真实设备和 iOS 模拟器(均为 iOS 7)上对其进行了测试。也许调试器崩溃了，也许是 Facebook SDK 的错误。无论如何，我愿意听取您的意见。

更新:还有一件事我忘了提。在调试器中，在字典中插入 nil 对象后，调试器本身继续执行程序。而且我什至没有按下按钮“继续执行程序”。

这是片段

- (void)downloadAlbumsWithCompletionBlock:(void (^)(NSArray *albums, NSError *error))completionBlock;
{
    [FBRequestConnection startWithGraphPath:@"/me/albums"
                                 parameters:nil
                                 HTTPMethod:@"GET"
                          completionHandler:^(FBRequestConnection *connection, id result, NSError *error)
    {
        if (error)
        {
            NSLog(@"%@", error.localizedDescription);
            completionBlock(nil, error);
        }
        else
        {
            NSMutableArray *data = [result objectForKey:@"data"];
            NSMutableArray *albums = [NSMutableArray new];
            for (NSMutableDictionary *dict in data)
            {
                NSString *albumID = dict[@"id"];
                NSString *coverPhotoID = dict[@"cover_photo"];
                // coverPhotoID gets nil and then successfully gets put in NSDictionary
                // You can just write "NSString *coverPhotoID = nil;".
                NSString *description = dict[@"description"];
                NSString *name = dict[@"name"];
                NSDictionary *album = @{@"album_id": albumID,
                                      @"album_cover_photo_id": coverPhotoID,
                                      @"album_description": description,
                                      @"album_name": name };
                // Here an exception should be thrown but for some reason
                // we just quit out of the method. Result would be the same if we put
                // empty "return;" statement.
                // If we explicitly put nil, like 
                //   @"album_cover_photo_id": nil
                // we get compiler error.
                [albums addObject:album];
            }
            completionBlock(albums, nil);
        }
    }];
}

Answer 1

你写道:

// Here an exception should be thrown but for some reason
// we just quit out of the method. Result would be the same if we put empty "return;" statement.

很可能在某处捕获了异常。尝试在 Objective-C 异常抛出上设置断点(在 Xcode 中，转到“断点”选项卡，单击左下角的 + 并选择“添加异常断点”。确保参数设置为“Objective-C 异常”和“抛出时中断”)。