我在backgrounded NSURLSessionUploadTask 中获得了类似的结果，在 __ NSCFURLSessionUploadTask s > -URLSession：task：didCompleteWithError：委托回调。

I've had similar results with backgrounded NSURLSessionUploadTasks, which get deserialized as __NSCFURLSessionUploadTasks during the -URLSession:task:didCompleteWithError: delegate callback.

如果我是你，我会放弃这种方法，并使用构图（即在另一个对象中使 NSURLSession 成为一个ivar）。如果您需要使用 NSURLSession 存储一些信息，您可以将JSON编码的字典填充到 .sessionDescription 中。

If I were you, I'd give up on that approach, and use composition (i.e. make the NSURLSession an ivar in another object). If you need to store some info with the NSURLSession, you could stuff a JSON-encoded dictionary into the .sessionDescription.

以下是我过去为执行的代码：

#pragma mark - Storing an NSDictionary in NSURLSessionTask.description

// This lets us attach some arbitrary information to a NSURLSessionTask by JSON-encoding
// an NSDictionary, and storing it in the .description field.
//
// Attempts at creating subclasses or categories on NSURLSessionTask have not worked out,
// because the –URLSession:task:didCompleteWithError: callback passes an
// __NSCFURLSessionUploadTask as the task argument. This is the best solution I could
// come up with to store arbitray info with a task.

- (void)storeDictionary:(NSDictionary *)dict inDescriptionOfTask:(NSURLSessionTask *)task
{
    NSData *data = [NSJSONSerialization dataWithJSONObject:dict options:0 error:nil];
    NSString *stringRepresentation = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    [task setTaskDescription:stringRepresentation];
    [stringRepresentation release];
}

- (NSDictionary *)retrieveDictionaryFromDescriptionOfTask:(NSURLSessionTask *)task
{
    NSString *desc = [task taskDescription];
    if (![desc length]) {
        DDLogError(@"No description for %@", task);
        return nil;
    }
    NSData *data = [desc dataUsingEncoding:NSUTF8StringEncoding];
    NSDictionary *dict = (data ? (id)[NSJSONSerialization JSONObjectWithData:data options:0 error:nil] : nil);
    if (!dict) {
        DDLogError(@"Could not parse dictionary from task %@, description\n%@", task, desc);
    }
    return dict;
}