objective-c – 如何使用AFNetworking立即强制取消NSOperation？

[[[HTTPRequestSingleton sharedClient] operationQueue] cancelAllOperations];

但这并不像我需要的那样“取消”操作.我读了NSOperationQueue docs并发现了这个：

Canceling an operation object leaves the object in the queue but notifies the object that it should abort its task as quickly as possible. For currently executing operations,this means that the operation object’s work code must check the cancellation state,stop what it is doing,and mark itself as finished. For operations that are queued but not yet executing,the queue must still call the operation object’s start method so that it can processes the cancellation event and mark itself as finished.

关于cancelAllOperations方法：

This method sends a cancel message to all operations currently in the queue. Queued operations are cancelled before they begin executing. If an operation is already executing,it is up to that operation to recognize the cancellation and stop what it is doing.

我的问题似乎特别涉及一个已经执行的操作,我想立即取消.使用AFNetworking,如何提醒操作它应该取消并丢弃有关请求的所有信息？

用于操作的代码

AFJSONRequestOperation *loginOperation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request,NSHTTPURLResponse *response,id JSON) {

    //operation was successful

    if (loginOperation.isCancelled)
    {
        //can't do this. variable 'loginOperation' is uninitialized when captured by block      
    }

} failure:^(NSURLRequest *request,NSError *error,id JSON) {

    //operation failed

}];