Collect result of an asynchronous operation in UI thread

Question

Hi,

I need to get the results of an asynchronous operation and I am calling this in UI thread. Calling task.get() in UI thread throws invalid_operation exception. My code looks like:

IAsncOperation<int> sendHttpRequestsAsync()

{

return create_async([]() ->task<int>

{

return create_task([]()

{

return ;

}

)

}

);

}

I am calling this function from UI thread as below

int func1()

{

int status = -1;

auto sendOp = SendHttpRequestsAsync();

// Here i need to set value of status based on my operation's results but this method returns before sendOp completes. If i create a task for it and do a get() operation thereafter, that throws an exception.

return status;

}

Please indicate the correct way of doing this.

---

Parul Gupta

Answer 1

You can do a sendOp.then() and then retrieve the contents of the completion in the then completion handler. For example, take a look at this link: http://msdn.microsoft.com/en-us/library/windows/apps/Hh780559.aspx

If you are specifically looking for a sample that uses XmlHttpRequest2, you can get it off here: http://code.msdn.microsoft.com/HttpClient-sample-0c4d3c6c

The HttpRequest.cpp file has the DownloadAsync function that shows how you can retrieve the results of the async request.

Thanks,

Prashant.

---

@prashantphadke || Windows Store Developer Solutions #WSDevSol || Want more solutions? See our blog, Windows Store & Phone Developer Solutions

Answer 2

Any time consuming operation should be execute into a different worker thread. Inside the delegate of worker thread you may call Dispatcher->RunAsync() in order to notify the UI thread.

auto taskDelegate = [=](Windows::Foundation::IAsyncAction^ workItem)
	{
	
	// code block for executing in worker thread

			Dispatcher->RunAsync(CoreDispatcherPriority::High,
				ref new DispatchedHandler(
				[=]()
			{ 
				// Again UI thread

			}));

	};