Win8 Bluetooth to device issue: how to invoke DataReader's LoadAsync() repeatedly in a separate data receive thread ?

Question

the code below:

task<String^> CBTWinRTDLL::RecvDataAsync()
{
	if (!CoreApplication::Properties->HasKey("clientSocket"))
	{
		auto op = create_async([]()
		{
		});

		return create_task(op).then([]()
		{
			String^ retStr = "Client socket does not exist, please connect device first.";
			return retStr;
		});
	}

	_reader->InputStreamOptions = InputStreamOptions::Partial;

	task<unsigned int> ReadTask(_reader->LoadAsync(256));
	return ReadTask.then([this](task<unsigned int> readTask)
	{
		try
		{
			int readSize = readTask.get();

			Platform::String^ recvStr;
			if ((readSize) > 0)
			{
				Platform::Array<unsigned char>^ recvArr = ref new Platform::Array<unsigned char, 1>(readSize);
				_reader->ReadBytes(recvArr);
				std::string strHex = toString(recvArr->Data, recvArr->Length);
				recvStr = stops(strHex);
			}
			else
			{
				recvStr = "";
			}
			return recvStr;
		}
		catch (Exception^ ex)
		{
			return ex->Message;
		}
	});
}

The RecvDataAsync() is a method within WinRT DLL and  will be invoked from a metro app,  it can receive data if there are some data in the socket's inputstream after socket connected.  But if BT device doesn't send data , invoke this method will cause a exception at this line:   task<unsigned int> ReadTask(_reader->LoadAsync(256));

My question is:  how to create a separately thread or task to keep monitorring the StreamSocket's inputstream(or any other)  after  bluetooth device is connected or socket->ConnectAsync() is succeeded ?  

what I need is a WinRT DLL method like my code snippet,  it can running asynchronous in workerthread , detect Tcp stream , if there were data sent from BT device , then receive  and  forward to metro app,  otherwize, it should just loopping until user click the stop button in metro app or socket been closed.

---

nio

Answer 1

question 2:  or are there any event for data arriving from bluetooth device by using stream socket , so i can LoadAsync() data and readBytes() in the event handler?   Because i don't know when the data will incomming,  if BT device doesn't send data  and i LoadAsync(),  the exception will raise.

---

nio

Answer 2

Hi nio Pan,

Here is no event for this, you just need to build a loop to check if there is something that you are interested in.

What's your error info? Would you mind sharing it with me?

And also you could have a try on the follow code, maybe it is helpful:

void ListenerContext::ReceiveStringLoop(DataReader^ reader, StreamSocket^ socket)
{
    // Read first 4 bytes (length of the subsequent string).
    task<unsigned int>(reader->LoadAsync(sizeof(UINT32))).then([this, reader, socket] (unsigned int size)
    {
        if (size < sizeof(UINT32))
        {
            // The underlying socket was closed before we were able to read the whole data.
            cancel_current_task();
        }

        unsigned int stringLength = reader->ReadUInt32();
        return task<unsigned int>(reader->LoadAsync(stringLength)).then([this, reader, stringLength] (unsigned int actualStringLength)
        {
            if (actualStringLength != stringLength)
            {
                // The underlying socket was closed before we were able to read the whole data.
                cancel_current_task();
            }
            
            // Display the string on the screen. This thread is invoked on non-UI thread, so we need to marshal the call back to the UI thread.
            NotifyUserFromAsyncThread("Received data: \"" + reader->ReadString(actualStringLength) + "\"", NotifyType::StatusMessage);
        });
    }).then([this, reader, socket] (task<void> previousTask)
    {
        try
        {
            // Try getting all exceptions from the continuation chain above this point.
            previousTask.get();

            // Everything went ok, so try to receive another string. The receive will continue until the stream is broken (i.e. peer closed closed the socket).
            ReceiveStringLoop(reader, socket);
        }
        catch (Exception^ exception)
        {
            NotifyUserFromAsyncThread("Read stream failed with error: " + exception->Message, NotifyType::ErrorMessage);

            // Explicitly close the socket.
            delete socket;
        }
        catch (task_canceled&)
        {
            // Do not print anything here - this will usually happen because user closed the client socket.

            // Explicitly close the socket.
            delete socket;
        }
    });
}

Regards!

Xiaoliang

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