BackgroundDownloader in c++

Question

Hi,

Trying to run a simple file loader, but code crashes at downloadTask.wait( );  Could you help - what is wrong with it?

    Windows::Storage::StorageFolder^ folder = ApplicationData::Current->RoamingFolder;

    String^ file_name = "index.html";

    auto create_file_op = folder->CreateFileAsync( file_name );

    task< StorageFile^ > createFileTask( create_file_op );

    createFileTask.then( [ this ] ( StorageFile^ file )
    {

          BackgroundDownloader^  bd = ref new BackgroundDownloader( );

          DownloadOperation^ loader_op = bd->CreateDownload( ref new Uri("http://www.google.com/index.html"), file );

          task< DownloadOperation^ > downloadTask( loader_op->StartAsync( ) );

          downloadTask.wait( ); 

    } );

Internet capabilities are set.

Answer 1

How about try-catch block.

---

NEU_ShieldEdge

Answer 2

I removed it to show simplified code. try-catch doesn't catch. There are examples of the class use in VB and C#, but none on c++ and apparently there is a difference.

Here is the debugger output:

First-chance exception at 0x754456C4 in StreamSocket.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.
First-chance exception at 0x754456C4 in StreamSocket.exe: Microsoft C++ exception: Concurrency::invalid_operation at memory location 0x02F6CCD0.
First-chance exception at 0x754456C4 in StreamSocket.exe: Microsoft C++ exception: Concurrency::invalid_operation at memory location 0x02F6DA6C.
First-chance exception at 0x754456C4 in StreamSocket.exe: Microsoft C++ exception: Concurrency::unobserved_task_exception at memory location 0x02F6C228.
Debug Error!
Program: ...eamSocket sample\C++\Debug\StreamSocket\AppX\StreamSocket.exe
R6010
- abort() has been called

Answer 3

Here's the C# 'BackgroundTransferDownload' sample coverted to C++/CX:

	Windows::Storage::StorageFolder^ folder = ApplicationData::Current->RoamingFolder;
	String^ file_name = "index.html";
 
	// http://blogs.msdn.com/b/nativeconcurrency/archive/2011/10/27/try-it-now-use-ppl-to-produce-windows-8-asynchronous-operations.aspx

	task<StorageFile^>(folder->CreateFileAsync(file_name, CreationCollisionOption::ReplaceExisting))
		.then([&](StorageFile^ file)
	{
		wchar_t msgbuffer[1024] = {0};
		_swprintf(msgbuffer, L"Created %s\n", file->Name->Data());
		::OutputDebugString(msgbuffer);

		BackgroundDownloader^  bd = ref new BackgroundDownloader( );
		DownloadOperation^ loader_op = bd->CreateDownload( ref new Uri("http://www.google.com/index.html"), file );
		
		task<DownloadOperation^>(loader_op->StartAsync())
			.then([&](DownloadOperation^ opCallback) -> DownloadOperation^
		{
			wchar_t msgbuffer[1024] = {0};
			swprintf(msgbuffer, L"Progress: %s, Status: %d\n", 
				StringFromGuid(opCallback->Guid)->Data(), opCallback->Progress.Status);
			::OutputDebugString(msgbuffer);

			if (opCallback->Progress.TotalBytesToReceive > 0)
            {
                long long percent = opCallback->Progress.BytesReceived * 100 
										/ opCallback->Progress.TotalBytesToReceive;
				swprintf(msgbuffer, L" - Transfered bytes: %I64d of %I64d - %I64d%%\n", 
					opCallback->Progress.BytesReceived, opCallback->Progress.TotalBytesToReceive, percent);
				::OutputDebugString(msgbuffer);
            }
			else
            {
				swprintf(msgbuffer, L" - Transfered bytes: %d\n", opCallback->Progress.BytesReceived);
				::OutputDebugString(msgbuffer);
            }

            if (opCallback->Progress.HasRestarted)
            {
				::OutputDebugString(L" - Download restarted\n");
            }

            if (opCallback->Progress.HasResponseChanged)
            {
                // We've received new response headers from the server.
				swprintf(msgbuffer, L" - Response updated; Header count: %d\n", 
							opCallback->GetResponseInformation()->Headers->Size);
				::OutputDebugString(msgbuffer);
            }

			return opCallback;
		}).then([&](DownloadOperation^ opResponse)
			{
				wchar_t msgbuffer[1024] = {0};
				ResponseInformation^ response = opResponse->GetResponseInformation();
				swprintf(msgbuffer, L"Completed: %s, Status Code: %d\n", 
					StringFromGuid(opResponse->Guid)->Data(), response->StatusCode);
				::OutputDebugString(msgbuffer);
			});
	});

And the debugger output

Progress: {8235A730-26FC-47F7-9118-CB88AA93BE7C}, Status: 5
 - Transfered bytes: 93618 of 93618 - 100%
 - Response updated; Header count: 11
Completed: {8235A730-26FC-47F7-9118-CB88AA93BE7C}, Status Code: 200

-Steve

Answer 4

And the helper function StringFromGuid

Platform::String^ StringFromGuid(GUID guid)
{
	const int bufflen = 40;
	wchar_t guidbuffer[bufflen] = {0};
	::StringFromGUID2(guid, guidbuffer, bufflen);
	return ref new Platform::String(guidbuffer);
}

Answer 5

Thank you very much!