Cannot get an asynchronous operation Result (Windows::Foundation::IAsyncOperation interface) in C++ WinRT

Question

I'm a little bit desperate trying to get the result of a winrt asynchronous method with Windows::Foundation::IAsyncOperation interface. The project is a Visual Studio Community 2017 c++ project with winRT extension enabled. I've tried using std::future / co_await functions and also task method but the call to GetResults() generated always "call at unexpected time" exception.

With the following code I don't get the exception but GetResults() returns nullptr. I have tried also to declare async_op as a shared_ptr auto async_op = std::make_shared<Windows::Foundation::IAsyncOperation<Windows::Devices::Bluetooth::BluetoothLEDevice^> ^> and access to it with *async_op inside the Handler code, but I get the same result.

Any ideas will be welcome.

Thanks in advance.

void BleEnumeration::PerformConnectDevice(std::string* bleDevId)
{               
    std::wstring bleDevId_w_str = std::wstring((*bleDevId).begin(), (*bleDevId).end());
    const wchar_t* bleDevId_w_char = bleDevId_w_str.c_str();
    Platform::String^ bleDevId_refStr = ref new Platform::String(bleDevId_w_char);

    auto async_op = Windows::Devices::Bluetooth::BluetoothLEDevice::FromIdAsync(bleDevId_refStr);
    async_op->Completed = ref new Windows::Foundation::AsyncOperationCompletedHandler<Windows::Devices::Bluetooth::BluetoothLEDevice^>(
        [async_op] (Windows::Foundation::IAsyncOperation< Windows::Devices::Bluetooth::BluetoothLEDevice^ >^ operation, Windows::Foundation::AsyncStatus status)
        {
            if (async_op->Status == Windows::Foundation::AsyncStatus::Completed)
            {
                auto bleDevTest = async_op->GetResults();
            }
        });
}

score 0 · Answer 1 · answered May 24 '18 at 15:03

I made it work:

Windows::Devices::Bluetooth::BluetoothLEDevice^ BleEnumeration::getBleDevice(Windows::Foundation::IAsyncOperation<Windows::Devices::Bluetooth::BluetoothLEDevice^>^ async)
{
    if ((async)->Status != Windows::Foundation::AsyncStatus::Completed)
    {       
        HANDLE signal = CreateEvent(nullptr, true, false, nullptr);
        (async)->Completed = ref new Windows::Foundation::AsyncOperationCompletedHandler<Windows::Devices::Bluetooth::BluetoothLEDevice^>(
            [&signal](Windows::Foundation::IAsyncOperation< Windows::Devices::Bluetooth::BluetoothLEDevice^ >^ operation, Windows::Foundation::AsyncStatus status)
        {
            SetEvent(signal);
        });
        WaitForSingleObject(signal, INFINITE);
    }
    Windows::Devices::Bluetooth::BluetoothLEDevice^ device = async->GetResults();
    return device;
}

bool BleEnumeration::PerformConnectDevice(std::string* bleDevId)
{
    bool success = false;
    Windows::Devices::Bluetooth::BluetoothLEDevice^ bleDevTest = nullptr;

    std::wstring bleDevId_w_str = std::wstring((*bleDevId).begin(), (*bleDevId).end());
    const wchar_t* bleDevId_w_char = bleDevId_w_str.c_str();
    Platform::String^ bleDevId_refStr = ref new Platform::String(bleDevId_w_char);
    Windows::Foundation::IAsyncOperation<Windows::Devices::Bluetooth::BluetoothLEDevice^>^ asyncOp = Windows::Devices::Bluetooth::BluetoothLEDevice::FromIdAsync(bleDevId_refStr);      
    bleDevTest = getBleDevice(asyncOp);

    if (bleDevTest != nullptr)
    {
        success = true;
    }
    return success;
}

And, the reason why GetResults() gave nullptr was this: Enable capability in appxmanifest

All needed capabilities must be enabled in Visual Studio project Package.appxmanifest file, in my case: "Bluetooth". I noticed I was getting error: onecoreuap\drivers\wdm\bluetooth\user\winrt\device\bluetoothledevice.cpp(728)\Windows.Devices.Bluetooth.dll!00007FFC1601AE2F: (caller: 00007FFC1602081A) Exception(1) tid(212c) 80070005 Access is denied.

Cannot get an asynchronous operation Result (Windows::Foundation::IAsyncOperation interface) in C++ WinRT

1 Answers1