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//*********************************************************
//
// Copyright (c) Microsoft. All rights reserved.
// This code is licensed under the MIT License (MIT).
// THIS CODE IS PROVIDED *AS IS* WITHOUT WARRANTY OF
// ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING ANY
// IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR
// PURPOSE, MERCHANTABILITY, OR NON-INFRINGEMENT.
//
//*********************************************************
#pragma once
namespace SDKTemplate
{
namespace DeviceHelpers
{
// We use a DeviceWatcher instead of DeviceInformation.FindAllAsync because
// the DeviceWatcher will let us see the devices as they are discovered,
// whereas FindAllAsync returns results only after discovery is complete.
//
// The convertAsync functional is passed a device ID (Platform::String^) and returns a
// Concurrency::task<Something^>.
template<typename Converter>
auto GetFirstDeviceAsync(Platform::String^ selector, Converter convertAsync)
-> decltype(convertAsync(nullptr))
{
using T = typename decltype(convertAsync(nullptr))::result_type;
Concurrency::task_completion_event<T> completionEvent;
auto pendingTasks = std::make_shared<std::vector<Concurrency::task<void>>>();
Windows::Devices::Enumeration::DeviceWatcher^ watcher = Windows::Devices::Enumeration::DeviceInformation::CreateWatcher(selector);
watcher->Added += ref new Windows::Foundation::TypedEventHandler<Windows::Devices::Enumeration::DeviceWatcher^, Windows::Devices::Enumeration::DeviceInformation^>(
[completionEvent, pendingTasks, convertAsync](Windows::Devices::Enumeration::DeviceWatcher^ sender, Windows::Devices::Enumeration::DeviceInformation^ device)
{
auto task = convertAsync(device->Id).then([completionEvent](T t)
{
if (t != nullptr)
{
completionEvent.set(t);
}
});
pendingTasks->push_back(task);
});
watcher->EnumerationCompleted += ref new Windows::Foundation::TypedEventHandler<Windows::Devices::Enumeration::DeviceWatcher^, Platform::Object^>(
[completionEvent, pendingTasks](Windows::Devices::Enumeration::DeviceWatcher^ sender, Platform::Object^ args)
{
// Wait for completion of all the tasks we created in our "Added" event handler.
Concurrency::when_all(pendingTasks->begin(), pendingTasks->end()).then([completionEvent]()
{
// This sets the result to "nullptr" if no task was able to produce a device.
completionEvent.set(nullptr);
});
});
watcher->Start();
// Wait for enumeration to complete or for a device to be found, whichever comes first.
return Concurrency::create_task(completionEvent).then([watcher](T result)
{
watcher->Stop();
return result;
});
}
}
}
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