Cannot use await in Portable Class Library for Win 8 and Win Phone 8

Question

I'm attempting to create a Portable Class Library in Visual Studio 2012 to be used for a Windows 8 Store app and a Windows Phone 8 app.

I'm getting the following error:

'await' requires that the type 'Windows.Foundation.IAsyncOperation' have a suitable GetAwaiter method. Are you missing a using directive for 'System'?

At this line of code:

StorageFolder guidesInstallFolder = await Package.Current.InstalledLocation.GetFolderAsync(guidesFolder);

My Portable Class Library is targeted at .NET Framework 4.5, Windows Phone 8 and .NET for Windows Store apps.

I don't get this error for this line of code in a pure Windows Phone 8 project, and I don't get it in a Windows Store app either so I don't understand why it won't work in my PCL.

The GetAwaiter is an extension method in the class WindowsRuntimeSystemExtensions which is in System.Runtime.WindowsRuntime.dll. Using the Object Browser I can see this dll is available in the .NET for Windows Store apps component set and in the Windows Phone 8 component set but not in the .NET Portable Subset. I just don't understand why it wouldn't be in the Portable Subset if it's available in both my targeted platforms.

Answer 1

You need the Async targetting pack on NuGet here for async/await to work for that combination of targets.

UPDATE:

Try this (nonsense) code snippet to check if it is using async/await correctly.

public async void MyMethodAsync()
{
    var req = WebRequest.Create("");
    await req.GetRequestStreamAsync();
}

However even if you get past the first problem of async/await not being available, the Package API you are calling is not available in the PCL.