Portable class library equivalent of Dispatcher.Invoke or Dispatcher.RunAsync

Question

In .NET, Windows 8 and Windows Phone 7 I have code similar to this:

public static void InvokeIfRequired(this Dispatcher dispatcher, Action action)
{
    if (         


        

Answer 1

You can use SynchronizationContext.Post or Send method. It is portable, and when you use a UI framework with a dispatcher then the current synchronization context will delegate the work to the Dispatcher.

Specifically, you can use the following code:

void InvokeIfRequired(this SynchroniationContext context, Action action)
{
    if (SynchroniationContext.Current == context)
    {
        action();
    }
    else
    {
        context.Send(action) // send = synchronously
        // context.Post(action)  - post is asynchronous.
    }  
}

Answer 2

With the advent of the TPL. I came up with a slightly improved version of the accepted answer which returns a task and can be await'ed using the new async and await keywords.

public Task RunAsync(Action action)
{
    TaskCompletionSource<object> taskCompletionSource = new TaskCompletionSource<object>();

    if (this.synchronizationContext == SynchronizationContext.Current)
    {
        try
        {
            action();
            taskCompletionSource.SetResult(null);
        }
        catch (Exception exception)
        {
            taskCompletionSource.SetException(exception);
        }
    }
    else
    {
        // Run the action asyncronously. The Send method can be used to run syncronously.
        this.synchronizationContext.Post(
            (obj) => 
            {
                try
                {
                    action();
                    taskCompletionSource.SetResult(null);
                }
                catch (Exception exception)
                {
                    taskCompletionSource.SetException(exception);
                }
            }, 
            null);
    }

    return taskCompletionSource.Task;
}