Asynchronously invoke a lambda and invoke a callback lambda upon completion back on the main thread. Helpful in the event you're unable to enjoy TPL or async/await.

async_lambda_with_callback.cs

using System.Runtime.Remoting.Messaging;
using System.Threading;

// capture the ui thread context for completion callback
private SynchronizationContext context = SynchronizationContext.Current;

Action action = () => {
	/* do some stuff */
};
    	
Action<IAsyncResult> complete = (result) => {
	try
	{
		Action caller = (Action)((AsyncResult)result).AsyncDelegate;
		caller.EndInvoke(result);
		
		context.Post(state => {
			/* do this stuff back on main thread */
		}, null);
	}
	catch (Exception ex)
	{
		/* do some error handling */
	}
};

action.BeginInvoke(new AsyncCallback(complete), null);