You can make an event handler async by using the async keyword, but the handler will immediately return upon the first await statement. Asynchronous methods are non-blocking methods for a very good reason. They simply pause execution whenever there is an await and resume execution once the awaited task completes, but the method itself immediately returns to the caller in order to free up the UI thread. 

So, in principal this is how you would write such an event handler if the control has means to let it know when you are done.

public async void SomeEventHandler(object sender, SomeEventArgs args)

{

     await SomeAsyncMethod();

     args.Done();   // Provided there is such a thing for this event

}

Now having said that, you can block the UI thread while waiting for a task to complete, but you shouldn't do that. Blocking the UI defeats the whole point of asynchronous programming in the first place. 

public void SomeEventHandler(object sender, SomeEventArgs args)

{

     SomeAsyncMethod().Wait();   // Block thread until task completes, but really don't do this ever!!!!!

}

 

I am looking for advice on how to perform Async functions (i.e. Saving or Querying) within an event handler of a UI control. For example, I have a gridview and I need to perform validation and saving of a specific row before the user can move off the row.

 

The problem is that the async calls start and execution continues with the rest of the method and exits before the async method actually completes. There may be times when a validation error occurs during the save and I want to prevent focus from leaving the row but since the grid has already allowed the user to move focus, it's too late to move it back.  

 

A lot of event handlers have a way to signal back or return something to the sender to indicate succss or failure of an event (i.e. cancel a click event or something like that).

 

So how can I perform a async call in an event handler and get the response back from the async method before exiting the handler?

 

Thanks!