Still not getting how to return a value from BackgroundWorker

Question

I have a simple BackgroundWorker that should generate results, but I don't know how to get them back to my calling method. I have read a number of answers, and they all show me how the RunWorkerCompleted event can receive the results of the DoWork event handler, and to prove this they show a message box with the result. That's all good, but how do I get a result back to the actual method that called RunWorkerAsync ?

myResult=myBackGroundWorker.RunWorkerAsync(); // This obviously doesn't compile

This answer in particular has been very useful:

How to make BackgroundWorker return an object

but I still don't know how to access the results. This answer also mentions the use of a delegate:

BackgroundWorker Return A Value?

but I don't understand if this would solve my problem, or if I would still just get the result inside the RunWorkCompleted event handler.

Answer 1

Short answer: you can't.

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Think about what it means to return the value back to the method that called RunWorkerAsync . This would mean that the method has to pause its execution, wait for the background worker to complete its work, then continue again. But you still want other methods to run during the waiting, otherwise the UI would freeze.

Does that sound familiar to you? That's basically what an async method does when it encounters an await expression!

BackgroundWorker is quite an old API, and there wasn't the fancy feature of async/await when it came out (async/await is a language feature anyway), which is why it uses events to do the trick. Back then, there wasn't a way to do an operation asynchronously, and return a value back to the caller elegantly.

Now that we have async/await, you can use it to do what you want:

someReuslt = await Task.Run(() => { ... });

If you haven't heard about async/await at all, this is a good place to start.