Is the BackgroundWorker Completed event performed in background?

Question

Suppose, I make a BackgroundWorker like this

private void RunBackgroundWorker(object sender, DoWorkEventArgs e)
{
    //  Do something lengthy here
    // which takes a lot of time
}
private void BackgroundWorkerCompleted(object sender, RunWorkerCompletedEventArgs)
{
     System.Threading.Thread.Sleep(2000) ; 
     BackgroundWorker1.RunWorkerAsync() ; 
}

I want to ask whether the contents of BackgroundWorkerCompleted function are executed on the "Background" thread or the main UI thread. I am asking this because, I am creating a desktop, app which uses the database and constantly updates it's database after every few seconds

Why don't you run it and find out. You have the code after all. — Servy, Nov 27 '13 at 20:53
If you want to run some code every 2 seconds you should be using a `Timer`, not a BackgroundWorker. — Servy, Nov 27 '13 at 20:54

score 2 · Accepted Answer · answered Nov 27 '13 at 20:55

2

It executes on the UI thread. MSDN explains:

You must be careful not to manipulate any user-interface objects in your DoWork event handler. Instead, communicate to the user interface through the ProgressChanged and RunWorkerCompleted events.

That said, Servy was correct in the comments -- you should be using a Timer for executing code on an interval, not a BackgroundWorker.

answered Nov 27 '13 at 20:55

Daniel Mann

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If there is a lengthy process then it should be put in a BackgroundWorker to prevent freezing the UI. – Rick Hodder Nov 27 '13 at 22:02
@RickHodder The `RunWorkerCompleted` event isn't for long-running processes --it's for updating the UI with the *result* of a long-running process. – Daniel Mann Nov 28 '13 at 00:38

score 1 · Answer 2 · edited May 23 '17 at 12:05

1

I am using BackgroundWorker a lot and can tell that RunWorkerCompleted event is definitely ran in UI thread. Also, you can pass the DoWork result to according eventArgs field and then, in RunWorkerCompleted take it from eventArgs to perform some UI-dependent operations with it, as mentioned here

edited May 23 '17 at 12:05

Community

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answered Nov 27 '13 at 20:57

Is the BackgroundWorker Completed event performed in background?

2 Answers2