Question

I’m working with BackgroundWorker, I want the BackgroundWorker do the retrieval process of data from database while the user can still do another task on the form. The problem is, after retrieving the data, I can’t seem to access the ListView in my Form from the DoWork event of BackgroundWorker, I will populate that ListView using the data I’ve retrieved. What should I do? Am I missing something?

Consider this example, this is how I’m doing it:

Public Class Test
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        BackgroundWorker1.RunWorkerAsync()
    End Sub

    Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Label1.Text = "Hello World"
    End Sub
End Class

Answer 1

The documentation for BackgroundWorker is quite clear:

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.

---

The sample “How to: Download a File in the Background” shows one example way that objects can be shared between the main thread and the background worker – by arranging for such objects to be stored in variables at the class level.