VB.NET simpler Async Await example

Well, I couldn’t let this rest, so here is an even simpler example of doing Async Await in VB.NET.

For this example code, I created a simple forms application with two buttons named cmdSynchronous and cmdAsynchronous, a label called lblStatus, and just to demonstrate the UI locking up effect, a combo box with some entries in it. Here is the code behind this form:

Public Class Form1
 
    Sub LongOperation()
 
        Threading.Thread.Sleep(5000)
 
    End Sub
 
    Private Sub cmdSynchronous_Click(sender As Object, e As EventArgs) Handles cmdSynchronous.Click
 
        lblStatus.Text = "Running a long operation synchronously... (UI thread should lock up)"
        Application.DoEvents()  ' needed here so that the label will update
 
        LongOperation()
 
        lblStatus.Text = "Done running the long operation synchronously."
 
    End Sub
 
    Private Async Sub cmdAsynchronous_Click(sender As Object, e As EventArgs) Handles cmdAsynchronous.Click
 
        lblStatus.Text = "Running a long operation asynchronously... (UI thread should be fully responsive)"
 
        Await Task.Run(Sub()
                           LongOperation()
                       End Sub)
 
        lblStatus.Text = "Done running the long operation asynchronously."
 
    End Sub
 
End Class

Notice that both button click events call the LongOperation method, which just sleeps for 5 seconds. However, the synchronous button click will lock up the UI (try to open the combo box, you will see that it waits until the sleep is done before displaying the choice list), whereas the asynchronous one will not.

Now in general, you would probably want to keep the tasks from piling up, as they would if you keep clicking the asynchronous button. I leave this as an exercise to the reader on preventing this problem.

BTW, Happy Birthday to Gary Hoey and Terje Rypdal, two of my favorite guitarists.

3 Comments

  1. android says:

    really nice

  2. Rauf says:

    Its really amazing and simple. Man you are great..

  3. rbcody says:

    Thank you! I’ve been trying to figure out a way for the past several days to modify an existing large project to make a long recursive task asynchronous. This is an incredibly simple solution!

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