textbox text not Updating while for each loop running

Question

Windows Forms, VB application... Forgive me in advance for this very elementary question but I am overlooking something really simple here. I would like to have a label show the current value of a variable as the for each loop runs.. I created a very simple Button Click event to figure out where its failing. As it is right now the value does not display until after the for each loop finishes running, which it should actually display the counter value each time it runs through... I know this is possible and really simple because I did it years back but for the life of me cant figure out why I am missing the bar as it should constantly update the label to reflect that? Test Sub is as follows:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim counter As Integer = 0
    For x As Integer = 1 To 200000
        counter += 1
        Label1.Text = Convert.ToString(counter)
    Next
End Sub

Add Label1.Update(). That will work for about 5 seconds until Windows puts a stop to it. — Hans Passant
– Hans Passant, Commented Mar 8, 2012 at 4:11

Akhilesh B Chandran · Accepted Answer · 2012-03-08 03:34:10Z

5

Try adding the line: Application.DoEvents() inside the loop.

answered Mar 8, 2012 at 3:34

Akhilesh B Chandran

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2 Comments

codechurn Over a year ago

This definately answers the question, however if you are using DoEvents you should also consider the fact that it opens up the possibility of the user interacting with the UI in ways you may not have expected. For example, the user can close the form while the loop is running, they can click on buttons (which can be especially interesting if a button triggers your loop in the first place). It has a purpose, but you are better served by not running long operations on the UI thread.

Miro J. Over a year ago

Have in mind that DoEvents will slow down the actual execution of your loop. Things like these are usually executed in other threads, while releasing the GUI thread. Check out the BackgroundWorker as well.

John Woo · Accepted Answer · 2012-03-08 03:40:14Z

1

try this

For x As Integer = 1 To 200000
    counter += 1
    Label1.Text = Convert.ToString(counter)
    System.Threading.Sleep(200)
Next

I would advise you to use BackGroundWorker if you want to have a report progres.

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edited Mar 8, 2012 at 3:40

answered Mar 8, 2012 at 3:33

John Woo

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