VB.NET 2005 Multithreading / Cross threading operation not valid

[hugh999]

Hi
I am trying to introduce Multithreading in to my program so that the program remains responsive but am getting the error Cross threading operation not valid.

My program will execute a batch file on a list of files that I have added to a ListBox. When the batch file finishes working on the first file in the list box I would like the program to increment a number on a label to show that the batch file has finished working on the file and then move on to the next file in the ListBox.

Here is the code I am working with under a button control:

Dim t As Threading.Thread
t = New Threading.Thread(AddressOf Me.Test1)
t.Start()

Here is the code I have under the Test1 sub:

Dim i As Integer
For i = 0 To ListBox1.Items.Count – 1
oWrite = IO.File.CreateText("c:\verify.bat")
‘Btach file commands
oWrite.Close()

Dim p As Process = New Process
p.StartInfo.FileName = ("c:\verify.bat")
p.StartInfo.UseShellExecute = False
p.StartInfo.CreateNoWindow = True
p.Start()
p.WaitForExit()

Dim down As Integer = Label5.Text + 1
Label5.Text = down
Label5.Refresh()
            
Next

I have been looking on the net and trying my hand at few examples but getting no where. Does anyone know of how are where I need to add cross threading code so that I can add a value to the label; control.

Thanks for your help

 

[chrissie1]

You need this in a separate function

private delegate setlabeldel()

private function setlabel()
  if label5.invokerequired then
    me.invoke(new setlabeldelegate(addressof setlabel,new object() {})
  else
    Dim down As Integer = Label5.Text + 1
    Label5.Text = down
    Label5.Refresh()
  end if
end function

Yhis code is untested so bound not to work, if it does then good for you.

Christiaan Baes
Belgium

My Blog

 

[hugh999]

Thanks for the code. I copied it to my form but am getting the message Sub or Function expected after "delegate" for the line private delegate setlabeldel()

Is there a specific location where i should copy the code to.

Thanks

 

[chrissie1]

because it should be

private delegate function setlabeldel()

Christiaan Baes
Belgium

My Blog

 

[hugh999]

Hi

I have declared it as a function private delegate function setlabeldel() but the line me.invoke(new setlabeldelgate(addressof setlabel,new object() {})is telling me that the text setlabeldelgate is not defined

I appreciate your help

 

[chrissie1]

I think you could have figured that one out by yourself but here goes.

me.invoke(new setlabeldel(addressof setlabel,new object() {})

Christiaan Baes
Belgium

My Blog

 

[hugh999]

Hi

I have tried a few scenarios with the code but am getting the message
Setlabeldel is a delegate type and requires a single ‘addressof’ expression as the only argument to the constructor for the line of code me.invoke(new setlabeldel(addressof setlabel,new object() {})

 

[chrissie1]

Ok I was close.

me.invoke(new setlabeldel(addressof setlabel),new object() {})

very close.

Christiaan Baes
Belgium

My Blog

 

[hugh999]

Hi Christiaan

Thanks for your help with this. One last question, where in my code should i copy this fucntion to or where in my code should i call the function.

Thanks

 

[hugh999]

It is OK, i discoverd where to call the function from.

Thanks for your help