asked on

Thread Safe Calls

I have a progress bar set to marquee on an mdi parent status bar. To make it run smoothly and continuously while updating I thought it may be time to try somehting new rather than Application.DoEvents.

So I have a procedure in a child form which is called by the following

....enable the progress bar

Dim newthread As New Threading.Thread(AddressOf MyProcedure)
newthread.Start()

The procedure fills a datatable from various tables, then a DataView which is sorted, which is then used to populate a DataGridView control. I have found out that (via debug message) I have to check the DataGridView.InvokeRequired property when i try to set the DataGridView datasource, and then do something else if the answer is True, when doing something to a control not invoked by the same thread. I am not sure what code I need if the answer is true.

so..

Private Sub MyProcedure()

....do some stuff

If MyDataGridView.InvokeRequired Then

......WHAT GOES HERE

else

MyDataGridView.DataSource = MyDataView

End If

'Disable progress bar
me.cursor = cursors.default
MyMdiParent.ProgressBar.Enabled=false

PS. I have also discovered i will get the same problem when i try to reset the cursor for the form back to default and also try to disable the progress bar as they were set on different threads

End Sub

I am assuming of course this is the way to go for smoothly operating progress bars

SOLUTION

doraiswamy

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JeffvClayton

ASKER

Yes i do you want the progress bar in the background, marquee-ing smoothly, but I do not want to create a new form, i have a progress bar in a status strip at the bottom of an Mdi parent which is in the original thread, I want to use that. Does it mean i basically have to add the progress bar to the status strip at runtime? Or can i manage the invokerequired properties as suggested by microsoft?

doraiswamy

I'm not sure about the "invokerequired" property. You can try creating a progress bar at runtime and accessing it from the thread.

JeffvClayton

ASKER

OK, that is something to try.

I have also tried this as the last line in the procedure with no error messages, but no data in the DataGridView either!

MyDataGridView.Invoke(MyDataGridView.DataSource, MyDataView.ToTable)

doraiswamy

Sorry, in the earlier post I meant create a progress bar at design time, not runtime

ASKER CERTIFIED SOLUTION

DjDezmond

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JeffvClayton

ASKER

I have solved the problem, you cant change an object from a different thread, you need all this....

Instead of 'MyDataGridView.DataSource = MyDataView' as the last line of the procedure in the new thread

you need a new procedure call as the last line e.g. PassNewDataView(MyDataView.ToTable)

End Sub
'Another sub which runs in the new thread
'--------------------------------------------------
Sub PassNewDataView(ByVal MyDataView As DataTable)
Me.BeginInvoke(New DelegateUpdateSource(AddressOf Me.ChangeSource), New Object() {MyDataView})
End Sub

' then a new Delegate Sub as this....
' ----------------------------------------
Public Delegate Sub DelegateUpdateSource(ByVal DV As DataTable)

'Finally a sub which runs in the original thread to change the datasource and stop the progress bar
'-----------------------------------------------------------------------------------------------------------------

Sub ChangeSource(ByVal DV As DataTable)

Me.MyDataGridView.DataSource = DV

Me.Cursor = Cursors.Default
MParent.PB1.Enabled = False

End Sub

Thanks anyway

Jeff

JeffvClayton

ASKER

Thanks Dez, I was typing as you sent the message.

DjDezmond

I would of typed it a hell of a lot sooner (just as you posted the msg) but i was on my phone the whole time! Sorry mate!

Glad its working now anyway.

Cheers,

Dez

DjDezmond

one more thing...

Sub PassNewDataView(ByVal MyDataView As DataTable)
Me.BeginInvoke(New DelegateUpdateSource(AddressOf Me.ChangeSource), New Object() {MyDataView})
End Sub

There is no need for a seperate sub here... you can just call:

Me.BeginInvoke(New DelegateUpdateSource(AddressOf Me.ChangeSource), New Object() {MyDataView})

... from anywhere on the thread

Cheers,
Dez

JeffvClayton

ASKER

Even Better!

Thanks Dez.