Hi,

I think I may have come across a bug in the FlowChart control, BUT, it might be me!

My app is an MDI application. My parent form creates an instance of the form that contains the flow chart (frmCanvas). When a user closes the frmCanvas form, it first sends an event to the parent form, to allow it disable toolbar buttons etc, and closes.

If you then open a new instance of the frmCanvas form (which contains the flowchart control) and then use the ZoomFactor property, you get a

[code]A first chance exception of type 'System.ObjectDisposedException' occurred in System.Windows.Forms.dll
[/code] on the call to ZoomFactor.

Here is the line of code that generates the error:

[code]
FlowChart1.ZoomFactor = 200 - (_parentForm.cbZoom.SelectedIndex * 10)
[/code]

I have checked, and all variables/objects ARE loaded with real data, they are not 'Nothing' un-initialised etc... FlowChart1 DOES contain an instance of FlowChart. (FlowChart1 sits in the component tray at design time, under the form)

Looks like a prob in the ZoomFactor method... Any ideas?

Regards

Mark.

Hi Stoyan,

Thanks for the suggestion, but sadly, no luck...

Here's the code I was using...

[code]

    Private Sub frmCanvas_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
       RaiseEvent IAmClosing() ' tell the parent form that this form is closing
       RemoveHandler _parentForm.LoadProject, AddressOf Me.LoadProject ' remove handler
       RemoveHandler _parentForm.SaveProject, AddressOf Me.SaveProject ' remove handler
       _parentForm.lblStatus.Text = "Project closed"   ' Text for parent forms Status bar (at bottom of form)
       _parentForm.ProjectInMemory(False)  ' flag to tell parent form that there is no project in memory
       FlowChart1.Dispose()    ' kill the flowchart object on this form
    End Sub
[/code]

Any other ideas?

Regards

Mark.

Quote:


Are there any event handlers in the child form attached to events of the parent form UI? If so, try detaching them (RemoveHandler keyword in VB.NET) when a child form is closed. Otherwise the .NET form object might still be live even if the OS window is destroyed. Event handler invoked on such a closed form will lead to that exception.

Stoyan

I think I should also say that there are other combo boxes on the parent form to do other things, such as set line types, and arrow head sizes. These work in EXACTLY the same was as Zoom: i.e. they raise an event which is captured by frmCanvas and processed. These work fine. ONLY the ZoomFactor is a problem. This is why I suspect it may be a problem with the FlowChart DLL.

Hope this info is of use.

Mark.

Are you removing all event handlers, including the ones for the zoom combo box? Otherwise your child forms will never be freed by the Garbage Collector, since having an attached event is a valid reference to an object.

Just to test this, remove the code that throws an exception from the zoom combo handler (i.e. setting the ZoomFactor) and add some counter variable there. Then open and close child forms several times, leaving just one on the screen in the end. Now change the zoom level from the combo box - if everything is ok, the counter should increment just once. If the closed forms are still referenced through an event handler, the counter will increment more than once.

Getting an exception from the ZoomFactor setter, but not from other properties, might be related to the fact that ZoomFactor sets some properties of the flowchart's scrollbars. The scrollbars are child controls themselves and their window handles might be already destroyed.

Stoyan

Stoyan,

I just wanted to post back and say thank you for your help. It was much appreciated.

The problem was with MY code, and NOT with the FlowChart.Net component, which works fine.

The problem was simple (they always are, eh?):

My main (MDI parent) form creates a child form which houses the FlowChart

The child form also creates a reference to the main form, so that methods etc on the main form can be called from the child form.

When the child form closed, it correctly removed the event handlers, but I forgot to change the main form reference to nothing.

DOH!

This was a horrible bug to find! The problem is that I am working on this program in my spare time and I sometimes struggle to remember what does what, and forget where to find things!

Anyway, that problem is fixed now.

THANKS FOR YOUR HELP, Stoyan