[RESOLVED] Close a child form of MDI Form on Load

[sapator]

Hi.
I'm on a tricky situation here.

I need to close a child form of MDI, if the form has an error when Loading.
Apparently this cannot be done inside the Load event of the child form ( as me.close() ).
I though about closing in the _show event but since the form is async, the event fires before load completes.
Moving all the code from the Load event is quite difficult.
So any opinions?

What I am going to do if I can't figure this out is setting a global parameter on the Mdi form when child completes load. If it is true, do nothing, if false, then close the child, but I'm wondering if there is a solution for fix this strictly on the child form.

Thanks.

[jmcilhinney]

This worked for me:

Public Class Form2
 
    Private work As Task
 
    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        work = DoWorkAsync()
    End Sub
 
    Private Async Sub Form2_Shown(sender As Object, e As EventArgs) Handles Me.Shown
        Try
            Await work
        Catch
            Close()
        End Try
    End Sub
 
    Private Async Function DoWorkAsync() As Task
        Await Task.Delay(TimeSpan.FromSeconds(5))
 
        Throw New Exception("Boom!")
    End Function
 
End Class

The form was displayed but then closed automatically after 5 seconds. In fact, this also worked:

Public Class Form2
 
    Private Async Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Try
            Await DoWorkAsync()
        Catch
            Close()
        End Try
    End Sub
 
    Private Async Function DoWorkAsync() As Task
        Await Task.Delay(TimeSpan.FromSeconds(5))
 
        Throw New Exception("Boom!")
    End Function
 
End Class

[sapator]

HI JMC.
Well the Load has async and normal tasks.
Again the issue only happens on child forms of MDI.
Maybe the issues is that the Load is not Declared as async but I prefer your first example, I will try to push all of my async code to the _shown part of the form and see if I have any luck doing so.
Thanks

Edit:
The load form was actually declared as async, so the closing calls should have worked but they don't also, moving on _Show did nothing.
There may also be a problem with controls changing values inside the async. I have a global catch function on the application events but it does not catch anything.

So as I would be having to take a look at roughly 10k lines of code, I just went to plan B and inserted a value - to be deleted - on the main MDI form that do a light swipe every 5 second and clear any crashed forms.

[.paul.]

You don't need to be looking to close crashed forms. The correct way is to avoid the crashes properly...

[sapator]

Yess, but...

I'm using remote WMI calls on old computers. Sometimes WMI will just crash. That is not my fault and I can't do anything about it, except maybe dump the computers.

[jmcilhinney]

I think "crash" is probably an inaccurate term in this case. A crash is an unhandled exception. I think that what .paul. is suggesting is that you handle the exceptions appropriately, but I expect that that is already what you're doing and you want to close the form when you catch such an exception. Throwing an exception is not crashing. Failing to catch an exception that is thrown is crashing.

[sapator]

Yes, correct.
Unfortunately there is not much I can do when WMI crashes but just catch it.
Also I tried using something similar to this code on apllicationevent so I maybe could catch the exception there and close the from from this class but I does not really catch any exception at all.
Maybe I haven't written something correctly but, for now a timer seems to work:

If you're interested to take a look:

  Private Delegate Sub SafeApplicationThreadException(ByVal sender As Object,
        ByVal e As Threading.ThreadExceptionEventArgs)

        Private Sub ShowDebugOutput(ByVal ex As Exception)

            'Display the output form


            'Perform application cleanup
            'TODO: Add your application cleanup code here.

            'Exit the application - Or try to recover from the exception:
           'Form close attempt... or
           ' Environment.Exit(0)

        End Sub

        Private Sub app_ThreadException(ByVal sender As Object,
    ByVal e As Threading.ThreadExceptionEventArgs)

            'This is not thread safe, so make it thread safe.
            If MainForm.InvokeRequired Then
                ' Invoke back to the main thread
                MainForm.Invoke(New SafeApplicationThreadException(AddressOf app_ThreadException),
            New Object() {sender, e})
            Else
                ShowDebugOutput(e.Exception)
            End If

        End Sub

        Private Sub AppDomain_UnhandledException(ByVal sender As Object,
    ByVal e As UnhandledExceptionEventArgs)

            ShowDebugOutput(DirectCast(e.ExceptionObject, Exception))

        End Sub

        Private Sub MyApplication_UnhandledException(sender As Object,
                                             e As ApplicationServices.UnhandledExceptionEventArgs) Handles Me.UnhandledException
          
            ShowDebugOutput(e.Exception)

        End Sub

[sapator]

Just to add that there was another problem that async load was crashing.
When I used just exit sub inside an async statement, the whole app would crash.
The issue was that exiting a loading form when async tasks took place, just did not go well with it.
I've googled but did not find anything, thankfully I've struggled a lot with async cancellations last month so my idea was to use a Task.WaitAll() just before the exit sub.
Again exit SUB not CLOSE() . That did the trick. And that is only necessary on Loading the form. On any other function included an identical function that has almost all the form_load code it does not need to use Task.WaitAll().
Possible it would have worked with a cancellation token also but I did not try it.
So, I would have to say, go figure and good riddance.