Suddenly the Form.Shown event doesn't fire anymore

dilkonika

I have a vb.net 2013 project. I have a form with a lot's of controls. Everything was working perfectly. But at some point , I don't know what I have done , but the Form.Shown event doesn't fire anymore. The form is open correctly and everything works , except that Event. I delete and recreated again this event , but doesn't work. what may be the cause and what I should do to fix this ? Thank you !

CHill60

Do you mean it doesn't fire ever? Or only the first time the form is shown and then not fired after that

dilkonika

I mean doesn't fire ever.

CHill60

Does your Shown event handler definitely have Handles MyBase.Shown after it?

dilkonika

Of course. Was working before. I think I found that the cause of the problem is this line of code in Load event :

Application.AddMessageFilter(filter1)

where filter1 is a IMessageFilter. This filter prevent users clicking on a specific form's area when a condition is true. When I remove this line of code , the shown event is fired. But what has to do this with a form shown ???!!! And why on other forms ( where I have also exactly this line of code ) everything is working perfectly ?

Richard Deeming

Post the code for your IMessageFilter implementation.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

dilkonika

Imports System.Windows.Forms
Public Delegate Sub InsideDelegate(ByRef value As Boolean)
Public Class MyMessageFilter
Implements IMessageFilter

Public Event Inside As InsideDelegate

Private Const WM\_LBUTTONDOWN As Integer = &H201
Private Const WM\_LBUTTONUP As Integer = &H202
Private Const WM\_PAINT As Integer = &HF


Public Function PreFilterMessage(ByRef m As Message) As Boolean Implements IMessageFilter.PreFilterMessage
    If m.Msg = WM\_PAINT Then
        Return False
    End If

    Return OnInside()

End Function

Private Function OnInside() As Boolean
    Dim \_inside As Boolean = True

    If InsideEvent IsNot Nothing Then
        InsideEvent(\_inside)
    End If

    Return \_inside
End Function

End Class

Richard Deeming

So either InsideEvent is Nothing, or it's setting the parameter to True, and your IMessageFilter is cancelling every message except WM_PAINT. You've declared constants for WM_LBUTTONDOWN and WM_LBUTTONUP; did you intend to test for and cancel those specific messages?

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

dilkonika

yes , I was thinking to test something before.

dilkonika

Any solution ?

Richard Deeming

Yes - don't cancel every message sent to your form. :doh: Most Windows Forms events are raised in response to window messages. If you cancel all messages being sent to the form, then you shouldn't be surprised when things stop working as expected.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

dilkonika

Sorry , but the filter became active only when a condition is true. This condition became true only if the user press a button. But the user can't press a button when the form is not shown. so before the form is shown , the filter has no effect.

Richard Deeming

When you add the filter in the form's Load event, you prevent any further messages from being sent to the form. (As I said before, either InsideEvent is Nothing, or it's setting the parameter to True.) That prevents the form from receiving the message telling it that it has been activated, which prevents it from raising the Shown event. Adding a filter which prevents any window messages from being sent to your form is a very bad idea. You should not be surprised when it breaks things in interesting ways!

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

dilkonika

Private Sub filter_Inside1(ByRef value As Boolean)
value = condition1
End Sub

Dim condition1 as Boolean=false

On form's load event :

AddHandler filter1.Inside, AddressOf filter_Inside1
Application.AddMessageFilter(filter1)

As you can see at the beginning the filter is not active because the value=false. And I repeat , that I have this scenario in all my forms , but only this form has the problem.

Richard Deeming

Then there's something else going on that you haven't shown us. It's still a very bad idea to cancel all window messages for a form. Your filter should only be cancelling the specific messages that you want to block.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

dilkonika

If it was something else , why the problem is resolved when I remove the line of code that add the filter to application ? And just to clarify , I doesn't cancel all messages to the entire form. The condition that enable/disable the filter become true only if some other conditions are true and if the user click with mouse in some specific area.

Richard Deeming

Since I can't see your screen, access your hard-drive, or read your mind, the only information I have available is what you have posted in this thread. Based on that information, there are two possibilities:

The filter is active when the form is loaded, which means you are cancelling every message being sent to the form;
The filter is not active when the form is loaded, and something else which you haven't shown us is happening on that specific form;

If removing the filter fixes the problem, then I'm inclined to think it's #1. However, since you keep insisting that the filter is not active when the form is loaded, then that only leaves #2. Finding the real cause of the problem will involve debugging your code. YOU are the only person who can do that.

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer