Question

I wish in my code to handle the case when the red X at the upper right of the form is clicked. To this end I consulted this and created an event handler thus:-

Private Sub DoFoo (sender As System.Object, e As System.EventArgs) _
                   Handles Me.FormClosing
    ' Do things
End Sub

but I have found (from setting breakpoints) that on certain forms this event handler is not invoked when the red X is clicked, whereas on others it is. The forms are all of type System.Windows.Forms.Form but naturally are different in most respects. Does anyone know what might be causing this and what to do about it?

Edit

In answer to Vitor’s question, the form that isn’t working is created thus:-

If my_form Is Nothing Then
    my_form = New MyForm(parameters)
    my_form.Title = "Contour Plot Options"
Else
    my_form.BringToFront
End If

my_form.Show

Those that are behaving as expected are created like this:-

If my_working_form Is Nothing Then
    my_working_form = New MyWorkingForm
End If

my_working_form.Show

I can’t see any Visible property to set or clear anywhere.

Answer 1

Your parameters aren’t quite right. A FormClosing event has a FormClosingEventArgs argument:

Private Sub DoFoo(ByVal sender As Object, ByVal e As FormClosingEventArgs) _
                  Handles Me.FormClosing
    If (e.CloseReason = CloseReason.UserClosing) Then

    End If
End Sub

You can inspect the e variable for the property `CloseReason’, which would include a UserClosing enum, which means the user closed the form.

Each form should handle its own FormClosing event. Instead of subscribing to the event, I find it better to just override it like this:

Protected Overrides Sub OnFormClosing(ByVal e As FormClosingEventArgs)
  If (e.CloseReason = CloseReason.UserClosing) Then

  End If
  MyBase.OnFormClosing(e)
End Sub