Me.FormClosing works on some forms but not others - vb.net

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

Answer 2

If you are instantiating your form you need to remember to AddHandler for the event you want to subscribe to.
my_form = New MyForm(parameters)
my_form.Title = "Contour Plot Options"
AddHandler my_form.Closing, AddressOf MyForm_Closing
'...
Sub MyForm_Closing(s As Object, ByVal e As FormClosingEventArgs)
'...
End Sub
Of course, to avoid memory leaks you should do it like this:
'global code
Private myFormClosingEventHandler As FormClosedEventHandler = Nothing
'...
Private Sub CreateForm
my_form = New MyForm(parameters)
my_form.Title = "Contour Plot Options"
myFormClosingEvent = New FormClosedEventHandler(AddressOf MyForm_Closing)
AddHandler my_form.Closing, myFormClosingEventHandler
'...
End Sub
Sub MyForm_Closing(s As Object, ByVal e As FormClosingEventArgs)
RemoveHandler my_form.Closing, myFormClosingEventHandler
'...
End Sub
Alternatively you can have it all pre-initalized for you by doing this in your class instead:
Private WithEvents my_form1 As Form = New Form()
Private WithEvents my_form2 As Form = New Form()
'... etc.
Now you can add in your code handlers using the Handle keyword as usual without using the AddHandler and RemoveHandler.
Protected Sub my_form1_Closing(s as object, e as FormClosingEventArgs) _
Handles my_form1.Closing
'...
End Sub