how to prevent multiple instances of 2nd form?

[Guest]

Hello,

my app opens a 2nd form (form2) by clicking a button on the first form
(form1). I do not want to open form2 in modal form, but I only want one
instance of form2 open. So if someone re-clicks the button on form1 there
will not be multiple instances of form2. I created a module level boolean
var in form1 and a property in form1 to control the loading of form2, but I
am having a problem resetting the value of this boolean var. Here is what I
have:

'--in form1 I have this property

Public Property frmLoaded() As Boolean
Get
Return bFrmLoaded
End Get
Set(ByVal Value As Boolean)
bFrmLoaded = Value
End Set
End Property

Sub...
If bFrmLoaded.Equals(False) Then
form2.Show
bFrmLoaded = True
End If
....
End Sub

In form2 in the closing event I want to reset the value of bFrmLoaded to
False. But when I set a form var to form1 - it is a new instance of the form
Dim frm As New form1
frm.frmLoaded = False

The original form1 does not receive this. I can't remember how I dealt with
this in the past. I have done this before. Just can't remember what I did.
Or is there a better approach to dealing with keeping only one instance of a
form (which is not in modal form or mdi, etc)?

Any suggestions appreciated on how to reset the form1 bFrmLoaded boolean
var from form2.

Thanks,
Rich

 

[Cyril Gupta]

Hmm...

Well your strategy is not going to work, because very act of accessing the
variable will create a new instance of the form.

This is what you should do, and it's damn easy

Dim frm as New Form1

If frm Is Nothing Then
Frm.show
End If

Regards
Cyril Gupta

 

[Cor Ligthert [MVP]]

Rich,

It is a very well hidden property.

You can use the Isdisposed from the form2.

http://msdn2.microsoft.com/en-us/library/system.windows.forms.control.isdisposed.aspx

If this answer is not enough, than reply, however I assume it is enough,

Cor

 

[Guest]

OK. I found this code snippet that seems to work for my purposes:

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button2.Click
' If the instance still exists... (ie. it's Not Nothing)
If Not IsNothing(F2) Then
' and if it hasn't been disposed yet
If Not F2.IsDisposed Then
' then it must already be instantiated - maybe it's
' minimized or hidden behind other forms ?
F2.WindowState = FormWindowState.Normal ' Optional
F2.BringToFront() ' Optional
Else
' else it has already been disposed, so you can
' instantiate a new form and show it
F2 = New Form2
F2.Show()
End If
Else
' else the form = nothing, so you can safely
' instantiate a new form and show it
F2 = New Form2
F2.Show()
End If

End Sub

But if anyone has any other or additional suggestions - please share.

Thanks

 

[Cyril Gupta]

Hello Rich,

I think it is a perfectly valid solution.

Note that it combines what Cor and I suggested

If you check for IsDisposed without checking for Is Nothing first, you will
get an error, or will create an instance of the form.

Regards
Cyril Gupta