How to not duplicate a form?

I'm using the following code to show a form:

VB Code:

Dim frm As New Form1()
frm.Show()

How to not duplicate this form? Instead, I'd like to show the opened one.


Thanks.

Make frm a global variable and use frm.Visible = True/False.

This allows only one instance of the current form :

VB Code:

'allows one instance of the form named Form1
        Static counter As Integer = 0
        If counter = 0 Then
            Dim frm As New Form1
            frm.Show()
            counter += 1
        Else
            Exit Sub
        End If

You can also use this:

VB Code:

Static frm As Form1
If frm Is Nothing Then
  frm=New Form1() 'create
Else
   frm.Activate() 'bring to front
End If

I've been trying the same code Edneeis for many times but still generating new instances . Use Show Method and see how many instances you'll get .:confused:

How about using a shared member in the form? I can't try this out right now, but it should work. One of the problems with using a static (instead of a global) is that instances of the form can be created from other modules or forms.

VB Code:

Shared InstanceCount As Integer
 
Sub New()
    If InstanceCount > 0 Then
        Me.Show
    Else
        InstanceCount += 1
        MyBase.New
    Endif
End Sub

Yeah I forgot the show line, but it worked fine for me. You have to make sure you you call that same procedure everytime to start the form though.

VB Code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Static frm As Form4
        If frm Is Nothing Then
            frm = New Form4 'create
            frm.Show()
        Else
            frm.Activate() 'bring to front
        End If
    End Sub

Should have used Exit Sub, like this...

VB Code:

Shared InstanceCount As Integer
 
Sub New()
    If InstanceCount > 0 Then
        Exit Sub
    Else
        InstanceCount += 1
        MyBase.New
    Endif
End Sub

Quote:

---

Originally posted by Edneeis
Yeah I forgot the show line, but it worked fine for me. You have to make sure you you call that same procedure everytime to start the form though.

VB Code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Static frm As Form4
        If frm Is Nothing Then
            frm = New Form4 'create
            frm.Show()
        Else
            frm.Activate() 'bring to front
        End If
    End Sub

---

Good one, Edneeis, but how to set "frm" to "Nothing" when this form close?

Thanks.

You don't, you just let the GarbageCollector do its thing and take out the garbage. You can still catch any events you need on the form if you have to dispose of anything manually.