preventing 2 instances of the same form

[levogiro]

hi,

i'm developing an MDI application and i'd like to open just one instance of a form. i tried the code below and it works when the form is loaded for the first time, but if i close the form and try to open it again i receive this error message: CANNOT ACCESS A DISPOSED OBJECT NAMED "frmUsuario".

Dim fUsuario As frmUsuario

Private Sub mniUsuario_Click(ByVal sender As 
                             System.Object, 
                             ByVal e As System.EventArgs) 
            Handles mnuUsuario.Click

    If fUsuario Is Nothing Then
        fUsuario = New frmUsuario
    End If

    fUsuario.MdiParent = Me
    fUsuario.Show()

End Sub

thanks,

benedito.

 

[chrissie1]

I would do it another way.
this in the closing event of frmusuario

e.cancel = true
me.tag = "Hide" 
me.hide

and then replace your code with this.

Dim fUsuario As new frmUsuario

Private Sub mniUsuario_Click(ByVal sender As 
                             System.Object, 
                             ByVal e As System.EventArgs) 
            Handles mnuUsuario.Click

    If fUsuario.tag <> "Show" Then
        fUsuario.tag = "Show"
        fUsuario.MdiParent = Me
        fUsuario.Show()
    End If


End Sub

Christiaan Baes
Belgium

If you want to get an answer read this FAQ faq796-2540
There's no such thing as a winnable war - Sting

 

[JohnYingling]

Try using IsDisposed. You MUST use OrElse rather than Or.
if fUsuario Is Nothing OrElse _
fUsuario.IsDisposed Then

http://www.VBCompare.com

Compare Code

 

[levogiro]

actually, i did this way...it's working, but i don't like to see my form wandering in the MDI form every time i load it...i'd like to know if there's a way to avoid this.

    Dim fUsuario As frmUsuario

    Private Sub mniUsuario_Click(ByVal sender As
                                 System.Object,
                                 ByVal e As 
                                 System.EventArgs)
                Handles mnuUsuario.Click

        If Not fUsuario Is Nothing Then
            fUsuario.Close()
        End If

        fUsuario = New frmUsuario
        fUsuario.MdiParent = Me
        fUsuario.Show()

    End Sub

 

[levogiro]

JohnYingling,

i tried your code and it worked fine, thanks a lot...but everytime i load the form it appears at a different place in the MDI form. it there a way to avoid this ?

again, thanks.