[02/03] Open Varible Named Form

[JesseH]

I am trying to open a form using varible names. I can not get it to work.

Dim wInvItemSelected As String
Dim wIndex As Integer
wIndex = lstInvInqSelect.SelectedIndex
Dim WFormName As String
WFormName = Trim(InvMenusForm(wIndex))
Dim objNewForm As Object = Activator.CreateInstance(Type.GetType(WFormName)) <==== Error Here
Dim frm As Form = DirectCast(objNewForm, Form)
frm.Show()


The error is shown on a message box "Microsoft Development Enviroment"

an unhandled exception of the 'System.argumentnullexception' occurred in mscorlib.dll

Additional Information: Value cannot be null

I can not find the error, can anyone help.

Thanks in advance.

[.paul.]

why do you need a form with a variable name?

[Nerd44]

I suppose, the name of the type is not correct and full qualified.
if possible, put System.Type-Items into ur listbox and set listbox.DisplayMember to "Name".
then u can go like

Dim objNewForm As Object = Activator.CreateInstance(Directcast(lstInvInqSelect.SelectedItem, System.Type))

and there is not to worry about wrong spelling and stuff.

[JesseH]

.Paul.
The list box has tasks that the user will choose. Each task has a corresponding form associated with it. If the user selects the first item in the list box, say "Inventory By Class", I would like to open a form "InvByClass.vb". The name of the form is located in an array that matches the list box entries.
If there is another way for me to open the form "InvByClass.vb" that I will not know until selected by the user, I will be glad to use it.

Thanks for your help

[JesseH]

Nerd44, I tried the change you suggested an I got another system error. Thanks for trying.

[.paul.]

use custom list items

Public Class listItem
 
    Public display As String
    Public frm As Form
 
    Public Overrides Function ToString() As String
        Return Me.display
    End Function
 
    Public Sub New(ByVal display As String, ByVal form As Form)
        Me.display = display
        Me.frm = form
    End Sub
 
End Class

then to add to the list:

Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim li As New listItem("two", Form2)
        ListBox1.Items.Add(li)
        li = New listItem("three", Form3)
        ListBox1.Items.Add(li)
    End Sub
 
end class

to open the form when the list item is selected:

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
    DirectCast(ListBox1.SelectedItem, listItem).frm.Show()
End Sub

[.paul.]

to allow for opening + closing the forms more than once, you need to cancel the form from closing + hide it instead

Private Sub Form2_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
    e.Cancel = True
    Me.Hide()
End Sub

[Dr. Octagonapus]

Activator.CreateInstance(Type.GetType(WFormName)) <==== Error Here

You probably need to add your project's namespace to the front.

Activator.CreateInstance(Type.GetType("MyProject." & WFormName))

[Nerd44]

I dont know what u've done, on my system it works:

Public Class Form1
 
   Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
      Me.ListBox1.DisplayMember = "Name"
      For Each F In New Type() {GetType(Form2), GetType(Form3)}
         Me.ListBox1.Items.Add(F)
      Next
   End Sub
 
   Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs) Handles ListBox1.SelectedIndexChanged
      With DirectCast(sender, ListBox)
         If .SelectedIndex < 0 Then Return
         Dim O = Activator.CreateInstance(DirectCast(ListBox1.SelectedItem, Type))
         DirectCast(O, Form).Show()
      End With
   End Sub
 
End Class

but its not very useful for anything, i think.
On MDI-Variations i use a further developed kind of this technique to manage some mdi-Children.