restricting multiple instances of child form?

I am using an MDI form with menu items.

I am using the following code to open a form when appropriate menu item is chosen. But I want to make sure if the user clicks on the same menu item multiple times, only one instance of the MDI child should be shown rather than mulitiple instance of the same (MDI child) form.

Dim NewMDIChild As New frmRateType
NewMDIChild.MdiParent = Me
NewMDIChild.StartPosition = FormStartPosition.CenterScreen
NewMDIChild.Show()

How can I restrict?

thanks
nath

Have a shared variable that determines if the form has already been instantiated (maybe a boolean or an integer if you want more than 1 but less than x instances).

In the constructor of the childform, query this variable and throw an exception if you already have enough instances.

Catch the exception in the calling sub.

is there any alternate way to do this?

Hi,

I have not yet tested this but see if the following helps:

In the Parent form load event
Public NewMDIChild as Form

Then in the Menu

NewMDIChild=Nothing
NewMDIChild = New frmRateType
NewMDIChild.MdiParent = Me
NewMDIChild.StartPosition = FormStartPosition.CenterScreen
NewMDIChild.Show()

thanks though.

nath

Hi,

Sorry, I should have said put the following in the General section of the Parent form:

Public NewMDIChild as Form

i agree with wossname. with that method, you can allow as many as you like if you ever feel the need later.

What about wossname's method isn't suitable for your program? It's the first thing I could think of when reading your question.

Try this:

VB Code:

Dim f As frmRateType
Dim fTest As Form
 
For Each fTest In MDIForm.MdiChildren
    If TypeOf fTest Is frmRateType Then
        f = DirectCast(fTest, frmRateType)
        'f now holds a reference to the first instance of 
        'frmRateType found in the MdiChildren collection
        Exit For
    End If
Next
 
If f Is Nothing Then
    f = New frmRateType()
    f.MdiParent = MDIForm
End If
 
f.Show()
f.Activate()