Question

I have a mdicontainer form that summons forms. My problem is when the a user clicks again the menu for that form, it also make another instance of it.

What I did is declare a public class with a public variable on it ex: Boolean isFormOneOpen = false. Then every time formOne opens, it checks first the global variable I declared a while ago if it’s false, if it is, instantiate an object of a formOne and then show it. Otherwise, do nothing. Very static, imagine if I have many forms, I have to declare a variable for each form to check if it’s already open. Can you provide me a solution for this? Maybe a method that accepts a Form? Or any more clever way to do this.

Answer 1

You don’t need a variable, you could iterate the MdiChildren collection to see if the form is already opened. For example:

Private Sub btnViewChild_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnViewChild.Click
    For Each child In Me.MdiChildren
        If TypeOf child Is Form2 Then
            child.WindowState = FormWindowState.Normal
            child.Focus()
            Exit sub
        End If
    Next
    Dim frm As New Form2
    frm.MdiParent = Me
    frm.Show()
End Sub

The VB.NET-centric solution:

Private Sub btnViewChild_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnViewChild.Click
    Form2.MdiParent = Me
    Form2.WindowState = FormWindowState.Normal
    Form2.Show
End Sub