Stay inside MDI Client Area

Michael Russell

In MDI applications, it is a common occurance for the user to open several different forms. However, even if one form is closed, the "offset" used to place the subsequent forms is remembered, so each form is gradually shifted down and to the right until it shifts partially or fully outside of the MDI client area. I'd like to ensure that the MDI clients are always completely within the MDI client area upon first being opened. I have come up with a hack involving the OnVisibleChanged event and two helper functions (listed below), but is there a more graceful way of doing this?

' In each form
    Protected Overrides Sub OnVisibleChanged(ByVal e As System.EventArgs)
        EnsureInsideMDIArea(Me)
    End Sub

' Helper functions in a module
    Public Function GetMDIClientRect(ByVal frm As Form) As Rectangle
        Dim pr As Rectangle = Rectangle.Empty
        For Each c As Control In frm.Controls
            If TypeOf c Is MdiClient Then pr = c.ClientRectangle
        Next
        Return pr
    End Function

    Public Sub EnsureInsideMDIArea(ByVal frm As Form)
        ' Ignore if not an MDI client
        If Not (frm.MdiParent Is Nothing) Then

            ' Get parent rect
            Dim pr As Rectangle = GetMDIClientRect(frm.MdiParent)

            Dim r, b As Integer
            r = frm.Size.Width + frm.Left
            b = frm.Size.Height + frm.Top

            If r > pr.Right Or b > pr.Bottom Then
                frm.Top = 0
                frm.Left = 0
            End If

        End If
    End Sub

Dave Kreskowiak

Graceful is in the eye of the beholder. If what you wrote works for you, great! Another method, though, would be to put this kind of code entirely in the MDI Parent and when you create the new child form, you can get it's size and make sure that it is inside the MDI Parent's client window without iterating through all the controls...

' In MDI Parent

Private Sub MenuItem2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MenuItem2.Click
Dim newChild As New frmChild
newChild.MdiParent = Me

    ' You must show the form before it will receive its Top and Left values.  If you send
    ' the new form to EnsureChildInClientArea first, its Top and Left will always be 0,0.
    newChild.Show()
    EnsureChildInClientArea(newChild)
End Sub

Private Sub EnsureChildInClientArea(ByRef frmChild As Form)
Dim r, b As Integer
r = frmChild.Width + frmChild.Left
b = frmChild.Height + frmChild.Top
If r > Me.ClientSize.Width Or b > Me.ClientSize.Height Then
frmChild.Top = 0
frmChild.Left = 0
End If
End Sub

RageInTheMachine9532

Michael Russell

That would almost work. We'd need an Application.DoEvents after the newChild.Show because the top/left are not set until the new form is actually visible (very frustrating trying to figure THAT out...), and we'd actually need to check the MdiClient size, not just the ClientSize, or else status bars and what not would not be taken into account. The biggest problem I have with the current solution is that when the form is created, it shows at the original location for 1/60th of a second, and the flicker looks bad.

Dave Kreskowiak

It was quick and dirty, but it worked. No intensive testing on it though... It was just an idea! :) RageInTheMachine9532