Animated closing for windows form

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VB

WinForms

Hello,
I'm trying put some animation effects in my windows form application. here is my code:-

Private Const AW_BLEND = &H80000  'Uses a fade effect. This flag can be used only if hwnd is a top-level window.
   Private Declare Function AnimateWindow Lib "user32" (ByVal hwnd As Int32, ByVal dwTime As Int32, ByVal dwFlags As Int32) As Boolean
   Dim winHide As Integer = &H10000
   Dim winBlend As Integer = &H80000

and in the formclosing event:-

Private Sub add_branch_FormClosing(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles MyBase.FormClosing
       AnimateWindow(Me.Handle.ToInt32, CInt(1200), winHide Or winBlend)
       e.Cancel = False
   End Sub

This's not working , if I'm making this form as a child of my MDI form,i.e.

Private Sub AddBranchToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AddBranchToolStripMenuItem.Click

       add_branch.Show()
       add_branch.MdiParent = Me
   End Sub

It works without making it a child for the MDI,but How can I implement the animation with making the form as a child becoz if's not a child, then i'm loosing the form by clicking outside. I can't use showDialog().

Thankx for help....