Visual Basic > Forms

How to center a form on a parent window.

How to center a form on a parent window.

'Note: This has only been tested with VB 3 and VB 4-16, if you convert



' This procedure centers a Form over a Parent window.
' This dialog-centering algorithm works well when you're
' not sure of the resolution of the target computer.

' Declare this Type in a .Bas module:

Type RECT
   Left As Integer
   Top As Integer
   Right As Integer
   Bottom As Integer
End Type

' Declare this API
 Declare Sub GetWindowRect Lib "User" (ByVal hWnd%, lpRect As RECT)

' Add the DialogCenterParent rountine:

Sub DialogCenterParent (ByVal hWndParent As Integer, frmDialog As Form)
Dim iLeft As Integer
Dim iTop As Integer
Dim iMidX As Integer
Dim iMidY As Integer
Dim rcParent As RECT

' Find the ideal center point.
If hWndParent = 0 Then
   'No parent, so center over the enter screen
   iMidX = Screen.Width / 2
   iMidY = Screen.Height / 2
Else

'Center over the form's parent.

Call GetWindowRect(hWndParent, rcParent)
     ' Next 2 lines as one single line.
     iMidX = ((rcParent.Left * Screen.TwipsPerPixelX) + 
              (rcParent.Right * Screen.TwipsPerPixelY)) / 2
     ' Next 2 lines as one single line.
     iMidY = ((rcParent.Top * Screen.TwipsPerPixelY) + 
              (rcParent.Bottom * Screen.TwipsPerPixelY)) / 2
End If

' Find the form's upper left based on that

iLeft = iMidX - (frmDialog.Width / 2)
iTop = iMidY - (frmDialog.Height / 2)

' If the form is outside the screen, move it inside

If iLeft < 0 Then
   iLeft = 0
   ElseIf (iLeft + frmDialog.Width) > Screen.Width Then
   iLeft = Screen.Width - frmDialog.Width
End If

If iTop < 0 Then
   iTop = 0
   ElseIf (iTop + frmDialog.Height) > Screen.Height Then
   iTop = Screen.Height - frmDialog.Height
End If

' Move the form to it's new position
frmDialog.Move iLeft, iTop

End Sub

' Call the routine in the Form_Load event of the form to center:

' Substitute your Parent for Form1
  Call DialogCenterParent(Form1.hWnd, Me)