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OnPaint Not Getting Called on Invalidate()

I'm trying to create "rubber-band" rectangles by overriding the
OnPaint method to place rectangles on top of all graphic controls, but
when I call Me.Invalidate() (when the user moves the mouse), OnPaint
is not getting called... Here is the relevent code:

I'm trying to create a "rubber band" rectangle effect on my form.

Private Sub HighlightSectio nOfTrack(ByVal sender As Object, ByVal e
As
System.Windows. Forms.MouseEven tArgs) Handles GraphicsPB.Mous eMove

If LeftMouseButton Down Then
DragEndPoint = New Point(e.X, e.Y)
Me.Invalidate()
End If
End Sub
Protected Overrides Sub OnPaint(ByVal e As
System.Windows. Forms.PaintEven tArgs) MyBase.OnPaint( e)

If Math.Abs(DragSt artPoint.X - DragEndPoint.X) 1 And
Math.Abs(DragSt artPoint.Y - DragEndPoint.Y) 1 And
LeftMouseButton Down Then
Dim XLoc As Integer = Math.Min(DragSt artPoint.X +
GraphicsPB.Loca tion.X, DragEndPoint.X + GraphicsPB.Loca tion.X)
Dim YLoc As Integer = Math.Min(DragSt artPoint.Y +
GraphicsPB.Loca tion.Y, DragEndPoint.Y + GraphicsPB.Loca tion.Y)
e.Graphics.Draw Rectangle(Pens. Red, XLoc, YLoc,
CInt(Math.Abs(D ragStartPoint.X - DragEndPoint.X) ),
CInt(Math.Abs(D ragStartPoint.Y - DragEndPoint.Y) ))
End If
End Sub
The OnPaint method is not getting called when Me.Invalidate is
called!!!! I tried calling Me.Refresh() to no avail also. I know this
because I put an if statement inside the OnPaint method and put a
breakpoint there... What gives??

Jun 20 '07 #1
1 3610

There should not be any problems.

My guess is that you are handling MouseMove events for a
PictureBox (GraphicsPB) child control but invalidating the form
(Me.Invalidate) instead of the picturebox control
(GraphicsPB.Inv alidate)? Invalidating the form does not invalidate
the child controls. Start a new project, add a picturebox to a form,
then run the code below: Only the form receives paint events
when the form is invalidated by the timer. The picturebox is only
invalidated if you move something else over it and exposes it again.

One other thing: Your Abs(startpos-endpos) condition is written
in such a way that a rectangle won't appear until it has a size of
at least 3x3 pixels. Sure this is what you want rather than perhaps
2x2 pixels or even 1x2 or 2x1 pixels?

Regards,

Joergen Bech

---snip---

Public Class Form1
Private WithEvents invalidateTimer As Timer

Protected Overrides Sub OnPaint(ByVal e As
System.Windows. Forms.PaintEven tArgs)
MyBase.OnPaint( e)
Debug.WriteLine ("OnPaint")
End Sub

Private Sub Form1_Load(ByVa l sender As Object, ByVal e As
System.EventArg s) Handles Me.Load
invalidateTimer = New Timer
With invalidateTimer
.Interval = 500
.Enabled = True
End With
End Sub

Private Sub invalidateTimer _Tick(ByVal sender As Object, ByVal e
As System.EventArg s) Handles invalidateTimer .Tick
Me.Invalidate()
End Sub

Private Sub PictureBox1_Pai nt(ByVal sender As Object, ByVal e As
System.Windows. Forms.PaintEven tArgs) Handles PictureBox1.Pai nt
Debug.WriteLine ("PictureBox1_P aint")
End Sub

End Class

---snip---

On Wed, 20 Jun 2007 08:12:03 -0700, "se**@rlc.c om" <se**@rlc.com >
wrote:
>I'm trying to create "rubber-band" rectangles by overriding the
OnPaint method to place rectangles on top of all graphic controls, but
when I call Me.Invalidate() (when the user moves the mouse), OnPaint
is not getting called... Here is the relevent code:

I'm trying to create a "rubber band" rectangle effect on my form.

Private Sub HighlightSectio nOfTrack(ByVal sender As Object, ByVal e
As
System.Windows .Forms.MouseEve ntArgs) Handles GraphicsPB.Mous eMove

If LeftMouseButton Down Then
DragEndPoint = New Point(e.X, e.Y)
Me.Invalidate()
End If
End Sub
Protected Overrides Sub OnPaint(ByVal e As
System.Windows .Forms.PaintEve ntArgs) MyBase.OnPaint( e)

If Math.Abs(DragSt artPoint.X - DragEndPoint.X) 1 And
Math.Abs(DragSt artPoint.Y - DragEndPoint.Y) 1 And
LeftMouseButton Down Then
Dim XLoc As Integer = Math.Min(DragSt artPoint.X +
GraphicsPB.Loc ation.X, DragEndPoint.X + GraphicsPB.Loca tion.X)
Dim YLoc As Integer = Math.Min(DragSt artPoint.Y +
GraphicsPB.Loc ation.Y, DragEndPoint.Y + GraphicsPB.Loca tion.Y)
e.Graphics.Draw Rectangle(Pens. Red, XLoc, YLoc,
CInt(Math.Abs(D ragStartPoint.X - DragEndPoint.X) ),
CInt(Math.Abs(D ragStartPoint.Y - DragEndPoint.Y) ))
End If
End Sub
The OnPaint method is not getting called when Me.Invalidate is
called!!!! I tried calling Me.Refresh() to no avail also. I know this
because I put an if statement inside the OnPaint method and put a
breakpoint there... What gives??
Jun 20 '07 #2

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