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VB.net PaintEventArgs Handling.

Posted on 2016-11-05
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Last Modified: 2016-11-09
I am working on a graphics intensive project and would like to create a class that includes a number of drawing routines. These routines could then be called from any number of places in the code. Here's an example of the type of function that I'd like to include in the class:

  Private Sub DrawEllipseGeom(
    ByVal numX As Integer,
    ByVal numY As Integer,
    ByVal numWidth As Integer,
    ByVal numHeight As Integer,
    ByVal colColor As Color,
    ByVal LineWidth As Long)

    Dim penDraw As New Pen(Drawing.Color.Black)
    Dim PenColor As Color = colColor
    penDraw.Color = PenColor
    penDraw.Width = LineWidth
 
    e.graphics.DrawEllipse(penDraw, numX, numY, numWidth, numHeight)
    Me.Invalidate()
    penDraw.Dispose()
  End Sub

The problem I'm trying to solve concerns passing e as PaintEventArgs to the functions in the class. Is there a way to do this or do I need to rethink my approach? I understand that the example above is trivial, but some of the functions will create multiple paths, perform transformations, etc. I would prefer not to have to recreate the code on each form by overriding the paint on each form.

Any ideas?

Thank you for reading my post.
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Question by:fritz_the_blank
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10 Comments
 
LVL 45

Expert Comment

by:AndyAinscow
ID: 41875945
>>The problem I'm trying to solve concerns passing e as PaintEventArgs to the functions in the class

Why is that a problem?
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LVL 46

Author Comment

by:fritz_the_blank
ID: 41876335
Thank you for answering. Let's say that I'd like to fire the code above from a button. The function expects e as PaintEventArgs as a parameter. I can't seem to pass that to the function via a click event.
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LVL 45

Expert Comment

by:AndyAinscow
ID: 41876383
Have a look at:
https://msdn.microsoft.com/en-us/library/5y289054(v=vs.110).aspx

I've not tried it but this might be what you want
   ' Create a Graphics object for the Control.
   Dim g As Graphics = Me.CreateGraphics()
   MyCustomDrawingRoutine(g)
  g.Dispose()
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LVL 46

Author Comment

by:fritz_the_blank
ID: 41876390
Thank you for your comment.

I'm able to do that, but there's a big difference between using .CreateGraphics and e. as PaintEventArgs. I need to be able to create paths and figures from a variety of functions and have them work with the same event handler. This allows me to create layers, manipulate them, stack them, and then finally output them in the order needed.
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LVL 45

Expert Comment

by:AndyAinscow
ID: 41876401
If you use Invalidate in the button click then a paint event will be fired.  You might have to then call your routines from the paint event after all.

However I don't understand your problem.  the PaintEventArgs contains the graphics object, the rectangle needing redrawing and nothing else for drawing.
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LVL 46

Author Comment

by:fritz_the_blank
ID: 41876407
I'm sorry. Let me provide some code...

I override the paint handler like this:

  Private Sub frmDrawTestPaint(ByVal sender As Object, ByVal e As PaintEventArgs) Handles MyBase.Paint
    Dim g As Graphics = e.Graphics
  End Sub

Now, what I'd like to do is to pass g to different subroutines or functions.
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LVL 45

Expert Comment

by:AndyAinscow
ID: 41876636
As mentioned in an earlier comment - you pass it like you would any other parameter a function requires

  Private Sub frmDrawTestPaint(ByVal sender As Object, ByVal e As PaintEventArgs) Handles MyBase.Paint
    Dim g As Graphics = e.Graphics
MyCustomDrawingRoutine(g)
  End Sub
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LVL 46

Author Comment

by:fritz_the_blank
ID: 41877536
Andy--

Thank you for staying with me! I've been away from programming for a while, and I haven't had time to study event handling in .Net as yet. So, let's say I call the routine from a form button:

  Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
     frmDrawTestPaint(Me, e)
  End Sub

I receive an error indicating that the mouse click event cannot be converted to a paint event. That makes sense, but I don't know how to get around that.
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Accepted Solution

by:
AndyAinscow earned 2000 total points
ID: 41877557
An Invalidate will flag for a repaint.  As you want to run a function after the button click then something like the following (air code) is along the lines of what you want.
private bRunFunction as boolean = false

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
     bRunFunction = true
     Invalidate
  End Sub

Sub Paint(.....)
  if bRunFunction then MyCustomDrawRoutine(e.Graphics)   'or e if you wanted other things in the PaintEventArgs
end sub
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LVL 46

Author Closing Comment

by:fritz_the_blank
ID: 41881178
Thank you very much. That's just what I needed.
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