Drawing a triangle in a picture box

Hi there

I am trying to draw a triangle in a picture box.  I don't seem to get an error but nothing is displaying in the picture box.  Does anyone know what I am doing wrong?  I have tried pic.refresh and that doesn't seem to do anything
     
  Dim poly(3) As PointF ', NumCoords As Long, hBrush As Long, hRgn As Long

                poly(1).X = 0
                poly(1).Y = 0
                poly(2).X = 0
                poly(2).Y = pic.Height
                poly(3).X = pic.Width
                poly(3).Y = pic.Height

            'Get PictureBox's Graphics Object
            Dim gr As Graphics = pic.CreateGraphics
            Dim pn As Pen = Pens.AliceBlue
            gr.DrawPolygon(pn, poly)
            pic.Refresh()
            gr.Dispose()

Thanks for your help in advance
DavidGreenfieldAsked:
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dctuckCommented:
It's because the image gets repainted with its default contents whenever a refresh occurs.

If you put the code inside the Paint event for your pic it should work. e.g:

Private Sub pic_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles pic.Paint
     Dim poly(3) As PointF ', NumCoords As Long, hBrush As Long, hRgn As Long
    poly(1).X = 0
    poly(1).Y = 0
    poly(2).X = 0
    poly(2).Y = pic.Height
    poly(3).X = pic.Width
    poly(3).Y = pic.Height
    'Get PictureBox's Graphics Object
    Dim gr As Graphics = pic.CreateGraphics
    Dim pn As Pen = Pens.AliceBlue
    gr.DrawPolygon(pn, poly)
    pic.Refresh()
    gr.Dispose()
End Sub
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Lol dctuck...it isn't really any better to place the code into the Paint() event when you left the call to CreateGraphics() in there...

...also, the call to pic.Refresh() in the Paint() event will lead to an infinite refreshing loop and alot of flicker...

DavidGreenfield...Arrays start at index 0 (zero) in .Net.

(On a side note...with the default picturebox background color, Pens.AliceBlue was barely visible on my system so I switched to Pens.Black)

Use the graphics supplied in the "e" parameter of the Paint() event.  If you move the Point Array to the form level then you can update the points dynamically and cause the triangle to change.

For example:

Public Class Form1

    Private poly() As Point

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        poly = New Point() { _
            New Point(0, 0), _
            New Point(0, pic.Height - 1), _
            New Point(pic.Width - 1, pic.Height - 1)}
    End Sub

    Private Sub pic_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles pic.Paint
        e.Graphics.DrawPolygon(Pens.Black, poly)
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        poly(0).X = 25
        poly(2) = New Point(pic.Width / 2, pic.Height / 2)
        pic.Refresh()
    End Sub

End Class
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dctuckCommented:
Idle_Mind - I know, I forgot to adjust that: I checked the code in VB and then went and copy and pasted the original code without changing it.... d'oh!
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Hehe...I can't say I've never done a similar thing.   =)
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