using g.DrawRectangle(pen,rect) to draw a rectangle on an object

[Colin McGuire]

Hi there. I have written a small procedure to draw various shapes on
things. A bit of it is shown below.

Private Sub drawShape(ByVal shapeType As Integer, ByRef g As Graphics)
Select Case shapeType
Case 1 : g.DrawRectangle(New Pen(Color.Black), 0, 0, 50, 10)
Case 2 'draw a circle
Case 3 'draw a triangle
Case 4 'draw other shape
Case 5 'draw other shape
Case 6 'draw other shape
Case Else 'etc. draw other shapes
End Select
End Sub

If on Form1, I override the OnPaint method with

Protected Overrides Sub OnPaint(ByVal e As
System.Windows.Forms.PaintEventArgs)
MyBase.OnPaint(e)
drawShape(1, e.Graphics)
End Sub

it paints my rectangle as I would expect drawing it on Form1 at 0,0
with width 50 and height 10.

I have lots of other controls on the form, such as buttons, labels,
groupboxes etc. My question is how do I get 'g' (a valid Graphics
instance) for the buttons, labels, groupboxes and other things.

The obvious thing I tried below doesn't work (I see no rectangle on
the GroupBox, called GroupBox1) but still see the rectangle on the
form. I want to see both.

Protected Overrides Sub OnPaint(ByVal e As
System.Windows.Forms.PaintEventArgs)
MyBase.OnPaint(e)
drawShape(1, e.Graphics)
drawShape(1, Me.GroupBox1.Creategraphics())
End Sub


Thank you in advance for all your help and sorry to post more of these
verbose and tricky questions.
Colin

 

[Hexathioorthooxalate]

Colin - you have come a long way judging by the type of questions you are
now asking.

I'm not going to answer your question directly but provide you with some
information that should enable you to work out the answer to your question
yourself.

If Panel1 is a Panel on your form, TabControl1 is a TabControl on your form,
and Button1 is a Button on your form, when OnPaint is executed

Protected Overrides Sub OnPaint(ByVal e As
System.Windows.Forms.PaintEventArgs)
MyBase.OnPaint(e)
Dim g As Graphics = Panel1.CreateGraphics()
drawShape(1, g)
g.Dispose()
g=TabControl1.CreateGraphics()
drawShape(1,g)
g.Dispose()
g=Button1.Creategraphics()
drawShape(1,g)
g.Dispose()
End Sub

you will see your blue rectangle on both Panel1 and TabControl1, but not
Button1. Ask yourself why the rectangle draws on some form objects but not
others - what is different about them and how would/could you change the
observed behaviour.

Regards
Hexathioorthooxalate


PS: Here's an excerpt from the on-line (VB.NET 2003) docs for
CreateGraphics. Quote: "The returned Graphics object must be disposed
through a call to its Dispose method when it is no longer needed.". Your use
of drawShape(1, Me.GroupBox1.Creategraphics()) doesn't and can't dispose of
the graphics object as written.

 

[Colin McGuire]

Hex - thanks for your help.

The Panel etc are .Net controls, and the Button is a Windows control?
But I still want to draw on the Button too. How?
Thank you
Colin.

 

[Colin McGuire]

Hex isnt online today. Could someone else help me out here please.

I can see that rectangles are only drawn on objects that are not
Windows controls (such as buttons and textboxes).

How can I tell as a general rule whether the object is drawn by the
framework and not by Windows? Currently a "GroupBox" is drawn by the
framework but what if Microsoft modify Windows so that it is drawn
there - then my code won't work. So what I think I want it a
subroutine to pass a object (like a button, or a panel, or a
groupbox), and the subroutine print out whether the object is drawn by
Windows or the framework (and therefore whether my blue rectangle,
code below, will be drawn).
Thank you
Colin