GDI

  • Thread starter Thread starter TyBreaker
  • Start date Start date
T

TyBreaker

Hi, I have the routine below where I wish to render a pie chart on a
button. The routine works if I use the commented out code but I
recently discovered a shorter way to do it (just the single line at the
bottom of the routine). Only problem is the pie chart doesn't appear at
all when I try the short method. I don't get any errors, it just
doesn't appear. Any thoughts?

Private Sub piechart()
'Dim dg As Graphics
Dim sb = New SolidBrush(Color.Blue)

'me.button1.Image = New Bitmap(me.button1.Width, me.button1.Height)
'dg = Graphics.FromImage(me.button1.Image)
'dg.FillPie(sb, 0, 0, 50, 50, 0, 90)
me.button1.CreateGraphics.FillPie(sb, 0, 0, 50, 50, 0, 90)
End Sub
--
______ ___ __
/_ __/_ __/ _ )_______ ___ _/ /_____ ____
/ / / // / _ / __/ -_) _ `/ '_/ -_) __/
/_/ \_, /____/_/ \__/\_,_/_/\_\\__/_/
/___/

There are 10 types of people in this world; those who understand the
binary numbering system and those who don't.

There's no place like 127.0.0.1.

ASCII a silly question, get a silly ANSI.
 
Hi TyBreaker, actually it works but you can't see it because it is
immediately painted over. The other way you used, instead, creates a
*persistent* drawing. When a Graphic object is not created from a
bitmap it is not persistent.

You can do that way but have to work with on paint. Let me know if you
need more help...

-tom

TyBreaker ha scritto:
 
In the commented out code, you are drawing to the button's image. In the
uncommented code you are drawing directly to the button's graphics surface.
I'd guess that the button's normal paint cycle overwrites your drawing on
the graphics surface because the button doesn't know about your extra
drawing. The button is aware of its image, which is why the image drawing is
retained.

It should work if you handle the button's Paint event and call your method
in the Paint event handler. The PaintEventArgs passed with the Paint event
also provides a graphics surface for drawing on.

One final point is that you should remember to dispose of your brush and
your graphics surface by calling the Dispose method in a Finally block or by
using a Using..End Using statement. Don't dispose of the graphics surface if
it was provided by PaintEventArgs.
 
Kevin said:
It should work if you handle the button's Paint event and call your method
in the Paint event handler. The PaintEventArgs passed with the Paint event
also provides a graphics surface for drawing on.
Click to expand...

Thanks Kevin, I have since gone in a completely different direction -
much as you have described actually. I came across a GDI FAQ which
showed me I was doing things in the wrong way. I think I was breaking
every rule listed! I've since solved this problem by understanding
events better.
One final point is that you should remember to dispose of your brush and
your graphics surface by calling the Dispose method in a Finally block or by
using a Using..End Using statement. Don't dispose of the graphics surface if
it was provided by PaintEventArgs.
Click to expand...

OK, this is something new - I'm not quite understanding when I should
dispose of stuff yet. I basically dispose of nothing at the moment
because I never know when to. I essentially let it all dispose
naturally when the whole thing shuts down.

--
______ ___ __
/_ __/_ __/ _ )_______ ___ _/ /_____ ____
/ / / // / _ / __/ -_) _ `/ '_/ -_) __/
/_/ \_, /____/_/ \__/\_,_/_/\_\\__/_/
/___/

There are 10 types of people in this world; those who understand the
binary numbering system and those who don't.

There's no place like 127.0.0.1.

ASCII a silly question, get a silly ANSI.
 
Glad to here you've got it working.

With regards to Dispose, a simple rule to follow is if you created an
instance of a disposable object, call Dispose when you're done with it. If
the object was provided for you, as in the Paint event case, don't call
Dispose. This isn't an absolute rule, for example you have to be careful
when adding disposable objects to collections because some collections will
store a reference and others will store a copy, but it should help you get
started.
 
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