Custom Control - OnPaint - not drawing

[Ashutosh]

Hi,
I am trying to create a custom control in which I have to display my custom
data. The custom control is placed on a form and docked completely. When I
have the following code for the custom control, it doesn't re-paint all the
data when I re-size the form vertically at run time. If I switch to other
window and use ALT-TAB to switch back to my form, everything works fine.


The code for my custom control is

public partial class CustomControl1 : Control
{
Dictionary<int, string> data = new Dictionary<int, string>();
public CustomControl1()
{
InitializeComponent();
for (int i = 1; i <= 40; i++)
{
data[i * 20] = "This is a sample text for line number " +
i.ToString();
}
}

protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
foreach (int y in data.Keys)
{
if (e.ClipRectangle.Y <= y && (e.ClipRectangle.Y +
e.ClipRectangle.Height) >= y)
{
e.Graphics.DrawString(data[y], SystemFonts.DefaultFont,
SystemBrushes.ControlText, new PointF(20, y));
}
}
}
}

I am actually confused with the the usage of ClipRectangle. Please advice.

Thanks & Regards,
Ashu

 

[Linda Liu[MSFT]]

Hi Ashu,

I performed a test on your sample code and did see the problem on my side.

If you print out the value of the PaintEventArgs.ClipRectangle property
from within the OnPaint method, you will see why the custom control doesn't
re-paint all the data when the form is resized vertically at tun time.

protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
// add this line of code to print the value of the
ClipRectangle property to the Output window
Console.WriteLine(e.ClipRectangle.ToString());
foreach (int y in data.Keys)
{
if (e.ClipRectangle.Y <= y && (e.ClipRectangle.Y +
e.ClipRectangle.Height) >= y)
{
e.Graphics.DrawString(data[y], SystemFonts.DefaultFont,
SystemBrushes.ControlText, new PointF(20, y));
}
}
}

Press F5 to run the application and resize the form vertically. The values
printed in the Output window are as follows:

{X=0,Y=0,Width=419,Height=413}
{X=0,Y=413,Width=419,Height=3}
{X=0,Y=416,Width=419,Height=3}
{X=0,Y=419,Width=419,Height=8}
{X=0,Y=427,Width=419,Height=3}
{X=0,Y=430,Width=419,Height=3}
{X=0,Y=433,Width=419,Height=1}
{X=0,Y=434,Width=419,Height=2}
{X=0,Y=436,Width=419,Height=4}
{X=0,Y=440,Width=419,Height=5}
{X=0,Y=445,Width=419,Height=3}
{X=0,Y=448,Width=419,Height=9}
{X=0,Y=457,Width=419,Height=2}
...

As you can see, the Paint event of the custom control is raised continously
when I resize the form. Each time when the Paint event is raised, the
PaintEventArgs.ClipRectangle is a small rectangle that doesn't meet the
condition you set in the OnPaint method. Thus, the new strings are not
drawn in the new rectangle on the custom control that needs painting.

Use the ClientRectangle property of the custom control instead of the
PaintEventArgs.ClipRectangle and this should solve your problem. For
example:

protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
foreach (int y in data.Keys)
{
if (this.ClientRectangle.Y <= y && (this.ClientRectangle.Y
+ this.ClientRectangle.Height) >= y)
{
e.Graphics.DrawString(data[y], SystemFonts.DefaultFont,
SystemBrushes.ControlText, new PointF(20, y));
}
}
}

Hope this helps.
If you have anything unclear, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

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[Ashutosh]

Hi,
Please ignore the post! The issue is resolved.

I didn't consider the various cases of overlapping of clipping region and he
drawing text.

Thanks & Regards,
Ashu