making OnPaint() fire

[WolfmanYoda]

I'm working through a book, "Professional C#" from Wrox publishing, and there is a part about displaying an image I'm working on.

Here is the OnPaint() code from the book, which works great, scrollbars and all:

protected override void OnPaint(PaintEventArgs e)
	{
		base.OnPaint(e);
		Graphics dc = e.Graphics;
		dc.ScaleTransform(scaleX, scaleY);
		dc.TranslateTransform(this.AutoScrollPosition.X, this.AutoScrollPosition.Y);
		dc.DrawImage(piccy, piccyBounds);
	}

Love it. Now I wanted to do more with it, so I added my own buttons to zoom in or out of the image.

I can get it to resize the image, but if I use the scrollbars it screws up the image. Here is my code:

        private void btnZoomOut_Click(object sender, System.EventArgs e)
	{
		scaleX = scaleX / 2;
		scaleY = scaleY / 2;
		((Control)sender).Parent.Refresh();
	}

private void btnZoomIn_Click(object sender, System.EventArgs e)
	{
		scaleX = scaleX * 2;
		scaleY = scaleY * 2;
		((Control)sender).Parent.Refresh();
	}

I figure if I add a line to each button_Click to make OnPaint() fire up, it will solve the scroll problem.

I've searched(in the book, MSDN, on the net, and here) to no avail on how to make OnPaint() fire. I found some info on Delegates, but I didn't understand the explanation on them.

So...can anyone tell me how to make OnPaint() fire?

[Arch4ngel]

this.OnPaint(null);

[WolfmanYoda]

Ahhh...thanks. I tried this.OnPaint() with all kinds of arguments except Null.

Man I feel dumb :)

[dynamic_sysop]

you can also use invalidate...

	private void button1_Click(object sender, System.EventArgs e)
	{
		this.Invalidate();
	}

[Arch4ngel]

yup ! and I think that this.Invalidate() is better than my dummy call...

Hummmmmm... to tell the truth I don't know which one is best.

 

On my part I prefer OnPaint(null). I'm sure it don't do nothing stupid :D

Hehe one way or another the job's done.

[WolfmanYoda]

I tried them both, I used

this.Invalidate();

 

for my zoom out button and

this.OnPaint(null);

 

for my zoom in button.

They both work great, I was just about to ask which one is better. Thanks guys :)

[divil]

You should not call OnPaint(null). If you do, how are you going to actually use the method to paint anything, since you have no PaintEventArgs and therefore no Graphics?