How to delete a drawn circle in c# windows form?

问题

I have drawn a circle in windows form

Pen pen = new Pen(Color.Black, 3);
Graphics gr = this.CreateGraphics();
gr.DrawEllipse(pen, 5,5,20,20);

How to delete it...

回答1:

You can invalidate the draw region you want to refresh for example:

 this.Invalidate();

on the form...

回答2:

You have to clear your Graphic:

Graphics.Clear();

But all drawn figures will be cleared. Simply, you will then need to redraw all figures except that circle.

Also, you can use the Invalidate method:

Control.Invalidate()

It indicates a region to be redrawn inside your Graphics. But if you have intersecting figures you will have to redraw the figures you want visible inside the region except the circle.

This can become messy, you may want to check out how to design a control graph or use any graph layout library.

回答3:

Assuming you're subscribing to the Paint event or overriding the protected OnPaint routine, then you will need to perform something like this:

bool paint = false;

protected override void OnPaint(object sender, PaintEventArgs e)
{
  if (paint) 
  {
   // Draw circle.
  }
}

Then when you want to stop painting a circle:

paint = false;
this.Invalidate(); // Forces a redraw

回答4:

You don't "delete" it per se, there's nothing to delete. It's a drawing, you draw something else over it or you can call the Graphics.Clear() method.

回答5:

You can make a figure of same dimensions using the backColor of your control in which you are drawing

use after your code to clear your figure.

Pen p = new Pen(this.BackColor);   
gr.DrawEllipse(p, 5,5,20,20);

回答6:

If u are using Invalidate() and is not working, make a panel.Refresh().

That will work on you.

回答7:

In fact, you can delete your circle and nothing but your circle.

Everything you need is something like a screenshot of the "before state" of the area you want to clear, to make a TextureBrush from it. You can achieve that step by something like this:

Bitmap _Background = new Bitmap(this.Width, this.Height);
Graphics.FromImage(_Background).CopyFromScreen(this.Left, this.Top, 0, 0, this.Size);

The first line will give you a bitmap in your windows forms size. The second line will save a screenshot of it in the _Background-bitmap.

Now you create a TextureBrush out of it:

Brush brsBackground = new TextureBrush(_Background);

The next thing you need are the dimensions of your circle, so you should save them into a variable, if they are not a fix value. When you got them at hand, you can clear the specific area like this:

Graphics gr = this.CreateGraphics();
gr.FillEllipse(brsBackground, 5, 5, 20, 20); // values referred to your example

Done!

Even complex figures are able to be deleted by this, like a GraphicsPath for example:

GraphicsPath gp = new GraphicsPath(); // any kind of GraphicsPath
gr.FillRegion(brsBackground, new Region(gp));

回答8:

It is very simple to delete a drawn circle from c.

There is only four steps:-

Open turbo app
go to the command where you had drawn the circle
drag the command
click on delete button

来源：https://stackoverflow.com/questions/4124638/how-to-delete-a-drawn-circle-in-c-sharp-windows-form

标签

graphics