C# Invalidate troubles | 易学教程

问题

I am trying to move a drawn graphics item, I can draw them just fine. but when I try to move it, it just draws another item over the original. I have tried Invalidate, and pictureBox1.Invalidate. still no luck just prints both items to the pictureBox. Thanks for any suggestions.

     private void button1_Click(object sender, EventArgs e)
    {
        count++;
        button1.Text = "Move";

        if (count == 1)
        {

         car();
        }
        else if (count == 2)
        {

            car1();
        }
    }
    public void car()
    {
        Invalidate();
        g = pictureBox1.CreateGraphics();
        g.DrawEllipse(pen1, 50, 125, 30, 30);
        g.DrawEllipse(pen1, 150, 125, 30, 30);
        g.DrawRectangle(pen2, 45, 75, 140, 50);
        g.DrawLine(pen2, 65, 75, 80, 35);
        g.DrawLine(pen2, 80, 35, 140, 35);
        g.DrawLine(pen2, 140, 35, 160, 75);
        // Create string to draw.
        String drawString = "Price: "+(cost).ToString("C");
        // Create font and brush.
        Font drawFont = new Font("Arial", 16);
        SolidBrush drawBrush = new SolidBrush(Color.Black);
        // Create point for upper-left corner of drawing.
        PointF drawPoint = new PointF(50, 95);
        // Draw string to screen.
        g.DrawString(drawString, drawFont, drawBrush, drawPoint);

    }
    public void car1()
    {
        Invalidate(); 
        g = pictureBox1.CreateGraphics();
        g.DrawEllipse(pen1, 50 + m, 125, 30 , 30 );
        g.DrawEllipse(pen1, 150 + m, 125, 30 , 30);
        g.DrawRectangle(pen2, 45 + m, 75, 140, 50 );
        g.DrawLine(pen2, 65 + m, 75, 80 + m, 35);
        g.DrawLine(pen2, 80 + m, 35, 140 + m, 35);
        g.DrawLine(pen2, 140 + m, 35, 160 + m, 75);
        // Create string to draw.
        String drawString = "Price: " + (cost).ToString("C");
        // Create font and brush.
        Font drawFont = new Font("Arial", 16);
        SolidBrush drawBrush = new SolidBrush(Color.Black);
        // Create point for upper-left corner of drawing.
        PointF drawPoint = new PointF(50 + m, 95);
        // Draw string to screen.
        g.DrawString(drawString, drawFont, drawBrush, drawPoint);
    }

回答1:

Move your code to the Paint event of the picturebox and use the graphics object from the available arguments.

private void pictureBox1_Paint(object sender, PaintEventArgs e) {
  e.Graphics.Clear(Color.White);

  if (count == 1)
    DrawCar1(e.Graphics);

  if (count == 2)
    DrawCar2(e.Graphics);
}

public void DrawCar1(Graphics g)
{
  g.DrawEllipse(pen1, 50, 125, 30, 30);
  g.DrawEllipse(pen1, 150, 125, 30, 30);
  // etc.
}

public void DrawCar2(Graphics g)
{
  // etc.
}

private void button1_Click(object sender, EventArgs e)
{
  count++;
  button1.Text = "Move";
  pictureBox.Invalidate();
}

Your code never cleared the PictureBox, just the form, but it's a mistake to use CreateGraphics() because that is just a temporary canvas. Any drawing using that method gets wiped out when you minimize the form, for instance.

Your code should probably be refactored into having a "Car" class. Having a Car1 and a Car2 drawing routine isn't very practical. If you want to keep moving it, you don't want to keep adding more Car# routines. Create a single drawing routine for the car and keep the location information in the "Car" class so you know "where" you want the car drawn.

来源：https://stackoverflow.com/questions/9521507/c-sharp-invalidate-troubles

标签

invalidation