绘图应用双Graphics上下文下橡皮擦功能异常问题求助

代码中有两个Graphics对象：graphics负责创建图形，g用于通过方向键移动图形。原本通过白色画笔实现的擦除功能运行正常，但引入用于移动图形的g对象后，无法在移动后的图形所在上下文上完成擦除（图形创建后会立即绘制到g上下文）。目前临时方案是在MouseMove事件中通过CreateGraphics绘制白色线条，但点击窗体或选择绘图形状时，擦除的痕迹会消失。

以下是核心代码片段：

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
    startPoint = e.Location;
    draw = true;

    if (addtext)
    {
        TextBox textBox = new TextBox
        {
            Location = pictureBox1.PointToClient(MousePosition),
            Size = new Size(100, 20),
            ForeColor = Color.Black
        };

        textBox.Leave += (s, ev) =>
        {
            TextBox currentTextBox = (TextBox)s;
        };

        pictureBox1.Controls.Add(textBox);
        textBox.Focus();
        addtext = false;
    }

}


private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{

    if (draw)
    {
        if (choice == 1)
        {
            width = e.Location.X - startPoint.X;
            height = e.Location.Y - startPoint.Y;
            Rectangle shape = new Rectangle(startPoint.X, startPoint.Y, width, height);
            graphics.DrawRectangle(pen, shape);
            graphics.DrawRectangle(eraser, shape);
            pictureBox1.Refresh();
            draw = false;
        }
        else if (choice == 2)
        {
            width = e.Location.X - startPoint.X;
            height = e.Location.Y - startPoint.Y;
            Rectangle shape = new Rectangle(startPoint.X, startPoint.Y, width, height);
            graphics.DrawEllipse(pen, shape);
            graphics.DrawEllipse(eraser, shape);
            pictureBox1.Refresh();
            draw = false;
        }
        if (draw && choice == 3)
        {
            createPolygon(graphics, pen, startPoint, e.Location, 6);
            createPolygon(graphics, eraser, startPoint, e.Location, 6);
            draw = false;
        }
        else if (choice == 4)
        {
            createPolygon(graphics, pen, startPoint, e.Location, 4);
            createPolygon(graphics, eraser, startPoint, e.Location, 4);
            draw = false;
        }
        else if (choice == 5)
        {
            endPoint = e.Location;
            graphics.DrawLine(pen, startPoint, endPoint);
            graphics.DrawLine(eraser, startPoint, endPoint);
            draw = false;
        }
        else if (choice == 6)
        {
            graphics.DrawRectangle(pen, startPoint.X, startPoint.Y, Math.Abs(e.X - startPoint.X), Math.Abs(e.X - startPoint.X));
            graphics.DrawRectangle(eraser, startPoint.X, startPoint.Y, Math.Abs(e.X - startPoint.X), Math.Abs(e.X - startPoint.X));
            draw = false;
        }
        else if (choice == 7)
        {
            graphics.DrawEllipse(pen, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
            graphics.DrawEllipse(eraser, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
            draw = false;

        }
        else if (choice == 8)
        {
            Point[] point = { new Point(startPoint.X, startPoint.Y), new Point(startPoint.X, e.Y), new Point(startPoint.X, e.Y) };
            graphics.DrawPolygon(pen, point);
            Point[] point2 = { new Point(startPoint.X, startPoint.Y), new Point(startPoint.X, endPoint.Y), new Point(endPoint.X, endPoint.Y) };
            graphics.DrawPolygon(eraser, point2);
            draw = false;
        }
        else if (choice == 9)
        {
            Point[] point = { new Point(startPoint.X, startPoint.Y), new Point((startPoint.X + e.X) / 2, e.Y), new Point(e.X, startPoint.Y) };
            graphics.DrawPolygon(pen, point);
            graphics.DrawPolygon(eraser, point);
            draw = false;
        }
        else if (choice == 10)
        {
            graphics.DrawEllipse(pen, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
            graphics.DrawEllipse(pen, startPoint.X - 20, startPoint.Y - 20, (e.X - startPoint.X) + 40, (e.X - startPoint.X) + 40);
            graphics.DrawEllipse(eraser, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
            graphics.DrawEllipse(eraser, startPoint.X - 20, startPoint.Y - 20, (e.X - startPoint.X) + 40, (e.X - startPoint.X) + 40);
            draw = false;;
        }
        Shape newShape = new Shape
        {
            Type = choice,
            StartPoint = startPoint,
            EndPoint = endPoint,
            PenColor = pen.Color
        };
        shapes.Add(newShape);

        pictureBox1.Refresh();
    }
}
private void eraserToolStripMenuItem_Click(object sender, EventArgs e)//This is the box that is used for the erasing part
{
    eraserMode = !eraserMode;
    draw = true;
}

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
    if (eraserMode) //Here is the code for the Erasor
    {
        using (Graphics g = pictureBox1.CreateGraphics())
        {
            g.DrawLine(new Pen(Color.White, 6), startPoint, e.Location);
            startPoint = e.Location;

        }
    }
    if (draw && choice == 1)
    {
        width = e.Location.X - startPoint.X;
        height = e.Location.Y - startPoint.Y;
        graphics.DrawRectangle(eraser, startPoint.X, startPoint.Y, endPoint.X - startPoint.X, endPoint.Y - startPoint.Y);
        graphics.DrawRectangle(pen, startPoint.X, startPoint.Y, width, height);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }


    else if (draw && choice == 2)
    {
        width = e.Location.X - startPoint.X;
        height = e.Location.Y - startPoint.Y;
        graphics.DrawEllipse(eraser, startPoint.X, startPoint.Y, endPoint.X - startPoint.X, endPoint.Y - startPoint.Y);
        graphics.DrawEllipse(pen, startPoint.X, startPoint.Y, width, height);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }

    else if (draw && choice == 3)
    {
        createPolygon(graphics, eraser, startPoint, endPoint, 6);
        createPolygon(graphics, pen, startPoint, e.Location, 6);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }
    else if (draw && choice == 4)
    {
        createPolygon(graphics, eraser, startPoint, endPoint, 4);
        createPolygon(graphics, pen, startPoint, e.Location, 4);
        endPoint = e.Location;
        pictureBox1.Refresh();

    }
    else if (draw && choice == 5)
    {
        graphics.DrawLine(eraser, startPoint, endPoint);
        graphics.DrawLine(pen, startPoint, e.Location);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }
    else if (draw && choice == 6)
    {
        graphics.DrawRectangle(eraser, startPoint.X, startPoint.Y, endPoint.X - startPoint.X, endPoint.X - startPoint.X);
        graphics.DrawRectangle(pen, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }

    else if (draw && choice == 7)
    {
        graphics.DrawEllipse(eraser, startPoint.X, startPoint.Y, endPoint.X - startPoint.X, endPoint.X - startPoint.X);
        graphics.DrawEllipse(pen, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }
    else if (draw && choice == 8)
    {

        Point[] point2 = { new Point(startPoint.X, startPoint.Y), new Point(startPoint.X, endPoint.Y), new Point(endPoint.X, endPoint.Y) };
        Point[] point = { new Point(startPoint.X, startPoint.Y), new Point(startPoint.X, e.Y), new Point(e.X, e.Y) };
        graphics.DrawPolygon(eraser, point2);
        graphics.DrawPolygon(pen, point);
        endPoint = new Point(e.X, e.Y); // Update endPoint here
        pictureBox1.Refresh();
    }
    else if (draw && choice == 9)
    {

        Point[] point4 = { new Point(startPoint.X, startPoint.Y), new Point((startPoint.X + endPoint.X) / 2, endPoint.Y), new Point(endPoint.X, startPoint.Y) };
        Point[] point3 = { new Point(startPoint.X, startPoint.Y), new Point((startPoint.X + e.X) / 2, e.Y), new Point(e.X, startPoint.Y) };
        graphics.DrawPolygon(eraser, point4);
        graphics.DrawPolygon(pen, point3);
        endPoint = new Point(e.X, e.Y); // Update endPoint here
        pictureBox1.Refresh();
    }
    else if (draw && choice == 10)
    {


        graphics.DrawEllipse(eraser, startPoint.X, startPoint.Y, endPoint.X - startPoint.X, endPoint.X - startPoint.X);
        graphics.DrawEllipse(eraser, startPoint.X - 20, startPoint.Y - 20, (endPoint.X - startPoint.X) + 40, (endPoint.X - startPoint.X) + 40);
        graphics.DrawEllipse(pen, startPoint.X, startPoint.Y, e.X - startPoint.X, e.X - startPoint.X);
        graphics.DrawEllipse(pen, startPoint.X - 20, startPoint.Y - 20, (e.X - startPoint.X) + 40, (e.X - startPoint.X) + 40);
        endPoint = e.Location;
        pictureBox1.Refresh();
    }

} //and the code that follows is the code that draws the shapes in the g graphics
private void pictureBox1_Paint_1(object sender, PaintEventArgs e)
{
    foreach (var shape in shapes)
    {
        DrawShape(e.Graphics, shape);
    }
}
private void DrawShape(Graphics g, Shape shape)
{

    switch (shape.Type)
    {
        case 1:
            g.DrawRectangle(new Pen(shape.PenColor, 3), new Rectangle(shape.StartPoint, new Size(shape.EndPoint.X - shape.StartPoint.X, shape.EndPoint.Y - shape.StartPoint.Y)));
            break;
        case 2:
            g.DrawEllipse(new Pen(shape.PenColor, 3), new Rectangle(shape.StartPoint, new Size(shape.EndPoint.X - shape.StartPoint.X, shape.EndPoint.Y - shape.StartPoint.Y)));
            break;
        case 3:
            // Add logic for drawing hexagon (6-sided polygon)
            createPolygon(g, new Pen(shape.PenColor, 3), shape.StartPoint, shape.EndPoint, 6);
            break;
        case 4:
            // Add logic for drawing square (4-sided polygon)
            createPolygon(g, new Pen(shape.PenColor, 3), shape.StartPoint, shape.EndPoint, 4);
            break;
        case 5:
            g.DrawLine(new Pen(shape.PenColor, 3), shape.StartPoint, shape.EndPoint);
            break;
        case 6:
            g.DrawRectangle(new Pen(shape.PenColor, 3), new Rectangle(shape.StartPoint, new Size(shape.EndPoint.X - shape.StartPoint.X, shape.EndPoint.X - shape.StartPoint.X)));
            break;
        case 7:
            g.DrawEllipse(new Pen(shape.PenColor, 3), new Rectangle(shape.StartPoint, new Size(shape.EndPoint.X - shape.StartPoint.X, shape.EndPoint.X - shape.StartPoint.X)));
            break;
        case 8:
            createPolygon(g, new Pen(shape.PenColor, 3), shape.StartPoint, shape.EndPoint, 3);
            break;
        case 9:
            createPolygon(g, new Pen(shape.PenColor, 3), shape.StartPoint, shape.EndPoint, 3);
            break;
        case 10:
            // Add logic for drawing concentric circles
            g.DrawEllipse(new Pen(shape.PenColor, 3), new Rectangle(shape.StartPoint, new Size(shape.EndPoint.X - shape.StartPoint.X, shape.EndPoint.X - shape.StartPoint.X)));
            g.DrawEllipse(new Pen(shape.PenColor, 3), new Rectangle(new Point(shape.StartPoint.X - 20, shape.StartPoint.Y - 20), new Size(shape.EndPoint.X - shape.StartPoint.X + 40, shape.EndPoint.X - shape.StartPoint.X + 40)));
            break;
    }
}

内容的提问来源于stack exchange，提问作者Andrew Sempros