C# ImageBox 在 MouseUp 上清除矩形

我有一个面板，其中包含在运行时创建的多个图片框。

用户将在任何图片框上创建一个矩形，所选部分将显示在预览图片框上。

我已经使用下面的代码成功完成了上述操作。

Question

1. 我想在 mouseup 事件中清除选择矩形。使用无效但不起作用。 从如何清除图片框中的图形（矩形） https://stackoverflow.com/questions/10442279/how-to-clear-the-graphicsrectangle-shape-in-picturebox

2. 另外，当我滚动面板时，所有图片框上都会显示相同的矩形（鼠标选择）。

       private void Picture_Paint(object sender, PaintEventArgs e)
   {
       if (Rect!=null && Rect.Width>0 && Rect.Height>0)
       {
           e.Graphics.FillRectangle(selectionBrush, Rect);
       }
   }
   
   private void Picture_MouseDown(object sender, MouseEventArgs e)
   {
       RecStartpoint = e.Location;
       ((PictureBox)sender).Invalidate();
   }
   
   private void Picture_MouseMove(object sender, MouseEventArgs e)
   {
       if (e.Button != MouseButtons.Left) return;
   
       Point tempEndPoint = e.Location;
       Rect.Location = new Point(
           Math.Min(RecStartpoint.X, tempEndPoint.X),
           Math.Min(RecStartpoint.Y, tempEndPoint.Y));
       Rect.Size = new Size(
           Math.Abs(RecStartpoint.X - tempEndPoint.X),
           Math.Abs(RecStartpoint.Y - tempEndPoint.Y));
       ((PictureBox)sender).Invalidate();
   }
   
   private void Picture_MouseUp(object sender, MouseEventArgs e)
   {
       if (e.Button != MouseButtons.Left) return;
   
       PictureBox org_pic = (PictureBox)(sender);
   
       Point RecEndpoint=e.Location;
   
   
       int xDown = Math.Min(RecStartpoint.X,RecEndpoint.X);
       int yDown = Math.Min(RecStartpoint.Y, RecEndpoint.Y);
       int xUp = Math.Max(RecStartpoint.X,RecEndpoint.X);
       int yUp = Math.Max(RecStartpoint.Y,RecEndpoint.Y);
   
       Rectangle rec = new Rectangle(xDown, yDown, Math.Abs(xUp - xDown), Math.Abs(yUp - yDown));
   
       xDown = xDown * org_pic.Image.Width / org_pic.Width;
       yDown = yDown * org_pic.Image.Height / org_pic.Height;
   
       xUp = xUp * org_pic.Image.Width / org_pic.Width;
       yUp = yUp * org_pic.Image.Height / org_pic.Height;
   
       rectCropArea = new Rectangle(xDown, yDown, Math.Abs(xUp - xDown), Math.Abs(yUp - yDown));
   
       pictureBox_preview_photo.Refresh();
       Bitmap sourceBitmap = new Bitmap(org_pic.ImageLocation);
       Graphics g = pictureBox_preview_photo.CreateGraphics();
       g.DrawImage(sourceBitmap, new Rectangle(0, 0, pictureBox_preview_photo.Width, pictureBox_preview_photo.Height), rectCropArea, GraphicsUnit.Pixel);
   
   }
   

我会尝试这种方法：

首先，使Image变量，在形式范围内

public partial class Form1 : Form
{
    //variable for holding original image, before rectangle is drawn on it
    Image originalImage = null;

    public Form1()
    {
        InitializeComponent();
    }
    //rest of form's code...

其次，将当前图片保存在该变量中MouseDown

private void Picture_MouseDown(object sender, MouseEventArgs e)
{
    //save it
    startImage = ((PictureBox)sender).Image;
    RecStartpoint = e.Location;
    ((PictureBox)sender).Invalidate();
}

最后，在结束时MouseUp事件、设置Rectangle的宽度和高度为零并恢复保存的原始图像

//snipped code
pictureBox_preview_photo.Refresh();
Bitmap sourceBitmap = new Bitmap(org_pic.ImageLocation);
Graphics g = pictureBox_preview_photo.CreateGraphics();
g.DrawImage(sourceBitmap, new Rectangle(0, 0, pictureBox_preview_photo.Width, pictureBox_preview_photo.Height), rectCropArea, GraphicsUnit.Pixel);

//make rectangle's widht and height 0 so that Paint event won't draw it
Rect.Width = Rect.Height = 0;
//restore image
this.Picture.Image = startImage;

我不明白第二个问题。