如何更新我的代码，以便能够重新调整矩形大小？

Question

这个WinForm应用程序允许用户在PictureBox中绘制多个矩形，但是一旦绘制了矩形，就无法改变它。我希望所有矩形都能够重新调整大小，并最终实现撤消选项，但我现在主要关注的是重新调整大小。

我真的很困惑在哪里开始改变我的代码以包括重新调整大小。我想用我的矩形做this之类的事情。任何建议/协助将不胜感激！

我的代码：

public partial class Form1 : Form
{
   Point startPos;
   Point currentPos;
   bool drawing;
   List<Rectangle> myRectangles = new List<Rectangle>();

   public Form1()
   {
       InitializeComponent();
   }

   private void selectFileToolStripMenuItem_Click(object sender, EventArgs e)
   {
       try
       {
           //Initiate new OpenFileDialog
           //Filter for img and bmp files
           //Start looking in root of c:
           OpenFileDialog myFile = new OpenFileDialog();
           myFile.Filter = "Image Files(*.img, *.bmp) |*.img; *.bmp;";
           myFile.InitialDirectory = "c:\\";

           //Set background image of pictureBox to file selected through OpenFileDialog
           if (myFile.ShowDialog() == DialogResult.OK)
           {
               pictureBox1.BackgroundImage = Image.FromFile(myFile.FileName);
           }
       }

       catch (Exception error)
       {
           MessageBox.Show("Error loading the selected file.  Original error: " + error.Message);             
       }
   }

   private void exitToolStripMenuItem_Click(object sender, EventArgs e)
   {
       this.Close();
   }

   private void clearAllToolStripMenuItem_Click(object sender, EventArgs e)
   {
   }

   private void zoomToolStripMenuItem_Click(object sender, EventArgs e)
   {
   }

   private void undoLastActionToolStripMenuItem_Click(object sender, EventArgs e)
   {
   }

   private void redoLastActionToolStripMenuItem_Click(object sender, EventArgs e)
   {
   }

   private Rectangle getRectangle()
   {
        return new Rectangle(
           Math.Min(startPos.X, currentPos.X),
           Math.Min(startPos.Y, currentPos.Y),
           Math.Abs(startPos.X - currentPos.X),
           Math.Abs(startPos.Y - currentPos.Y));
   }

   private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
   {
       if (e.Button == MouseButtons.Left)
       {
           currentPos = startPos = e.Location;
           drawing = true;
       }       
   }

   private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
   {
       currentPos = e.Location;
       if (drawing) pictureBox1.Invalidate();
   }

   private void pictureBox1_Paint(object sender, PaintEventArgs e)
   {
       if (myRectangles.Count > 0) e.Graphics.DrawRectangles(Pens.Black, myRectangles.ToArray());
       if (drawing) e.Graphics.DrawRectangle(Pens.Red, getRectangle());
   }

   private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
   {
       if (drawing)
       {
           drawing = false;
           var rect = getRectangle();
           if (rect.Width > 0 && rect.Height > 0) myRectangles.Add(rect);
           pictureBox1.Invalidate();
       }
   }
}