程序代码：

  private bool isMouseDown = false;
        private int mouseX = 0;
        private int baseWidth = 0;
        private void listBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isMouseDown)
            {
                this.listBox1.Width = baseWidth + e.X - mouseX;
                if (this.listBox1.BorderStyle != BorderStyle.FixedSingle)
                {
                    this.listBox1.BorderStyle = BorderStyle.FixedSingle;
                }
            }
            else
            {
                int n = Math.Abs(e.X - this.listBox1.Width);
                this.label1.Text = n.ToString();
                if (n < 10)
                {
                    if (this.Cursor != Cursors.SizeWE)
                    {
                        this.listBox1.Cursor = this.Cursor = Cursors.SizeWE;

                    }
                }
                else
                {
                    if (this.Cursor != Cursors.Default)
                        this.listBox1.Cursor = this.Cursor = Cursors.Default;
                }
            }
        }
        private void listBox1_MouseUp(object sender, MouseEventArgs e)
        {
            isMouseDown = false;
            if (this.listBox1.BorderStyle != BorderStyle.Fixed3D)
            {
                this.listBox1.BorderStyle = BorderStyle.Fixed3D;
            }
        }

        private void listBox1_MouseDown(object sender, MouseEventArgs e)
        {
            isMouseDown = true;
            baseWidth = this.listBox1.Width;
            mouseX = e.X;
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            listBox1_MouseMove(sender, e);
        }