我现在是想通过按键让直线每次左移5个像素，具体代码如下。运行 结果发现只有第一次按键有效，之后每次按键直线都不动，这是为什么？请大侠帮忙，多谢！
private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            int temp = 5;
            if (linestate == true)
            {
                label1.Text = e.KeyValue.ToString();
                if (e.KeyValue.ToString().Equals("74"))
                {
                    Graphics g = this.CreateGraphics();
                    Pen mypen = new Pen(Color.Blue, 5);
                    g.Clear(Color.FromArgb(240, 240, 240));
                    g.DrawLine(mypen, 100 - temp, 100, 300 - temp, 100);
                }
            }
        }

没有刷新

this.Refresh();

   private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            
            int temp = 5;
            if (linestate == true)
            {
                label1.Text = e.KeyValue.ToString();
                if (e.KeyValue.ToString().Equals("74"))
                {
                    this.Refresh();
                    Graphics g = this.CreateGraphics();
                    Pen mypen = new Pen(Color.Blue, 5);
                    g.Clear(Color.FromArgb(240, 240, 240));
                    g.DrawLine(mypen, 100 - temp, 100, 300 - temp, 100);
                }
            }
            
        }

我试过了，没用

temp=0;
  private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            
            int temp = 5;
            if (linestate == true)
            {
                label1.Text = e.KeyValue.ToString();
                if (e.KeyValue.ToString().Equals("74"))
                {
                    this.Refresh();
                    Graphics g = this.CreateGraphics();
                    Pen mypen = new Pen(Color.Blue, 5);
                    g.Clear(Color.FromArgb(240, 240, 240));
                    g.DrawLine(mypen, 100 - temp, 100, 300 - temp, 100);
                    temp+=5；

                }
            }
            
        }