一个简单的绘图问题

Question

//功能是：我希望绘制的图像会随着窗体的大小变化而变化，并且铺满整个窗体。问题是我每次改变窗体大小时，原来绘制的图像还在，而且在上层。但是如果将
窗体最小化或是被其它窗体遮挡，再恢复后就是正常的。我原来想加一句dc.Clear(Color.Black );又会出现参数错误的提示，到底如何改呢？谢谢 代码是这样的：public partial class Form2 : Form
    {
        Image piccy;
        Point[] piccb;
        Graphics dc;
        public Form2()
        {
            InitializeComponent();
            piccy = Image.FromFile("..\\..\\1\\l.jpg");
            this.AutoScrollMinSize = piccy.Size;
            piccb = new Point[3];
            piccb[0]=new Point (0,0);
            piccb[1] = new Point(this.Width , 0);
            piccb[2] = new Point(0, this.Height );
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
             dc = e.Graphics;
            dc.ScaleTransform(1f,1f);
            dc.TranslateTransform(this.AutoScrollPosition.X, this.AutoScrollPosition.Y);
            dc.DrawImage(piccy, piccb);
        }        
        private void Form2_SizeChanged_1(object sender, EventArgs e)
        {
            //dc.Clear(Color.Black );
            piccb[0] = new Point(0, 0);
            piccb[1] = new Point(this.Width, 0);
            piccb[2] = new Point(0, this.Height);        }
        
    }

Answer 1

public partial class Form2 : Form
{
    Image piccy;     public Form2() 
    { 
        InitializeComponent(); 
        piccy = Image.FromFile("..\\..\\1\\l.jpg"); 
        this.DoubleBuffered = true;
        this.AutoSize = true;
        this.AutoScrollMinSize = piccy.Size;
    }     protected override void OnPaint(PaintEventArgs e) 
    {
        Graphics dc = e.Graphics;
        dc.TranslateTransform(this.AutoScrollPosition.X, this.AutoScrollPosition.Y);
        dc.DrawImage(piccy, this.ClientRectangle);                          //<--
    }    protected override void OnResize(EventArgs e)
    {
        base.OnResize(e);
        this.Invalidate();                                                  //<--
        this.Update();
    }
几个建议，一是不要缓存Graphic对象，二是窗体（含边框，标题栏）比客户区大，用客户区大小比较合适。

Answer 2

SizeChange之后调用this.Invalidate();重绘一下

Answer 3

特别感谢gomoku的解答
也谢谢tinghai_xu