DrawLine消失了

Question

Graphics g = this.panel1.CreateGraphics();
            Pen pen = new Pen(Color.Red,2);
            Point oldPoint = new Point();
            oldPoint.X = oldbtn.Location.X + oldbtn.Width;
            oldPoint.Y = oldbtn.Location.Y + oldbtn.Height / 2;
            Point newPoint = new Point();
            newPoint.X = newbtn.Location.X;
            newPoint.Y = newbtn.Location.Y + oldbtn.Height / 2;
            g.DrawLine(pen, newPoint, oldPoint);
为两个控件之间画上线  失去焦点后 线消失了  请问这个怎么解决呢？

Answer 1

1 放到Paint里
 private void Form1_Paint(object sender, PaintEventArgs e)
        {        }2 或则你绘制到图片上贴背景图.

Answer 2

把做图的语句放到OnPaint里
   protected override void OnPaint( PaintEventArgs e )
    {

Answer 3

        public Form2()
        {
            InitializeComponent();
            this.Paint += new System.Windows.Forms.PaintEventHandler(this.Form2Paint);
        }        private void Form2Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.panel1.CreateGraphics(); 
            Pen pen = new Pen(Color.Red,2); 
            Point oldPoint = new Point(); 
            oldPoint.X = oldbtn.Location.X + oldbtn.Width; 
            oldPoint.Y = oldbtn.Location.Y + oldbtn.Height / 2; 
            Point newPoint = new Point(); 
            newPoint.X = newbtn.Location.X; 
            newPoint.Y = newbtn.Location.Y + oldbtn.Height / 2; 
            g.DrawLine(pen, newPoint, oldPoint);         } 

Answer 4

为两个控件之间画上线  失去焦点后 线消失了
-------------------------------------
因为控件失去焦点，会刷新。如果你的画线操作没有和刷新挂勾的话，之前的线就不再出现。可以使用panel.OnPaint事件。