在刷新/失效时保留在面板上绘制的内容

Question

这个问题相当简单。有没有办法在每次触发 Paint 事件时将绘制的内容保留在带有图形的面板上？

在一个简单的程序上演示：每 100 毫秒打开一次面板上的随机像素，直到面板全部着色。

Answer 1

简短的例子：

public partial class Form1 : Form
{
    private Bitmap bitmap;
    private Random random = new Random();
    public Form1()
    {
        InitializeComponent();
        bitmap = new Bitmap(panel1.Width,panel1.Height);
    }
    private void panel1_Paint(object sender, PaintEventArgs e)
    {
        e.Graphics.DrawImage(bitmap,new Point(0,0));
    }
    private void button1_Click(object sender, EventArgs e)
    {
        using (Graphics graphics = Graphics.FromImage(bitmap))
        {
            graphics.DrawLine(
                new Pen(new SolidBrush(Color.Black),1),
                new Point(random.Next(0, bitmap.Width), random.Next(0, bitmap.Width)),
                new Point(random.Next(0, bitmap.Width), random.Next(0, bitmap.Width)));
        }
        panel1.Invalidate(); // redraw
    }
}