C# Winform实现在Pancel上绘制矩形

namespace VipSoft.ClientForm
{
    public partial class DemoFrm : Form
    {
        public DemoFrm()
        {
            InitializeComponent();
        }

        private void Demo_Load(object sender, EventArgs e)
        {
            ChartControl pnlControl = new ChartControl();
            pnlControl.Dock = DockStyle.Fill;
            pnlControl.Size = new Size(this.Width, this.Height);
            pnlControl.DrawChart();
            pnlDemo.Controls.Add(pnlControl);
        }
    }
}



public partial class ChartControl : UserControl
{
    public ChartControl()
    {
        DrawGrids();
    }
	
     //绘制网格
    private void DrawGrids()
    {
        //先加的控件，显示在最外面
        this.Controls.Add(new Label()
        {
            AutoSize = true,
            Top = 10,
            Left = 20,
            Text = "asdf",
            ForeColor = Color.BlueViolet,
            Font = new System.Drawing.Font("宋体", 36F)
        });


        this.BackColor = Color.Red; 
        Panel pnlGrid = new Panel();
        //pnlGrid.BackColor = Color.Green;
        pnlGrid.Dock = DockStyle.Fill;
        pnlGrid.Paint += new PaintEventHandler(this.CustomPanel_Paint);
        this.Controls.Add(pnlGrid);
    }

    private void CustomPanel_Paint(object sender, PaintEventArgs e)
    {
        Graphics g = e.Graphics;
        // 示例：绘制一个红色的矩形
        g.FillRectangle(Brushes.Blue, 50, 50, 100, 100);
    }
}

private void DrawOnPanel(Panel panel)
{
    using (Graphics g = panel.CreateGraphics())
    {
        // 示例：绘制一个蓝色的椭圆
        g.FillEllipse(Brushes.Blue, 25, 25, 150, 100);
    }
}

private Bitmap offscreenBitmap; // 用于双缓冲的位图
private void CustomPanel_Paint(object sender, PaintEventArgs e)
{
    if (offscreenBitmap == null) // 初始化位图缓冲区
    {
        offscreenBitmap = new Bitmap(this.Width, this.Height);
    }
    using (Graphics g = Graphics.FromImage(offscreenBitmap)) // 使用位图创建Graphics对象
    {
        g.Clear(this.BackColor); // 清除背景色
        // 在这里绘制你的图形，例如：
        g.FillRectangle(Brushes.Green, 50, 50, 100, 100); // 示例：绘制一个绿色的矩形
    }
    e.Graphics.DrawImage(offscreenBitmap, Point.Empty); // 将位图绘制到控件上
}

private void Demo_Load(object sender, EventArgs e)
{
    pnlDemo.Controls.Clear();

    EcgGridChartControl overviewControl = new EcgGridChartControl();
    overviewControl.Dock = DockStyle.Fill;
    overviewControl.DrawChart();
    overviewControl.Size=new Size(this.Width, this.Height);
    pnlDemo.Controls.Add(overviewControl);
}

public partial class ChartControl : UserControl
{

	protected override void OnLoad(EventArgs e)
	{
		DrawGrids();
	}

	//绘制网格
	private void DrawGrids()
	{
	    //先加的控件，显示在最外面
	    this.Controls.Add(new Label()
	    {
	        AutoSize = true,
	        Top = 10,
	        Left = 20,
	        Text = "asdf",
	        ForeColor = Color.BlueViolet,
	        Font = new System.Drawing.Font("宋体", 36F)
	    });


	    //this.BackColor = Color.LightSkyBlue;

	    //作为背景
	    Panel pnlGrid = new Panel();
	    //pnlGrid.BackColor = Color.Green;
	    pnlGrid.Dock = DockStyle.Fill;
	    pnlGrid.Paint += new PaintEventHandler(this.CustomPanel_Paint); 
	    this.Controls.Add(pnlGrid);

	    Panel pnlLine = new Panel();
	    pnlLine.BackColor = Color.Transparent;//将Panel设为透明
	    pnlLine.Dock = DockStyle.Fill;
	    pnlLine.Paint += new PaintEventHandler(this.CustomPanelBitmap_Paint);
	    pnlLine.Parent = picBox; //将panel父控件设为背景图片控件
	    pnlLine.BringToFront();//将panel放在前面

	    pnlGrid.Controls.Add(pnlLine);
	}

	private void CustomPanel_Paint(object sender, PaintEventArgs e)
	{
	    Graphics g = e.Graphics;

	    using (Pen pen = new Pen(Color.Black, 2))
	    {
	        g.DrawLine(pen, 10, 230, this.Width-10, 230); 
	    }
	}

	private Bitmap offscreenBitmap; // 用于双缓冲的位图
	private void CustomPanelBitmap_Paint(object sender, PaintEventArgs e)
	{
	    if (offscreenBitmap == null) // 初始化位图缓冲区
	    {
	        offscreenBitmap = new Bitmap(this.Width, this.Height);
	    }
	    using (Graphics g = Graphics.FromImage(offscreenBitmap)) // 使用位图创建Graphics对象
	    {
	        //g.Clear(this.BackColor); // 清除背景色
	        // 在这里绘制你的图形，例如：
	        g.FillRectangle(Brushes.Yellow, 200, 200, 100, 100); // 示例：绘制一个绿色的矩形
	    }
	    e.Graphics.DrawImage(offscreenBitmap, Point.Empty); // 将位图绘制到控件上
	}

}