c# - How to draw a line on panel? It is not showing up

Question

I have a Panel called panel1 and I am trying to draw a line on my panel1 using this code:

var g = panel1.CreateGraphics();
var p = new Pen(Color.Black, 3);

var point1 = new Point(234,118);
var point2 = new Point(293,228);

g.DrawLine(p, point1, point2);

But nothing is showing up. Any ideas? This is in a windows form.

Answer 1

处理 Panel 的Paint 事件并将其放入其中。发生的事情是它在构造函数中被绘制一次，但Paint每次被调用时都会在事件中被绘制。

private void panel1_Paint(object sender, PaintEventArgs e)
{
    base.OnPaint(e);
    using(Graphics g = e.Graphics)
    {
       var p = new Pen(Color.Black, 3);
       var point1 = new Point(234,118);
       var point2 = new Point(293,228);
       g.DrawLine(p, point1, point2);
    }
}

Answer 2

在表单创建并显示在屏幕上之后，将它放在某个事件中，它应该可以正常工作。

正如keyboardP所说，最好将它放在Paint事件中，但如果在屏幕上显示表单之前调用它，它将不会显示。

要对此进行测试，您可以添加一个按钮并将代码添加到单击事件中：

private void button1_Click(object sender, EventArgs e)
{
    using (Graphics g = panel1.CreateGraphics())
    {
        g.DrawLine(new Pen(Color.Back, 3), new Point(234,118), new Point(293,228));
    }
}

Answer 3

要查看您的绘图 - 您可以简单地制作一个带有 Click Event 的按钮并在单击该按钮时进行绘制。例如：

private void btnDraw_Click(object sender, EventArgs e)
{
    Graphics dc = drawingArea.CreateGraphics();
    Pen BlackPen = new Pen(Color.Black, 2);
    dc.DrawLine(BlackPen, 0, 0, 200, 200);

    BlackPen.Dispose();
    dc.Dispose();
}    

哦，顺便说一句，“drawingArea”是您添加到表单（在其中绘制）的 PictureBox 或 Panel 的（名称）。

Answer 4

如果您遵循其他答案并且仍然没有显示您的绘图，请尝试从正在绘制的控件中删除所有控件。其他控件可能会覆盖您尝试绘制的任何内容。

Answer 5

private void button2_Click(object sender, EventArgs e)
    {
        panel1.Paint += new PaintEventHandler(
            (object sender1, PaintEventArgs e1) => {
                var p = new Pen(Color.Black, 3);
                var point1 = new Point(234, 118);
                var point2 = new Point(293, 228);
                e1.Graphics.DrawLine(p, point1, point2);
            }
        );
        
        panel1.Invalidate();
        
    }