的DrawLine不会出现

Question

当鼠标移到面板上时，我试图画一条垂直线：

private void panel1_MouseMove(object sender, MouseEventArgs e)
{
    Panel panel = sender as Panel;
    if (panel != null)
    {
        using (Graphics g = panel.CreateGraphics())
        {
            using (Pen pen = new Pen(Color.Red))
            {
                g.DrawLine(pen, e.X, 0, e.X, panel.Height);
            }
        }
        panel.Invalidate(true);
    }
}

但是，没有什么被吸入。

我在做什么错了？

Answer 1

所有GDI绘图都必须在.Paint()参数内提供的Graphics对象的PaintEventArgs事件内完成。使用.MouseMove()存储鼠标值，并触发绘制事件。

尝试一下：

public partial class Form1 : Form
{
    Point mouse;
    MouseButtons buttons;

    public Form1()
    {
        InitializeComponent();
    }

    private void panel1_Paint(object sender, PaintEventArgs e)
    {
        if (sender is Panel panel)
        {
            var g = e.Graphics;
            g.DrawLine(Pens.Red, mouse.X, 0, mouse.X, panel.Height);
        }
    }

    private void panel1_MouseMove(object sender, MouseEventArgs e)
    {
        mouse=e.Location;
        buttons=e.Button;

        panel1.Refresh();
    }
}

这是结果：