Question

C#用picturebox画坐标轴

private void Form1_Paint(object sender, PaintEventArgs e)
{
Graphics g = Graphics.FromHwnd(this.pictureBox2.Handle);
Pen pen2 = new Pen(Color.Black,2);
g.DrawLine(pen2, 120, 100, 120, 350);
g.DrawLine(pen2, 120, 350, 370, 350);
Pen p = new Pen(Color.Blue,2);
p.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;
g.DrawLine(p, 370, 100, 370, 350);
Pen pen3 = new Pen(Color.Black, 5);
g.DrawEllipse(pen3, 150, 368, 2, 2);
Pen pen4 = new Pen(Color.Red, 5);
g.DrawEllipse(pen4, 250, 368, 2, 2);
}
这样写可以吗？可是运行时为什么不能显示？

Answer 1

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
Graphics g = e.Graphics;
Pen pen2 = new Pen(Color.Black, 2);
g.DrawLine(pen2, 120, 100, 120, 350);
g.DrawLine(pen2, 120, 350, 370, 350);
Pen p = new Pen(Color.Blue, 2);
p.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;
g.DrawLine(p, 370, 100, 370, 350);
Pen pen3 = new Pen(Color.Black, 5);
g.DrawEllipse(pen3, 150, 368, 2, 2);
Pen pen4 = new Pen(Color.Red, 5);
g.DrawEllipse(pen4, 250, 368, 2, 2);
}
这样就可以啦。

追问

只有黑色和蓝色两条纵坐标轴其它的不见了

追答

你的PictureBox的大小要足够大赛，小了，你肯定看不到。

Answer 2

代码没问题，问题出在Paint事件上，你可以仔细查下paint事件的发生时机

可以把这些代码放在click事件下，然后点击进行测试：
private void pictureBox2_Click(object sender, EventArgs e)
{
………………
}

追问

这样的话就一定要单击才能显示咯？

追答

是的，要想一直显示，好像不能直接添加，试试等窗体加载完毕后再把paint事件添加给form

不改变的话拖动改变窗体大小（触发了paint事件）能看到你的绘图效果