c# API找到指定窗口,在它上面画根线

[DllImport("User32.dll", EntryPoint = "FindWindow")] private static extern IntPtr FindWindow(string lpClassName, string lpWindowName); //添加引用 找到窗口句柄 private void button1_Click_1(object sender, EventArgs e) { IntPtr p = FindWindow("notepad", null); if (p == IntPtr.Zero) { MessageBox.Show("error!"); } else { Graphics g = Graphics.FromHwnd(p); g.DrawLine(new Pen(Color.Red), new Point(0, 0), new Point(200, 200)); } }