需要引用：

using System.Windows.Forms;
using System.Drawing;

 1 public partial class App : System.Windows.Application
 2     {
 3         protected override void OnStartup(StartupEventArgs e)
 4         {
 5 
 6             base.OnStartup(e);
 7             MainWindow w1 = new MainWindow();//主窗口
 8             RevealWindow w2 = new RevealWindow();//副窗口
 9             if (Screen.AllScreens.Length > 1)
10             {
11                 
12                 Screen s1 = Screen.AllScreens[0];//主屏幕
13                 Screen s2 = Screen.AllScreens[1];//副屏幕
14                 Rectangle r1 = s1.WorkingArea;
15                 Rectangle r2 = s2.WorkingArea;
16 　　　　　　　　　　//因为我的主副屏幕是反的所以主窗口放入副屏幕中。

17                 //主窗口放入副屏幕中
18                 w1.Top = r2.Top;
19                 w1.Left = r2.Left;
20                 //副窗口放入主屏幕中
21                 w2.Top = r1.Top;
22                 w2.Left = r1.Left;
23 
24                 w1.Show();
25                 w2.Show();
26 
27                 w2.Owner = w1;
28             }
29         }
30     }