WinForm MDIParent如何防止重复打开

 1 using System;
 2 using System.Windows.Forms;
 3 
 4 namespace WinFormMDI
 5 {
 6     public partial class FrmMain : Form
 7     {
 8         public FrmMain()
 9         {
10             InitializeComponent();
11         }
12 
13         private void Child1ToolStripMenuItem_Click(object sender, EventArgs e)
14         {
15             ShowSingleWindow(typeof(FrmChild1));
16         }
17 
18         private void Child2ToolStripMenuItem_Click(object sender, EventArgs e)
19         {
20             ShowSingleWindow(typeof(FrmChild2));
21         }
22 
23         private void ShowSingleWindow(Type type)
24         {
25             foreach (Form f in this.MdiChildren)
26             {
27                 if (f.GetType() == type)
28                 {
29                     f.Activate();
30                     return;
31                 }
32             }
33 
34             Form frm = type.Assembly.CreateInstance(type.ToString()) as Form;
35             frm.MdiParent = this;
36             frm.WindowState = FormWindowState.Maximized;
37             frm.Show();
38         }
39     }
40 }