使用DX811控件，Winform的Mdi中子窗体只打开一次。

使用dx8.11控件，Winform的Mdi中打开一次窗口，代码如下：

#region 打開窗口
private void OpenForm(string ChildTypeString)
{
DevExpress.Utils.WaitDialogForm wf = new DevExpress.Utils.WaitDialogForm("請等待......", "數據加載中：", new Size(300, 80));
DevExpress.XtraEditors.XtraForm myChild = null;
if (!ContainMDIChild(ChildTypeString))
{
try
{
Assembly assembly = Assembly.GetExecutingAssembly();
Type typForm = assembly.GetType(ChildTypeString);
Object obj = typForm.InvokeMember(null,
BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic |
BindingFlags.Instance | BindingFlags.CreateInstance,
null, null, null);

if (obj != null)
{
myChild = obj as DevExpress.XtraEditors.XtraForm;
myChild.MdiParent = this;
myChild.Show();
myChild.Focus();
}
}
catch //(Exception x)
{
//MessageBox.Show(x.ToString());
}
}
wf.Close();
}

private bool ContainMDIChild(string ChildTypeString)
{
DevExpress.XtraEditors.XtraForm myMDIChild = null;
foreach (DevExpress.XtraEditors.XtraForm f in this.MdiChildren)
{
if (f.GetType().ToString() == ChildTypeString)
{
myMDIChild = f;
break;
}
}

if (myMDIChild != null)
{
myMDIChild.TopMost = true;
myMDIChild.Show();
myMDIChild.Focus();
return true;
}
else
{
return false;
}
}
#endregion

=========================

调用方式：OpenForm(typeof(FrmUser).ToString());

附：一次运行一个实例：

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Threading;

namespace Attend
{
static class Program
{
/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);

bool bCreatedNew = false;
Mutex m = new Mutex(false, "HongKongAttend", out bCreatedNew);
if (bCreatedNew)
{
FrmLogin frmLogin = new FrmLogin();
frmLogin.ShowDialog();

if (frmLogin.DialogResult.Equals(DialogResult.OK))
{
Application.Run(new FrmMain());
}
}
else
{
MessageBox.Show("系統中已有此實例運行！", "系統提示：", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
}
}