调试易

foreach(Form f in this.MdiChildren)
{
if ( f is FormB)
{
f.Show();
}
else
{
FormB formNew = new FormB();
formNew.MdiParent = this;
formNew.Show();
}
}

/// <summary>
        /// 定义子窗体变量
        /// </summary>
        private frmNewOrder frmneworder;
        private FrmSendOrder frmsendorder;        private void neworderToolStripMenuItem_Click(object sender, EventArgs e)
        {
            try
            {
                if (this.frmneworder == null || !this.frmneworder.Created)
                {                    this.frmneworder = new frmNewOrder();
                    this.frmneworder.MdiParent = this;
                    this.frmneworder.Show();
                }
                else
                {
                    this.frmneworder.Show();
                }
                this.frmneworder.Focus();
            }
            catch (Exception sysE)
            {
                MessageBox.Show(sysE.Message);
            }
        }

static void Main() 
{
Mutex mutex = new Mutex(false, "ThisShouldOnlyRunOnce");
//判断互斥体是否使用中。
bool Running = !mutex.WaitOne(0, false);
if (! Running) 
{
Application.Run(new Form1());
}
else   
{
MessageBox.Show("应用程序已经启动！","系统提示");
}
}
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