正在阅读：MDI应用中的单实例(singleton)窗口MDI应用中的单实例(singleton)窗口

private void toolBar1_ButtonClick(object sender,
     System.Windows.Forms.ToolBarButtonClickEventArgs e)
{
    // a flag to store if the child form is opened or not
    bool found = false;
 
    if (e.Button == toolBarButton1)
    {
       // get all of the MDI children in an array
       Form[] charr = this.MdiChildren;
 
       if (charr.Length == 0)      // no child form is opened
       {
          Patients myPatients = new Patients();
          myPatients.MdiParent = this;
          // The StartPosition property is essential
          // for the location property to work
          myPatients.StartPosition = FormStartPosition.Manual;
          myPatients.Location = new Point(0,0);
          myPatients.Show();
        }
        else      // child forms are opened
        {

         foreach (Form chform in charr)
          {
            if (chform.Name == "Patients")
            // one instance of the form is already opened
            {
              chform.Activate();
              found = true;
              break;   // exit loop
            }
            else
              found = false;      // make sure flag is set to
                                  // false if the form is not found
          }
 
          if (found == false)   
          {
            Patients myPatients = new Patients();
            myPatients.MdiParent = this;
            // The StartPosition property is essential
            // for the location property to work
            myPatients.StartPosition = FormStartPosition.Manual;
            myPatients.Location = new Point(0,0);
            myPatients.Show();
          }
        }
    }
}