MDI应用中的单实例(singleton)窗口

下面的代码片断假设你的多文档应用程序中包含一个toolbar。当你点击toolBarButton1 按钮时，将会创建并显示一个 Patients 子窗口。下面的代码在单机事件时发生。

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();

          }

        }

    }

}

这样，就实现了一个单窗口实例的解决方案。

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