c# - 以 MDI 形式多次防止同一个子窗口

Question

我正在开发 C# 桌面应用程序，在 MDI 窗体中，当您单击菜单时会打开同一个子窗口，同时显示该窗口的第一个实例。 如何防止 MDI 窗体中出现这些子窗口的多个实例？

Answer 1

您可以检查表单是否已经打开:

  Form instance = null;

  // Looking for MyForm among all opened forms 
  foreach (Form form in Application.OpenForms) 
    if (form is MyForm) {
      instance = form;

      break; 
    }

  if (Object.ReferenceEquals(null, instance)) {
    // No opened form, lets create it and show up:
    instance = new MyForm();
    instance.Show();
    ...
  }
  else {
    // MyForm has been already opened

    // Lets bring it to front, focus, restore it sizes (if minimized)
    if (instance.WindowState == FormWindowState.Minimized)
      instance.WindowState = FormWindowState.Normal; 

    instance.BringToFront();

    if (instance.CanFocus) 
      instance.Focus();
    ...
  }