Multiple Document Interface (MDI) applications have a single, primary window (the parent window) that contains a set of windows within its client region (child windows). Each child window is a form that is constrained to appear only within the parent. Children typically share the menu bar, tool bar, and other parts of the parent's interface. Secondary windows like dialog boxes are not constrained to the parent window's client region.

Creating an MDI Application

You can create an MDI application by following these steps:

  1. Create a Form (MainForm) that represents the MDI parent window and set its IsMdiContainer property to True. The following code demonstrates how to set this property.

set_is_mdi_container (True)

  1. Create child forms and set the MdiParent property of each form to reference the parent form. The following code demonstrates setting the MDI parent for an instance of a child form.

doc.set_mdi_parent (Current)

If you have different types of data to display, you can have multiple types of child forms. To display a child form, create an instance of the child form and call its Show method.

Standard MDI Menus

Typically, an MDI application has a Windows menu that allows the user to arrange the open child windows through tiling or cascading. The Windows menu also allows you to navigate to any of the open child windows. To create a Windows menu, add the menu items for tiling and cascading to a Windows menu in your parent form and set the MdiList property to True for the top-level Windows menu. The following code demonstrates how to create a Windows menu in an MDIapplication. mi_window: WINFORMS_MENU_ITEM ... mi_window := main_menu.get_menu_items.add ("&Window") dummy := mi_window.get_menu_items.add_string_event_handler ("&Cascade", create {EVENT_HANDLER}.make (Current, $window_cascade_clicked)) dummy := mi_window.get_menu_items.add_string_event_handler ("Tile &Horizontal", create {EVENT_HANDLER}.make (Current, $window_tile_h_clicked)) dummy := mi_window.get_menu_items.add_string_event_handler ("Tile &Vertical", create {EVENT_HANDLER}.make (Current, $window_tile_v_clicked)) mi_window.set_mdi_list (True) -- Adds the MDI Window List to the bottom of the menu ...

Child Window Activation

If you want your parent form to be notified when a child window is activated by the user, you can register an event-handling method for the MdiChildActivate event. You can determine which child window is active by using the ActiveMdiChild property of the Form class. For example, the following code updates a StatusBar control on the parent form with the name of the child window. ... add_mdi_child_activate (create {EVENT_HANDLER}.make (Current, $mdi_child_activated)) ... mdi_child_activated (sender: SYSTEM_OBJECT; e: EVENT_ARGS) do status_bar.set_text (active_mdi_child.get_text) end ...

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