In this tutorial I will explain what is MDI and how to use it in C#.

MDI (Multiple Document Interface) is a type of GUI (Graphical User Interface), which presents a single parent (container) window for other windows in a specific application. The opposites of MDI are SDI (Single Document Interface) and TDI (Tabbed Document Interface).

The main advantages of MDI are:

• Child windows are easily managed from a single parent (container) form.
• A single menu and toolbar can be shared for other windows.
• The possibility to work with multiple documents in one window of the same application.
• Closing the parent (container) window, the user closes other child windows.

Special Tutorial Requirements:

• C# IDE (Visual Studio 2008 used in this tutorial)
• .NET Framework 1.0

So, let's start creating an MDI application.

1. Create a standard C# Windows Forms Application:



2. First of all I have to create a container form. The first form that was created by default can become a container just by changing the IsMdiContainer property to True:



Now, the form should look like this:



3. Now, I will add a new form to the project. It will be a child form. To add a new form, use the Add New Item button on the IDE toolbar (if you use Visual Studio). Select the Add Windows Form... option from the dropdown menu:



4. Now, when a new form is created, I need to call it from the parent form, so I will create a menu on the first form, using the MenuStrip control:



5. To the newly created menu I will add a root element (I will call it "Container") and a child element (called "New Child..."):



6. Now, to open a new child in the parent form, add this code to the "New Child..." menu item:



Now, if you compile the application and click several times on the "New Child..." menu item, you will get new child forms inside the parent form:



7. Now, I will add some additional menu items, that will have the functionality needed to arrange the child forms inside the parent form.

Basically, there are four types of arrangement:

• Cascade
• Tile Horizontal
• Tile Vertical
• Arrange Icons

So, add the new menu items (as in the image below):



Here goes the code for all the types of arrangements (add this code to the corresponding menu items):

Cascade



Screenshot:



Tile Horizontal



Screenshot:



Tile Vertical



Screenshot:



Arrange Icons



Screenshot:



Note: the ArrangeIcons layout is available only for minimized child forms.

8. Now, if the user opens many child forms, it becomes harder to navigate between them, so I will set the MdiWindowListItem of the menu strip to windowToolStripMenuItem, so all opened child windows will be listed in the Window menu:



As the application starts and child windows are open, these are listed in the Window menu:



Now I can easily switch between all opened child windows.

This tutorial shows only the basics of creating a MDI application, but it also shows some fundamental MDI ideas and implementations.