C# 0 The Complete Reference

MainMenu

and

MenuItem

 inherit the 

Menu

 class.

When a menu item is selected, a 

Click

 event is generated. 

Click

 is defined by 

MenuItem

.

Therefore, to handle a menu selection, your program will add its handler to the 

Click

 event 

list for that item.

Each form has a 

Menu

 property, which is defined like this:

public MainMenu Menu { get; set; }

By default, no menu is assigned to this property. To display a main menu, this property 

must be set to the menu that you create.

Creating a main menu is straightforward, but it does involve several steps. Here is the 

approach we will use:

 1. 

Create 

a 

MainMenu

 object.

 2. 

To 

the 

MainMenu

 object, add 

MenuItem

s that describe the top-level categories. 

This is done by calling 

Add( )

 on the collection referred to by the 

MenuItems

property.

 

3.  To each top-level 

MenuItem

, add the list of 

MenuItem

s that defines the drop-down 

menu associated with that top-level entry. This is also done by calling 

Add( )

 on the 

collection referred to by the 

MenuItems

 property.

 

4.  Add the event handlers for each selection.

 5. 

Assign 

the 

MainMenu

 object to the 

Menu

 property associated with the form.

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The following sequence shows how to create a File menu that contains three selections: 

Open, Close, and Exit:

// Create a main menu object.

MainMenu MyMenu  = new MainMenu();

// Add a top-level menu item to the menu.

MenuItem m1 = new MenuItem("File");

MyMenu.MenuItems.Add(m1);

// Create File submenu.

MenuItem item1 = new MenuItem("Open");

m1.MenuItems.Add(item1);

MenuItem item2 = new MenuItem("Close");

m1.MenuItems.Add(item2);

MenuItem item3 = new MenuItem("Exit");

m1.MenuItems.Add(item3);

Let’s examine this sequence carefully. It begins by creating a 

MainMenu

 object called 

MyMenu

. This object will be at the top of the menu structure. This object is instantiated by 

use of the default constructor for 

MainMenu

. This creates an empty menu.

Next, a menu item called 

m1

 is created. This is the File heading. It is created by using 

this

MenuItem

 constructor:

public MenuItem(string 

caption

)

Here, 

caption

 specifies the text that is displayed by the item. In this case, it is “File.” This 

menu item is then added directly to 

MyMenu

 and is a top-level selection.

Notice that when 

m1

 is added to 

MyMenu

, it is done through the read-only 

MenuItems

property. 

MenuItems

 is a collection of the menu items that form a menu. It is defined by 

Menu

, which means it is part of both the 

MainMenu

 and 

MenuItem

 classes. It as shown here:

public Menu.MenuItemCollection MenuItems { get; }

To add a menu item to a menu, call 

Add( ) 

on

MenuItems

, passing in a reference to the item 

to add, as the example shows.

Next, the drop-down menu associated with File is created. Notice that these menu items 

are added to the File menu item, 

m1

. When one 

MenuItem

 is added to another, the added 

item becomes part of the drop-down menu associated with the item to which it is added. 

Thus, after the items 

item1

 through 

item3

 have been added to 

m1

, selecting File will cause a 

drop-down menu containing Open, Close, and Exit to be displayed.

Once the menu has been constructed, the event handlers associated with each entry 

must be assigned. As explained, a user making a selection generates a 

Click

 event. Thus, the 

following sequence assigns the handlers for 

item1

 through 

item3

.

// Add event handlers for the menu items.

item1.Click += MMOpenClick;

item2.Click += MMCloseClick;

item3.Click += MMExitClick;

Therefore, if the user selects Exit, 

MMExitClick( )

 is executed.

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