Once this is done, we will look at implementing any changes required to support these menus.

The following table details the steps required:

ASSIGN THE TYPE AND ORDER FOR OUR FILE MENUS

The key points here are the fact that the New and Open menus in the ParentForm class replace those in the MainForm class, and the merge order for each menu must match the desired position we discussed earlier. One other interesting point is the reuse of the Exit menu in the MainForm class for the Close menu in the merged menu. This makes sense, although we still need to rename the menu text to read

“Close” rather than “Exit.” We will do this in a way that continues to preserve the SDI application from part 2.

CHANGE THE EXIT MENU TEXT WHEN RUNNING AS AN MDI CHILD FORM

This change ensures that the Exit menu displays “Close” when the MainForm object is created as an MDI child window. Otherwise, the default setting of “Exit” will be used.

Compile and run the application to verify that our changes produce the appropriate menu structure. Create a new MDI child window and display the File menu. Your application should appear as in figure 16.5. Note how all the menus are now in the desired order, including the separator menus. Also note that the Exit menu from the MainForm class is reincarnated as the Close menu in the MDI application.

Figure 16.5 The merged File menu here gives no indication that different menu items are processed in different classes.

Of course, the Open menu is not yet implemented for our ParentForm class. Also note that the Toolbar control in our child window still provides access to the now hidden New and Open menus in the MainForm class.

We will deal with our toolbar shortly. First, let’s discuss our new Open menu.

16.3.3OPENING A CHILD FORM

The Open menu in the parent form should work much like the now hidden Open

menu for the MainForm class. The handler for this menu should display an OpenFileDialog and create a new child window containing the selected album. To create the MainForm instance, we will create a new constructor that accepts an album file name with which to initialize the window.

The code required here is nothing new to us, so let’s get to it.

IMPLEMENT HANDLER FOR OPEN MENU IN PARENT FORM

IMPLEMENT HANDLER FOR OPEN MENU IN PARENT FORM (continued)

The code displays an open file dialog and creates a child window using the selected album file. This code requires a new constructor for the MainForm class, namely one that accepts the file name of a photo album.

In this new constructor, we would like to make use of the constructor code already present in the existing constructor. We can do this in C# by simply invoking the default constructor with the this keyword. The following table illustrates this syntax, and the changes required for our new constructor.

CREATE A MAINFORM CONSTRUCTOR THAT ACCEPTS AN ALBUM FILE

6In the MainForm.cs file, create a public MainForm(string albumFile) new constructor that accepts

the name of an album file.

These changes permit the ParentForm class to create a new child window containing an open album. Compile and run the application to verify that this works as expected. The File menu from our two classes is now fully merged, and all menus are fully implemented.

As can be seen from this discussion, the ability to merge menus provides a powerful mechanism for controlling the menu bar in MDI applications. They permit the exact placement of menu items, and control over which class, the parent or child, will process each item. While we only merged a single menu here, you may find in your