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Also note that Visual Studio .NET, while providing an MDI-like interface, uses more of a TabControl look and feel for the set of displayed windows, or what might be called a Multiple Tabbed Documents Interface, or MTDI. In this style, multiple sets of windows are displayed as horizontal or vertical groups of tabs. Both the MSDI and MTDI approaches can be created using the .NET Framework as an alternative to the traditional MDI interface, although there is not really any direct support for these newer interfaces. As a result, implementing such interfaces requires much more effort from the developer. For our purposes, a traditional MDI application provides the means to discuss and demonstrate the manner in which the .NET Framework supports such applications. We will convert the existing MyPhotos application into the MDI application shown in figure 16.3. As you can see, this application will incorporate the Form classes we have created in part 2 of this book.

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While the preceding program is a very simple example, it does illustrate the essential nature of exception handling Since division by zero is illegal, the program cannot continue if a zero is entered for the second number In this case, the exception is handled by not performing the division (which would have caused abnormal program termination) and by notifying the user of the error The program then reprompts the user for two more numbers Thus, the error has been handled in an orderly fashion and the user may continue on with the program The same basic concepts will apply to more complex applications of exception handling Exception handling is especially useful for exiting from a deeply nested set of routines when a catastrophic error occurs In this regard, C++ s exception handling is designed to replace the rather clumsy C-based setjmp( ) and longjmp( ) functions The key point about using exception handling is to provide an orderly means of handling errors This means rectifying the situation, if possible

Figure 16.3 Our multiple document interface, created in this chapter, displays a selected set of photo albums within a single window.

Run-Time Type Identification (RTTI)

Using run-time type identification, you can determine the type of an object during program execution To obtain an object s type, use typeid You must include the header <typeinfo> in order to use typeid Its general form is shown here typeid(object) Here, object is the object whose type you will be obtaining typeid returns a reference to an object of type type_info that describes the type of object defined by object The type_info class defines the following public members:

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The reuse of our existing classes is possible because of the manner in which the Form class in general and MDI support in particular is integrated into the Windows Forms hierarchy. As we discussed in chapter 7, a Form object is a Control instance that happens to display an application window. For MDI applications, Form controls are contained by a parent Form. Of course, the contained forms can be resized and moved within their container, and can still display menus, toolbars, status bars, and other controls. As we shall see, the relationship between MDI parent and child forms is different than the relationship between control containers and controls. 528

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SUPPORT IN WINDOWS FORMS To provide some insight and perhaps some perspective on MDI applications, the following table lists a number of class members specific to the implementation of MDI applications in the .NET Framework. Of course, these members can be used for other purposes, and additional properties, methods, and events are certainly used in MDI applications. These events highlight many of the MDI-specific tasks that are often performed in this style interface. The table provides a short description of each member and a reference to the section in this chapter where more information on each item may be found.