A forward declaration tells the C++ compiler that a class exists, without giving all the detail that a class definition (usually located in a header file of its own) provides. Lines 4 to 7 are forward declarations of the Qt classes that we will use to implement the dialog. Line 3 includes the definition of QDialog, the base class for dialogs in Qt. Lines 1 and 2 (and 27) protect the header file against multiple inclusions. The source code is spread across two files: finddialog.h and finddialog.cpp. By doing so, we make it an independent, self-contained component, with its own signals and slots. We will implement the dialog as a class in its own right. Our first example is a Find dialog written entirely in C++. Using Qt Designer is a lot faster than hand-coding and makes it easy to test different designs and to change designs later. Then we will see how to build dialogs using Qt Designer, Qt's visual design tool. We will create our first dialog purely by writing code to show how it is done. It is also possible to create dialog applications that respond directly to the user's choices by performing the appropriate actions (e.g., a calculator application). Most GUI applications consist of a main window with a menu bar and toolbar, along with dozens of dialogs that complement the main window. They are called dialog boxes, or simply "dialogs", because they provide a means by which users and applications can "talk to" each other. ![]() Dialog boxes present users with options and choices, and allow them to set the options to their preferred values and to make their choices. This chapter will teach you how to create dialog boxes using Qt. C++ GUI Programming with Qt4, 2nd Edition
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