Application View Design
When developing an application with a graphical user interface, the main work takes place in providing a so-called "view" for the application. A view generally is a widget that displays the data of a document and provides methods to manipulate the document contents. This can be done by the user via the events he emits by the keyboard or the mouse; more complex operations are often processed by toolbars and menubars which interact with the view and the document. The statusbar then provides information about the document, view or application status. As an example, we look at how an editor is constructed and where we can find which part.
An editor generally is supposed to provide an interface to view and/or change the contents of a text document for the user. If you start Kate, you see the visual interface as the following:
The menubar: providing complex operations as well as opening, saving and closing files and exiting the application.
The toolbar: offers icons which allow quicker access for most needed functions,
The statusbar: displays the status of the cursor position by the current row and column,
The view in the center of the window, displaying a document and offering a cursor connected to the keyboard and the mouse to operate on the data.
Now it's easy to understand that a view is the most unique part of the application and the design of the view decides about the usability and acceptability of an application. This means that one of the first steps in development is to determine the purpose of the application and what kind of view design would match best to allow any user to work with the application with a minimum of work learning how to handle the user interface.
For some purposes like text editing and displaying HTML files, views are provided by the Qt and KDE libraries; we will discuss certain aspects of these high-level widgets in the next section. But for most applications new widgets have to be designed and implemented. It is that what makes a programmer also a designer and where his abilities on creativity are asked. Nevertheless, you should watch for intuitivity first. Remember, a lot of users won't accept an application that isn't:
graphically nice.
offering a lot of features
easy to handle
fast to learn how to use it
Needless to say that stability is a major design goal. Nobody can prevent bugs, but a minimum can be reached at least by clever design goals and wide use of object-oriented design. C++ makes programming a joy if you know how to exploit it's capabilities- inheritance, information hiding and reusablitity of already existing code.
When creating a KDE or Qt project, you always have to have a view that inherits QWidget, either by direct inheritance or because the library widget you want to use inherits QWidget. Therefore, the Application Wizard already constructed a view that is an instance of a class yourappView, which inherits QWidget already.
This chapter therefore describes how to use library widgets for creating views of KDE or Qt applications that are generated with KDevelop, then we look at the libraries and what kind of views are already offered.
