Windows Presentation Foundation (WPF)

1. To keep up with increasing expectations of users, the technology used to create user interfaces must also advance.
   
   The goal of Windows Presentation Foundation (WPF) is to provide these advances for Windows. Included in version 3.0 of the Microsoft .NET Framework, WPF allows building interfaces that incorporate documents, media, two- and three-dimensional graphics, animations, Web-like characteristics, and much more.
   
   A Unified Platform for Modern User Interfaces
   In a pre-WPF world, creating a Windows user interface like the one described earlier would require using several different technologies. The table below summarizes the situation.
   
   ~Table~
   
   The Ability for Developers and Designers to Work Together
   The way the two disciplines interact today is problematic. Most commonly, a designer uses a graphical tool to create static images of the screen layouts that an application should display. He then gives these images to the developer, whose job is to create the code that makes them real. Something that's easy for a designer to draw, however, might be difficult or impossible for a developer to implement. Technology limitations, schedule pressures, lack of skill, misunderstandings, or simple disagreement might prevent the developer from fully realizing the designer's vision. What's needed is a better way for members of these two interdependent disciplines to work together without compromising the quality of the interface.
   To allow this, WPF introduces the eXtensible Application Markup Language (XAML). XAML defines a set of XML elements such as Button, TextBox, Label, and many more to define exactly how a user interface looks. XAML elements typically have attributes as well, allowing various options to be set. For example, this simple XAML snippet creates a red button containing the word "No":
   
   
   
   A Common Technology for Windows and Web Browser User Interfaces
   
   Creating effective user interfaces for Windows applications is important. Yet creating effective interfaces for Web-based applications is at least as important. By definition, these interfaces are provided by a Web browser, and the simplest approach is just to let the browser passively display whatever HTML it receives. More responsive browser interfaces provide logic running in JavaScript, perhaps using asynchronous JavaScript and XML (AJAX). The interface may even support animations, video, and more using Adobe's Flash Player or some other technology. Sometimes known as rich Internet applications, Web software that provides this kind of full-featured interface can significantly improve the user's experience. It can also add substantial business value by making a Web application more attractive to users.
   
   The Technology of Windows Presentation Foundation
   
   Application Model
   At its root, every application inherits from WPF's standard Application class. This class provides common services that are useful to every application. These include holding state that needs to be available to the entire application and providing standard methods such as Run, which starts the application, and Shutdown, which terminates it.
   
   
   An Application object can be created with either XAML, via the Application element, or code, using the Application class. (This is true for virtually everything in WPF, but for simplicity, this paper always uses the XAML option.) Here's a simple XAML illustration
   
   . . .
   
   Layout and Controls
   Like any user interface technology, WPF provides a large set of controls, and developers are free to create custom controls as well. The standard set includes Button, Label, TextBox, ListBox, Menu, Slider, and other traditional atoms of user interface design. More complex controls are also provided, such as SpellCheck, PasswordBox, controls for working with ink (as with a Tablet PC), and more.
   
   As usual in a graphical interface, events generated by the user, such as mouse movements and key presses, can be caught and handled by the controls in a WPF application. While controls and other user interface elements can be fully specified using XAML, events must be handled in code. For example, here's a XAML definition of a simple Button on a Canvas:
   
   
   
   and the code
   
   namespace Example {
   public partial class CodeForCanvas : Canvas {
   void Button_Click(object sender, RoutedEventArgs e) {
   Button btn = e.Source as Button;
   btn.Background = Brushes.Purple;
   }
   }
   }
   
   The namespace and class name match that specified in the Canvas tag just shown. The class CodeForCanvas inherits from the base Canvas class provided by WPF, and it's defined as a partial class. Partial classes were a new addition in version 2.0 of the .NET Framework, and they allow combining code defined separately into a single class. In this case, the XAML-defined Canvas generates a partial class that gets combined with the partial class shown here. The result is a complete class capable of both displaying a canvas with a button and handling its event.
   
   
   Styles and Templates
   Using XAML's Style element, the creator of a WPF application can define one or more aspects of how something should look, then apply that style over and over. For example, a style named ButtonStyle might be defined like this:
   
   
   
   Any Button defined using this style would be given a red background and use a font size of 16. For example:
   
   
   
   Other Technologies are
   
   Text
   Documents
   Images
   Video and Audio
   Two-Dimensional Graphics
   Three-Dimensional Graphics
   Transformation and Effects
   Animation
   User Interface Automation