Windows Presentation Foundation

As the name says all, WPF is actually a new framework introduced with .NET framework 3.0 which actually puts forward a new set of classes and assemblies which allows us to write programs more efficiently and flexibly. It uses Direct3D rendering which employs graphics cards to render the output on the screen. Thus the drawing in the form will be smooth and also there is a chance to utilize the hardware capabilities installed in your machine.  In case of traditional GDI forms application,  it is not possible to use advanced graphics capabilities and hence Windows Forms application will always be inefficient in comparison to WPF.  Another important thing that I must address in this regard, GDI Windows forms application uses Operating system controls to build its application. Thus it is basically very hard to customize them in your own application. WPF controls are actually drawn over the screen, and hence you can customize controls totally and modify its behavior when required.

Features of WPF

WPF comes with lots of advantages. Let me introduce you a few of its features :

1. Device Independent Pixel (DPI) :
   WPF introduces Device Independent DPI Settings for the applications built with it. For a window, it is very important to calculate how much Dots Per inch(DPI) the screen could draw. This is generally dependent on the hardware device and operating system in which the application runs and also how the DPI settings is applied on the Device.  Any user can easily customize these settings and hence make the application look horrible. Windows forms application uses pixel based approach so with changing DPI settings, each control will change its size and look.
   
   WPF addresses this issue and makes it independent of DPI settings of the computer. Lets look how its possible :
   
   
   Let say you have drawn a box, just like one in the figure, which is 1 inch long in 96 dpi screen. Now if you see the same application in 120 dpi settings the box will appear smaller. This is because the things that we see on the screen are totally dependent on dpi settings.
   
   In case of WPF, this is modified to density based approach. That means when the density of pixel is modified, the elements will adjust them accordingly and hence the pixel of WPF application is Device Independent Pixel. As you can see in the figure, the size of the control remains same in case of WPF application and it takes more pixel in case of 120 DPI application to adjust the size properly.
   
2. Built-In Support for Graphics and Animation :
   WPF applications as being rendered within DirectX environment, it has major support of graphics and animation capabilities. A separate sets of classes are there which specifically deals with animation effects and graphics. The graphics that you draw over the screen is also Vector based and are object oriented. That means, when you draw a rectangle in WPF application, you can easily remove that from the screen as rectangle is actually an object which you always have hold on. On traditional Windows based application, once you draw a rectangle, you cant select that individually.  Thus programming approach in case of WPF is completely different and more sophisticated than traditional graphics approach. We will discuss graphics and animation in more detail in later section of the article.
   
3. Redefine Styles and Control Templates :
   In addition to graphics and animation capabilities, WPF also comes with a huge flexibility to define the styles and ControlTemplates. Style based technique as you might come across with CSS are a set of definitions which defines how the controls will look like when it is rendered on the screen. In case of traditional windows applications, styles are tightly coupled with each controls, so that you need to define color, style etc for each individual control to make it look differently. In case of WPF, Styles are completely separated from the UIElement. Once you define a style, you can change the look and feel of any control by just putting the style on the element.
   
   Most of the UIElements that we generally deal with is actually made using more than one individual elements. WPF introduces a new concept of Templates, which you might use to redefine the whole control itself. Say for instance, you have a CheckBox, which has a Rectangle in it and a ContentPresenter (one where the caption of the TextBox appears). Thus you can redefine your checkbox and put a ToggleButton inside it, so that the check will appear on the ToggleButton rather than on the Rectangle. This is very interesting. We will look into more detail on Styles and ControlTemplates in later section of the article.
   
4. Resource based Approach for every control:
   Another important feature of WPF is Resource based approach. In case of traditional windows applications, defining styles is very hectic. So if you have 1000 buttons, and you want to apply Color to each Buttons to Gold, you need to create 1000 objects of Color and assign each to one individual elements. Thus it makes it very resource hungry.
   In WPF, you can store styles, controls, animations, and even any object as resource. Thus each resource will be declared once when the form loads itself, and you may associate them to the controls. You can maintain a full hierarchy of styles in separate file called ResourceDictionary, from which styles for the whole application will be applied. Thus WPF application could be themed very easily.
   
5. New Property System & Binding Capabilities:
   
   On the next step, I must introduce the new property system introduced with WPF. Every element of WPF defines a large number of dependency properties. The dependency properties have strong capabilities than the normal properties. Thus when I define our new property, we can easily register my own property to any object I wish to. It will add up to the same observer that is associated to every object. As every element is derived from DependencyObjectin its object hierarchy, each of them contains the Dependency Observer. Once you register a variable as Dependency property, it will create a room on the observer associated with that control and set the value there. We will discuss in more detail in later sections of the series. 

What is XAML ?

According to definition, XAML is an XML based markup language for specifying and setting the characteristics of classes. In other words, XAML is a language used by WPF, silverlight or any other application which can declare classes by itself. So, you can declare a variable, define the properties of any class and directly use it in your application. The XAML parser will automatically parse and create the actual object while it renders the application.
XAML is generally used to define layout of UI, its elements and objects for static and visual aspect. We cannot define flow of a program using XAML. So even though there is large capabilities of XAML, it is actually not a programming language, rather it is used to design UI of the application.  Thus XAML employs other programming languages like C#, VB.NET etc to define the logic in code behind.

ExpressionBuilder is the best tool to generate XAML.

WPF Architecture

For every new technology, it is very essential to have clear idea about its architecture. So before beginning your application you must grab a few concepts. If you dont like to know WPF in detail, please skip this section. As mentioned earlier, WPF is actually a set of assemblies that build up the entire framework. These assemblies can be categorized as

• Managed Layer
• UnManaged Layer
• Core API

Managed Layer : Managed layer of WPF is built using a number of assemblies. These assemblies build up the WPF framework, communicates with lower level unmanaged API to render its content. The few assemblies that comprise the WPF framework are :

1. PresentationFramework.dll : Creates the top level elements like layout panels, controls, windows, styles etc. 
2. PresentationCore.dll : It holds base types such as UIElement, Visual from which all shapes and controls are Derived in PresentationFramework.dll. 
3. WindowsBase.dll : They hold even more basic elements which are capable to be used outside the WPF environment like Dispatcher object, DependencyObjects. I will discuss each of them later. 

Unmanaged Layer (milcore.dll):  The unmanaged layer of WPF is called milcore or Media Integration Library Core. It basically translates the WPF higher level objects like layout panels, buttons, animation etc into textures that Direct3D expects.  It is the main rendering engine of WPF.

WindowsCodecs.dll : This is another low level API which is used for imaging support in WPF applications. WindowsCodecs.dll comprises of a number of codecs which encodes / decodes images into vector graphics that would be rendered into WPF screen.

Direct3D : It is the low level API in which the graphics of WPF is rendered.

User32 : It is the primary core api which every program uses. It actually manages memory and process separation.

GDI & Device Drivers : GDI and Device Drivers are specific to the operating system which is also used from the application to access low level APIs.

In the above figure, you can see how different framework elements communicates between one another that I have just discussed.