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Working with 3D requires the namespace System.Windows.Media.Medi3D. It provides classes that support 3-D DISPLAY in Windows PRESENTATION Foundation (WPF) APPLICATIONS such as AffineTransform3D, AmbientLight, DiffuseMaterial, ETC.

A to G characters can better explain the need for WPF as follows: 

• A - Executable on any platform (Windows or Web)
• B - SIMPLE binding (no coding required)
• C - STANDARDIZED look and feel (resources, styles, etc.)
• D - Declarative programming (XAML)
• E - Expression Blend animation (Animation easiness)
• F - Hardware acceleration (Fast performance)
• G - Hardware-INDEPENDENT graphics (independent of resolution)

No, there is no substitute for DirectX because cutting-edge games still REQUIRE DirectX. DirectX still offers vastly superior video PERFORMANCE than WPF API. In other words, DirectX will always be preferred over WPF when it comes to game development. Although you can make a game LIKE Tic Tac Toe with WPF, you won't be able to make one with high-action animations. Remember that WPF is designed to replace WindowsForms and not DirectX.

MICROSOFT's WINDOWS Presentation Foundation (WPF) SUPPORTS the following types of documents:  

• Flow format: This format alters the content based on the size of the screen.
• FIXED Format document: A fixed format document presents content REGARDLESS of the size of the screen.

The ability to create custom controls in WPF applications makes it MUCH easier to create flexible and feature-rich controls. You can use custom controls if Microsoft's built-in controls do not meet your requirements or if you do not wish to pay for third-party controls. Basically, a custom control has its own theme, style, and template, which is DEFINED in generic.xaml. There are several scenarios where custom controls are USED:   

• If you need to create the control from SCRATCH since it does not exist.
• If you want to add extra functionality or property to a pre-existing control to meet your specific needs.
• If you need to customize and style your controls.

XAML (Extensible Application Markup Language) is USED by WPF to build user interfaces for Windows applications. XAML files are very powerful, but PARSING them at runtime is rather EXPENSIVE. Therefore, the MarkupCompiler converts XAML into BAML (Binary Application Markup File), which is a more compact binary version. BAML files can be generated from XAML files with the '.BAML’ EXTENSION and embedded into .NET Framework assemblies as resources. BAML is a compressed declarative language that loads and parses FASTER than XAML. 

FREEZABLE objects are special types of objects with two states i.e., unfrozen and frozen. Objects in a frozen state cannot be modified, whereas objects in an unfrozen state can be modified as normal objects. Freezables provide OBSERVERS with a CHANGED event that indicates any modifications to the object. When an object is frozen, it no longer needs to handle change NOTIFICATIONS, which can improve its performance. Freezables can be shared across THREADS when they're frozen, but they can't be shared when they're unfrozen. Brushes, transformations, geometries, pens, and animations are some examples of freezable objects.
Objects in a 'frozen' state cannot be altered anytime. 

Let's consider a brush in a frozen state. What happens when we modify it? 

As shown below, it throws an InvalidOperationException: 

XAML (Extensible Application Markup Language) UI elements can be defined/resolved using the xmlns and xmlns:X NAMESPACES. As the default namespace, xmlns aids in resolving all WPF elements. XAML language definitions are resolved using the xmlns:x namespace. This is prefixed by the “x:” CHARACTER. 

• xmlns Example: 

• xmlns:x Example: 

A good example is the XAML snippet below, in which there are 2 elements - "StackPanel" and "X:name". A "StackPanel" element is resolved using the default namespace and an "x:name" element using the "xmlns:x" namespace. 

GUI ELEMENTS are arranged in an application by layout panels. In the event that you design your controls on fixed coordinates, the application MODEL will not work if you MOVE it to a DIFFERENT ENVIRONMENT with different resolutions. As a result, layout panels are necessary to ensure that your control fits different screen sizes. WPF offers the following layout panels:  

• Stack Panel
• Virtualizing Stack Panel
• Grid Panel
• Canvas Panel
• Dock Panel
• Wrap Panel 

Consequently, these panels are easy to use, versatile, and extensible enough to meet the needs of most applications.

In WPF, triggers are commonly used in Style and Control Templates. The visual effect of a WPF element is changed by triggers when a property or data changes or when an event takes place. The WPF trigger is a very important feature that allows us to MODIFY the visual effect of controls or elements. Therefore, you are able to DYNAMICALLY modify the APPEARANCE and/or behaviour of your control without CREATING a new one. 

Triggers can be divided into three categories:  

• Property Triggers: A change in one property will CAUSE an animated or immediate change in another property.
• Data Triggers: Data triggers are triggered when certain conditions are met by bound data.
• Event Triggers: These triggers take action when a specific event occurs.

In object-oriented design patterns, the command pattern is one of the strongest design patterns. A command pattern refers to a design pattern that uses an object to encapsulate information required for triggering an action or event later. Method name, an object that owns the method, and the parameters of the method are among the information included here. In situations where you NEED to execute operations BASED on user requests, the command pattern is the best approach to MANAGE objects.

WPF's command design pattern consists of the following members:

• CLIENT: Creates a command object and SETS its receiver.
• Invoker: Request command object to perform an action.
• Command: Defines the Execute operation.
• Concreate Command: Invokes the Execute operation on the receiver.
• Receiver: Executes the action requested.

In WPF, a mechanism called DataBinding allows data to be automatically UPDATED between BUSINESS models and user interfaces. Data binding enables WPF applications to PRESENT and access data in a consistent and simple way. In data binding, a connection is established between the application UI (User Interface) and the data that the application displays. When a binding is established, changes to data in the business model are automatically reflected in the UI elements that are bound to it and vice VERSA. In WPF, this is the most preferred method of getting data to the user interface. 

Source properties of a data binding can be either normal .NET properties or DependencyProperties, but target properties must always be DependencyProperties.  

Resources can be classified into two types:  

• Static Resource: Resources with this type are only evaluated once at the time of XAML loading. Resources that are static are evaluated only once, and if they change after that, those CHANGES aren't reflected in the binding. They can't be modified at runtime and REMAINS the same (static) throughout the life of the application.
• Dynamic Resource: This is a resource that we use when we need to change the value of a property during execution. It is evaluated each time the resource is needed. When you change the CODE behind a resource, the elements that refer to it as a dynamic resource will ALSO change.

Example: If you implement "bitmapImageResource" as a static resource, it will remain the same, even if the source of the image is CHANGED. However, if you use "textForeColorResource" as a dynamic resource and change its color at runtime, then any element which references this resource will be affected. 

In WPF, a resource is a type of object that you can reuse across multiple PLACES. The resource concept provides a simple way for objects and values to be reused. For instance, you can use resources such as styles, BRUSHES, bitmap images, etc., in various places within your WPF application. A unique key is assigned to each resource so it can be referenced from other parts of the application. The WPF resources allow you to set properties of several controls at once. The background property can be set for multiple elements in a WPF application using a single resource, for example.  Resources can be DECLARED at:

• WPF Resource declaration can be done at the application LEVEL in App.xaml.
• In addition, WPF Resources can be declared at the Window/User Control level or at the Panel level.
• In the event that your resource PROVISIONING needs grow, then you can declare them in a separate file called a Resource Dictionary that you can refer to at the application level or any other level you desire.

You can CHANGE the alignment of text in text boxes and buttons using content alignment. The content of content CONTROLS can be controlled by a number of properties in WPF. TWO of these properties are:  

• HorizontalContentAlignment
• VerticalContentAlignment

System.Windows.Controls.Control, the parent class for all WPF controls, defines these properties. 

Example: 

Suppose you want to create a UI (User Interface) with a Button and TextBox. The default vertical/horizontal alignment of a button's content is center, while the default vertical/horizontal alignment of a TextBox is top and left, as shown below. 

But what if you want TextBoxes and Button contents positioned differently? Let's say you want to PLACE the content of the Button and TextBox right and bottom, respectively. 

VerticalContentAlignment and HorizontalContentAlignment properties are set to bottom and right, respectively, in the following code. 

It produces output similar to that shown below. You can see that the content in the TextBox and Button are aligned to the right and bottom, respectively. 

The following are a few important FEATURES of WPF: 

• It USES XAML (Extensible Application Markup Language) to build user interfaces for Windows applications. It allows visual designers to create UI (User Interface) elements, data binding, and events.
• WPF includes user controls such as sliders, checkboxes, and buttons necessary for developing DESKTOP client applications.
• Furthermore, it OFFERS data binding capabilities and supports multimedia integration.
• WPF provides an easy-to-use graphical display system for Windows.
• You can create your own custom UI controls with unlimited possibilities and flexibility.
• A variety of animations and special effects can be added to the controls and UI elements on the screen.
• A flow document model is supported which allows "desktop publishing" layout features.
• Smooth graphical effects, like color gradients and drop shadows, are possible.
• It uses hardware acceleration for rendering GUI (Graphical User Interface) to improve performance.
• The WPF applications are screen resolution-independent so you can create WPF applications that support a variety of screen resolutions.