|Initial release||November 21, 2006|
v6.0.2 / February 9, 2022
|Written in||C#, C++, C|
|Operating system||Microsoft Windows|
|Platform||.NET Framework, .NET|
Windows Presentation Foundation (WPF) is a free and open-source graphical subsystem (similar to WinForms) originally developed by Microsoft for rendering user interfaces in Windows-based applications. WPF, previously known as "Avalon", was initially released as part of .NET Framework 3.0 in 2006. WPF uses DirectX and attempts to provide a consistent programming model for building applications. It separates the user interface from business logic, and resembles similar XML-oriented object models, such as those implemented in XUL and SVG.
WPF employs XAML, an XML-based language, to define and link various interface elements. WPF applications can be deployed as standalone desktop programs or hosted as an embedded object in a website. WPF aims to unify a number of common user interface elements, such as 2D/3D rendering, fixed and adaptive documents, typography, vector graphics, runtime animation, and pre-rendered media. These elements can then be linked and manipulated based on various events, user interactions, and data bindings.
WPF runtime libraries are included with all versions of Microsoft Windows since Windows Vista and Windows Server 2008. Users of Windows XP SP2/SP3 and Windows Server 2003 can optionally install the necessary libraries.
Microsoft Silverlight provided functionality that is mostly a subset of WPF to provide embedded web controls comparable to Adobe Flash. 3D runtime rendering had been supported in Silverlight since Silverlight 5.
At the Microsoft Connect event on December 4, 2018, Microsoft announced releasing WPF as open source project on GitHub. It is released under the MIT License. Windows Presentation Foundation has become available for projects targeting the .NET software framework, however, the system is not cross-platform and is still available only on Windows.
Graphics, including desktop items like windows, are rendered using Direct3D. This allows the display of more complex graphics and custom themes, at the cost of GDI's wider range of support and uniform control theming. It allows Windows to offload some graphics tasks to the GPU. This reduces the workload on the computer's CPU. GPUs are optimized for parallel pixel computations. This tends to speed up screen refreshes at the cost of decreased compatibility in markets where GPUs are not necessarily as powerful, such as the netbook market.
WPF's emphasis on vector graphics allows most controls and elements to be scaled without loss in quality or pixelization, thus increasing accessibility. With the exception of Silverlight, Direct3D integration allows for streamlined 3D rendering. In addition, interactive 2D content can be overlaid on 3D surfaces natively.
DocumentViewerclass, which is for reading fixed layout documents. The
FlowDocumentReaderclass offers different view modes such as per-page or scrollable and also reflows text if the viewing area is resized.
To enable the use of WinForms, the developer executes this from their WPF C# code:
Main article: Extensible Application Markup Language
Following the success of markup languages for web development, WPF introduces eXtensible Application Markup Language (XAML; /ˈzæməl/), which is based on XML. XAML is designed as a more efficient method of developing application user interfaces. The specific advantage that XAML brings to WPF is that XAML is a completely declarative language, allowing the developer (or designer) to describe the behavior and integration of components without the use of procedural programming. Although it is rare that an entire application will be built completely in XAML, the introduction of XAML allows application designers to more effectively contribute to the application development cycle. Using XAML to develop user interfaces also allows for separation of model and view, which is considered a good architectural principle. In XAML, elements and attributes map to classes and properties in the underlying APIs.
As in web development, both layouts and specific themes are well suited to markup, but XAML is not required for either. Indeed, all elements of WPF may be coded in a .NET language (C#, VB.NET). The XAML code can ultimately be compiled into a managed assembly in the same way all .NET languages are.
The architecture of WPF spans both managed code and native code components. However, the public API exposed is only available via managed code. While the majority of WPF is in managed code, the composition engine which renders the WPF applications is a native component. It is named Media Integration Layer (MIL) and resides in
milcore.dll. It interfaces directly with DirectX and provides basic support for 2D and 3D surfaces, timer-controlled manipulation of contents of a surface with a view to exposing animation constructs at a higher level, and compositing the individual elements of a WPF application into a final 3D "scene" that represents the UI of the application and renders it to the screen. The Desktop Window Manager also uses the MIL for desktop and window composition. The media codecs are also implemented in unmanaged code, and are shipped as
windowscodecs.dll. In the managed world, PresentationCore (
presentationcore.dll) provides a managed wrapper for MIL and implements the core services for WPF, including a property system that is aware of the dependencies between the setters and consumers of the property, a message dispatching system by means of a
Dispatcher object to implement a specialized event system and services which can implement a layout system such as measurement for UI elements. PresentationFramework (
presentationframework.dll) implements the end-user presentational features, including layouts, time-dependent, story-board based animations, and data binding.
WPF exposes a property system for objects which inherit from
DependencyObject, that is aware of the dependencies between the consumers of the property, and can trigger actions based on changes in properties. Properties can be either hard coded values or expressions, which are specific expressions that evaluate to a result. In the initial release, however, the set of expressions supported is closed. The value of the properties can be inherited from parent objects as well. WPF properties support change notifications, which invoke bound behaviors whenever some property of some element is changed. Custom behaviors can be used to propagate a property change notification across a set of WPF objects. This is used by the layout system to trigger a recalculation of the layout on property-changes, thus exposing a declarative programming style for WPF, whereby almost everything, from setting colors and positions to animating elements can be achieved by setting properties. This allows WPF applications to be written in XAML, which is a declarative mark-up language, by binding the keywords and attributes directly to WPF classes and properties.
The interface elements of a WPF application are maintained as a class of
Visual objects. Visual objects provide a managed interface to a composition tree which is maintained by Media Integration Layer (MIL). Each element of WPF creates and adds one or more composition nodes to the tree. The composition nodes contain rendering instructions, such as clipping and transformation instructions, along with other visual attributes. Thus the entire application is represented as a collection of composition nodes, which are stored in a buffer in the system memory. Periodically, MIL walks the tree and executes the rendering instructions in each node, thus compositing each element on to a DirectX surface, which is then rendered on screen. MIL uses the painter's algorithm, where all the components are rendered from back of the screen to the front, which allows complex effects like transparencies to be easily achieved. This rendering process is hardware accelerated using the GPU. The composition tree is cached by MIL, creating a retained mode graphics, so that any changes to the composition tree needs only to be incrementally communicated to MIL. This also frees the applications of managing repainting the screen; MIL can do that itself as it has all the information necessary. Animations can be implemented as time-triggered changes to the composition tree. On the user visible side, animations are specified declaratively, by setting some animation effect to some element via a property and specifying the duration. The code-behind updates the specific nodes of the tree, via
Visual objects, to represent both the intermediate states at specified time intervals as well as the final state of the element. MIL will render the changes to the element automatically.
All WPF applications start with two threads: one for managing the UI and another background thread for handling rendering and repainting. Rendering and repainting is managed by WPF itself, without any developer intervention. The UI thread houses the Dispatcher (via an instance of
DispatcherObject), which maintains a queue of UI operations that need to be performed (as a tree of
Visual objects), sorted by priority. UI events, including changing a property that affects the layout, and user interaction events raised are queued up in the dispatcher, which invokes the handlers for the events. Microsoft recommends that the event handlers only update the properties to reflect new content for application responsiveness, with the new content being generated or retrieved in a background thread. The render thread picks up a copy of the visual tree and walks the tree calculating which components will be visible and renders them to Direct3D surfaces. The render thread also caches the visual tree, so only changes to the tree need to be communicated, which will result in updating just the changed pixels. WPF supports an extensible layout model. Layout is divided into two phases: Measure; and Arrange. The Measure phase recursively calls all elements and determines the size they will take. In the Arrange phase, the child elements are recursively arranged by their parents, invoking the layout algorithm of the layout module in use.
A number of development tools are available for developing Windows Presentation Foundation applications.
WPF's deployment model offers both standalone and XAML Browser Applications (XBAP, pronounced "ex-bap") flavors. The programming model for building either type of application is similar.
Standalone applications are those that have been locally installed on the computer using software such as ClickOnce or Windows Installer (MSI) and which run on the desktop. Standalone applications are considered full trust and have full access to a computer's resources.
XAML Browser Applications (XBAPs) are programs that are hosted inside a web browser. Pre-.NET4 XBAP applications run in a partial trust sandbox environment, and are not given full access to the computer's resources and not all WPF functionality is available. The hosted environment is intended to protect the computer from malicious applications. XBAPs can run as fully trusted applications in .NET 4, with full access to computer resources. Starting an XBAP from an HTML page or vice versa is seamless (there is no security or installation prompt). Although one gets the perception of the application running in the browser, it actually runs in an out-of-process executable different from the browser.
As of the release of .NET Framework 3.0, XBAPs would only run in IE.
With the release of .NET Framework 3.5 SP1, XBAP also runs in Mozilla Firefox using the included extension. On October 16, 2009, Mozilla added the Firefox plugin and extension to its add-ons blocklist, because of a remotely exploitable serious security vulnerability, in agreement with Microsoft. Two days later, the block was removed. On Windows 7, the Firefox plugin does not run by default. A reinstallation of the .NET Framework 3.5 SP1 will install the plugin and add support for XBAP applications on Firefox. Alternatively, hard-copying the plugin DLLs from a working Windows XP/Vista installation to the plugin directory of Mozilla Firefox will also reinstate support for XBAP applications. The WPF plugin DLLs reside in the following directories (depending on the Framework version):
Main article: Microsoft Silverlight
Silverlight (codenamed WPF/E) is a deprecated cross-browser browser plugin which contained WPF-based technology (including XAML) that provided features such as video, vector graphics, and animations to multiple operating systems including Windows 7, Windows Vista, Windows XP, and Mac OS X. Microsoft sanctioned a limited number of third-party developers to work on ports for certain Linux distributions. Specifically, it was provided as an add-on for Mozilla Firefox, Internet Explorer 6 and above, Google Chrome 42 and below and Apple Safari.
The .NET Micro Framework includes a GUI object model loosely based on WPF, although without support for XAML.