[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

This topic contains information about key features and improvements in the .NET Framework 4.5 Developer Preview. This topic does not provide comprehensive information and is subject to change.

New features and improvements are described in the following sections:

- .NET for Metro style apps
- Core New Features and Improvements
- Web
- Networking
- Windows Presentation Foundation (WPF)
- Windows Communication Foundation (WCF)
- Windows Workflow Foundation (WF)

.NET for Metro style apps

Metro style apps are designed for specific form factors and leverage the power of the Windows operating system. A subset of the .NET Framework is available for building Metro style apps for Windows using C# or Visual Basic. This subset is called .NET APIs for Metro style apps.

Core New Features and Improvements

The following features and improvements were added to the common language runtime and to .NET Framework classes:

- Ability to limit how long the regular expression engine will attempt to resolve a regular expression before it times out.
- Ability to define the culture for an application domain.
- Console support for Unicode (UTF-16) encoding.
- Support for versioning of cultural string ordering and comparison data.
- Better performance when retrieving resources.
- Zip compression improvements to reduce the size of a compressed file.
- Ability to customize a reflection context to override default reflection behavior through the CustomReflectionContext class.

Managed Extensibility Framework (MEF)

The Managed Extensibility Framework (MEF) provides the following new features:
- Support for generic types.
- Convention-based programming model that enables you to create parts based on naming conventions rather than attributes.
- Multiple scopes.

Asynchronous File Operations

In the .NET Framework 4.5 Developer Preview, new asynchronous features were added to the C# and Visual Basic languages. These features add a task-based model for performing asynchronous operations. To use this new model, use the asynchronous methods in the I/O classes.


ASP.NET 4.5 Developer Preview includes the following new features:

- Support for new HTML5 form types.
- Support for model binders in Web Forms. These let you bind data controls directly to data-access methods, and automatically convert user input to and from .NET Framework data types.
- Support for unobtrusive JavaScript in client-side validation scripts.
- Improved handling of client script through bundling and minification for improved page performance.
- Integrated encoding routines from the AntiXSS library (previously an external library) to protect from cross-site scripting attacks.
- Support for WebSockets protocol.
- Support for reading and writing HTTP requests and responses asynchronously.
- Support for asynchronous modules and handlers.
- Support for content distribution network (CDN) fallback in the ScriptManager control.


The .NET Framework 4.5 Developer Preview provides a new programming interface for HTTP applications. For more information, see the new System.Net.Http and System.Net.Http.Headers namespaces.

Also, the following networking improvements are included in the System.Net, System.Net.Mail, and related namespaces:

- Improved internationalization and IPv6 support.
- RFC-compliant URI support.
- Support for Internationalized Domain Name (IDN) parsing.
- Support for Email Address Internationalization (EAI).

Windows Presentation Foundation (WPF)

In the .NET Framework 4.5 Developer Preview, Windows Presentation Foundation (WPF) contains changes and improvements in the following areas:

- The new Ribbon control, which enables you to implement a ribbon user interface that hosts a Quick Access Toolbar, Application Menu, and tabs.
- The new INotifyDataErrorInfo interface, which supports synchronous and asynchronous data validation.
- New features for the VirtualizingPanel and Dispatcher classes.
- Improved performance when displaying large sets of grouped data, and by accessing collections on non-UI threads.
- Data binding to static properties, data binding to custom types that implement the ICustomTypeProvider interface, and retrieval of data binding information from a binding expression.
- Repositioning of data as the values change (live shaping).
- Better integration between WPF and Win32 user interface components.
- Ability to check whether the data context for an item container is disconnected.
- Ability to set the amount of time that should elapse between property changes and data source updates.
- Improved support for implementing weak event patterns. Also, events can now accept markup extensions.

Windows Communication Foundation (WCF)

In the .NET Framework 4.5 Developer Preview, the following features have been added to make it simpler to write and maintain Windows Communication Foundation (WCF) applications:

- Simplification of generated configuration files.
- Support for contract-first development.
- Ability to configure ASP.NET compatibility mode more easily.
- Changes in default transport property values to reduce the likelihood that you will have to set them.
- Updates to the XmlDictionaryReaderQuotas class to reduce the likelihood that you will have to manually configure quotas for XML dictionary readers.
- Validation of WCF configuration files by Visual Studio as part of the build process, so you can detect configuration errors before you run your application.
- New asynchronous streaming support.
- New HTTPS protocol mapping to make it easier to expose an endpoint over HTTPS with Internet Information Services (IIS).
- Ability to generate metadata in a single WSDL document by appending ?singleWSDL to the service URL.
- Websockets support to enable true bidirectional communication over ports 80 and 443 with performance characteristics similar to the TCP transport.
- Support for configuring services in code.
- XML Editor tooltips.
- ChannelFactory caching support.
- Binary encoder compression support.

Windows Workflow Foundation (WF)

Several new features have been added to Windows Workflow Foundation (WF) in the .NET Framework 4.5 Developer Preview. These new features include:

- Ability to create state machine workflows.
- Enhanced Workflow Designer features such as the following:
    - Enhanced workflow search capabilities in Visual Studio, including Quick Find and Find in Files.
    - Ability to automatically create a Sequence activity when a second child activity is added to a container activity, and to include both activities in the Sequence activity.
    - Panning support, which enables the visible portion of a workflow to be changed without using the scroll bars.
    - A new Document Outline view that shows the components of a workflow in a tree-style outline view and lets you select a component in the Document Outline view.
    - Ability to add annotations to activities.
    - Ability to define and consume activity delegates by using the workflow designer.
    - Auto-connect and auto-insert for activities and transitions in state machine and flowchart workflows.
- Storage of the view state information for a workflow in a single element in the XAML file, so you can easily locate and edit the view state information.
- A NoPersistScope container activity to prevent child activities from persisting.
- Support for C# expressions:
    - Workflow projects that use Visual Basic will use Visual Basic expressions, and C# workflow projects will use C# expressions.
    - C# workflow projects that were created in Visual Studio 2010 and that have Visual Basic expressions are compatible with C# workflow projects that use C# expressions.
- Versioning enhancements:
    - The new WorkflowIdentity class, which provides a mapping between a persisted workflow instance and its workflow definition.
    - Side-by-side execution of multiple workflow versions in the same host, including WorkflowServiceHost.
    - In Dynamic Update, the ability to modify the definition of a persisted workflow instance.
- Contract-first workflow service development, which provides support for automatically generating activities to match an existing service contract

This article is sourced from http://msdn.microsoft.com/en-us/library/ms171868(v=VS.110).aspx as it is correct as per 19th Sept 2011.