MEF in .NET 4.0/Visual Studio 2010 – Simple Example

The Managed Extensibility Framework (MEF) is a new library in .NET Framework 4.0 that helps in simplifying the design of extensible applications and components. If you are developing a .NET application (WinForms, WPF, Silverlight or ASP.Net) that supports plugins (independent libraries with different functionalities), then MEF is very handy.

Let us examine the basics of MEF through a very plain example application. I am building a WinForms showroom application which will display different vehicles. I have my own vehicles to display, and the application also supports vehicles from other vendors (aka plugins). All they need to do is to stick to my contract (aka implement the interface I give) while they develop their vehicles.

Let us first define the required contract. In Visual Studio 2010 (My version is Beta 2), create a new C# class library project and name it as Showroom.Contracts. Add an interface to it as below:

namespace Showroom.Contracts
{
    public interface IVehicle
    {
        string GetVehicleDetails();
    }
}

Now let us assume that we distribute this contract (interface library) to other vendors so that they can create vehicles that will fit in our showroom. To portray this scenario add another class library project named Vehicle.Hyundai. Add Showroom.Contracts project as a reference to this project as we need to implement the contract interface. This is going to be a plugin (extension or ComposablePart in MEF terminology) and hence we need to also add a reference to the MEF library System.ComponentModel.Composition. Add a class as shown below to this project:

namespace Vehicle.Hyundai
{
    using System.ComponentModel.Composition;
    using Showroom.Contracts;

    [Export(typeof(IVehicle))]
    public class HyundaiSonata : IVehicle
    {
        string IVehicle.GetVehicleDetails()
        {
            return "Hyundai Sonata";
        }
    }
}

Notice the Export attribute. This informs MEF that this is a plugin of type IVehicle. Now let us add one more similar class:

namespace Vehicle.Hyundai
{
    using System.ComponentModel.Composition;
    using Showroom.Contracts;

    [Export(typeof(IVehicle))]
    public class HyundaiSantro : IVehicle
    {
        string IVehicle.GetVehicleDetails()
        {
            return "Hyundai Santro!";
        }
    }
}

To portray one more vendor, add another class library project named Vehicle.Maruti and add a similar class to this as well:

namespace Vehicle.Maruti
{
    using System.ComponentModel.Composition;
    using Showroom.Contracts;

    [Export(typeof(IVehicle))]
    public class MarutiSwift : IVehicle
    {
        string IVehicle.GetVehicleDetails()
        {
            return "Maruti Swift";
        }
    }
}

Now that the contract and plugins based on these contracts are ready, let us build the showroom host or shell application to display these vehicles. Add a new WinForms project to the solution named Showroom.Shell. Add a project reference to Showroom.Contracts and reference to System.ComponentModel.Composition. Add a listbox to the form and name it as uxVehicles. This will display all the vehicles we have.

Remember we have our own vehicles to display in the showroom (besides vehicles from other vendors). Let us add a new class to the project:

namespace Showroom.Shell
{
    using System.ComponentModel.Composition;
    using Showroom.Contracts;

    [Export(typeof(IVehicle))]
    public class ShowroomVehicle1: IVehicle
    {
        string IVehicle.GetVehicleDetails()
        {
            return "Showroom Vehicle Normal";
        }
    }
}

And one more similar one:

namespace Showroom.Shell
{
    using System.ComponentModel.Composition;
    using Showroom.Contracts;

    [Export(typeof(IVehicle))]
    public class ShowroomVehicle2 : IVehicle
    {
        string IVehicle.GetVehicleDetails()
        {
            return "Showroom Vehicle Special";
        }
    }
}

Note that these are also decorated with Export attribute for MEF to pick them up later. Now go to the source code of Form1 to build the shell logic:

namespace Showroom.Shell
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.Composition;
    using System.ComponentModel.Composition.Hosting;
    using System.Reflection;
    using System.Windows.Forms;
    using Showroom.Contracts;

    public partial class Form1 : Form
    {
        [ImportMany(typeof(IVehicle))]
        public List<IVehicle> Vehicles { get; set; }

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            this.Vehicles = new List<IVehicle>();

            AggregateCatalog cat = new AggregateCatalog();
            cat.Catalogs.Add(new AssemblyCatalog(Assembly.GetExecutingAssembly()));
            cat.Catalogs.Add(new DirectoryCatalog("Plugins"));

            CompositionContainer contnr = new CompositionContainer(cat);

            contnr.ComposeParts(this);

            foreach (IVehicle item in this.Vehicles)
            {
                uxVehicles.Items.Add(item.GetVehicleDetails());
            }
        }
    }
}

We have declared a property named Vehicles to contain all the vehicles we plan to display in our showroom. Notice the ‘ImportMany’ attribute. It tells MEF that this property need to be loaded using plugins of type ‘IVehicle’. We have used ‘ImportMany’ as there are more than one vehicle and will be using ‘Import’ instead if there is only one plugin.

MEF's core is comprised of a catalog and a CompositionContainer. A catalog is responsible for discovering extensions (plugins) and the container coordinates creation and satisfies dependencies. The AssemblyCatalog gathers plugins from an assembly. Here we have asked it to find all the plugins (classes with ‘Export’ attributes) from the currently executing assembly (Showroom.Shell). The DirectoryCatalog gathers plugins from a directory. Here we have asked the catalog to look in a directory named ‘Plugins’ for the assemblies containing classes that have ‘Export’ attribute. We have used AggregateCatalog to aggregate the tow different (Assembly and Directory) catalogs of plugins into one. The ComposeParts method of the CompositionContainer does all the magic by importing the required types from these plugins and loading them to the corresponding properties. Here in our code, the property ‘Vehicles’ will now be loaded with all the available vehicle plugins and we call their ‘GetVehicleDetails’ methods to add the results to a the listbox.


Before running this application, copy the plugin assemblies (Vehicle.Hyundai.dll and Vehicle.Maruti.dll) to a folder named ‘Plugins’ under ..\bin\Debug\ folder of the Showroom.Shell project.

Download the complete sample (works in Visual Studio 2010 Beta 2) from here http://wayfarer.bizhat.com/techbites/downloads/mef_showroom1.zip

Visual Studio 2010 and .NET 4.0 Features

I started working in Visual Studio since its early Visual Basic days. The latest in that series was 6.0.  Then came a series of .NET platform versions: Visual Studio .NET (Rainier, 2003-Feb),  Visual Studio .NET 2003 (Everett, 2003-Apr), Visual Studio 2005 (Whidbey, 2005-Oct) and Visual Studio 2008 (Orcas, 2007-Nov). The latest version of Microsoft Visual Studio is VS 2010 (Code Name: Hawaii) and is expected to be available for public in March, 2010. I tried out the recently released Beta 2 version of VS 2010 and its cool.


Here are some of the new features (collected from various blogs including ScottGu's Blog and Kevin McNeish's Blog):
Visual Studio

• Fresh look and feel with a blue based new logo and color theme.
• Works side by side with VS 2008 and supports Multi Targeting (.NET 2.0, 3.0, ...).
• New Product Lineup (Express, Professional, Premium, Ultimate).
• Multi-Monitor Support (editors, designers and tool-windows).
• Silverlight UI layout support.
• Data binding support for both WPF and Silverlight.
• Zoom in/out of any code editing window or text editing window.
• Call hierarchy for C# is available at design time (Similar to stack trace; Right click on a symbol(method or class, etc.) and choose View Call Hierarchy).
• Naviagate To (Edit > Navigate To or Ctrl+Comma) option to do quick search for a symbol or file in the source code (can search part of a name or abbreviation like IC for InitializeComponent, and can specify multiple strings separated by space).
• Highlight References: Put the cursor on a symbol and after a short delay, all its references are highlighted. Or use Find all references (Right click on a symbol and choose Find All References) to see all its instances.(Ctrl-Shift-up/down arrow to cycle)
• Consume First Development: Even if there is no class by name Person, you can type Person obj = new Person(); and then choose to generate the class. (Ctrl+ Dot)
• Tools > Extension Manager to manage add-ins.

.NET Framework 4.0

• Dynamic Language Support. [kind of late binding: dynamic Car = GetCar();]
• MEF (Managed Extensibility Framework) for developing applications that supports plugins.
• Optional Parameters [Supply a default value to make it optional: public void CreateBook(string title="No Title", string isbn = "0-00000-000-0"){}]
• Named Parameters [Supply parameter values in any order specifying its name: CreateBook(isbn: "5-55555-5555-5"); or CreateBook("Book Title", isbn: "5-55555-5555-5");]
• Co-variance and Contra-variance support [IEnumerable<string> strings = GetStrings();IEnumerable<object> objects = strings; is now possible.]

ASP.NET 4.0

• Starter Project Templates (Installed & Online; Empty, Normal, MVC, Ajax, etc.).
• Clean Web.Config Files.
• Code Optimized Web Development Profile(Or Tools>Options>HTML Designer>Off Designer)
• ASP.NET, HTML, JavaScript Snippet Support.
• Auto start: Only on IIS 7.5 (well-defined approach to perform expensive application startup).
• URL Routing with ASP.NET 4 Web Forms.

WPF 4.0

• New controls: DataGrid, DatePicker, and Calendar
• Bag O’ Tricks controls: AnimatingTilePanel, ColorPicker, InfoTextBox, ListPager, NumericUpDown, Reveal, TransitionsPresenter, TreeMapPanel.
• Extra control: Windows 7 & Office Ribbon Control
• Graphics improvements: Cached Composition, Pixel Shader 3 Support, LayoutRounding, Animation Easing Function, CleartypeHint
• Text improvements: New Text Rendering Stack, Display-optimized character layout, explicitly selecting aliased, grayscale, or ClearType rendering modes, optimizing text hinting and snapping, support for fonts with embedded bitmaps, BindableRun (Run.Text), Custom Dictionaries, Selection and Caret Brush
• Windows 7 Multitouch Support: Multi-touch Manipulation, Inertia (Pan, Zoom, Rotate) events on UIElement, Raw multi-touch events (Up, Move, Down) on UIElement, UIElement3D and ContentElement, Multiple capture supporting multiple active controls, ScrollViewer enhancement to support multi-touch panning, Touch device extensibility, Future Surface SDK compatibility
• Windows 7 Shell Integration: Jump List (Tasks, Items, Recent and Frequent Lists) and Taskbar (Progress bar, Overlay Icon, Thumbnail buttons with commanding support, Description Text) integration
• Fundamentals: New XAML/BAML Parser Engine, Data Binding Support for DLR, Visual State Manager (VSM), HTML-XBAP Script Interop, UIAutomation Virtualization, SynchronizedInput Pattern
• Deployment: .NET Framework 4 Client Profile, Full Trust XBAP Deployment

Win Forms 4.0

• No new features or controls!
• Will maintain compatibility for applications already written in WinForms.
• Bug fixes and perf improvements.

WiX - Windows Installer XML

Windows Installer

The Windows Installer is an engine for the installation, maintenance, and removal of software on modern Microsoft Windows systems. The installation information, and often the files themselves, are packaged in installation packages, commonly known as "MSI files", from their default file extension.
Windows Installer is positioned as an alternative to stand-alone executable installer frameworks such as NSIS, and older versions of InstallShield and Wise.
MSI packages can be created using Visual Studio through a Setup project or using third party tools like InstallShield, Wise Installer and WiX.

Windows Installer XML

The Windows Installer XML (WiX, pronounced "wicks"), is a free software toolset that builds Windows Installer (MSI) packages from an XML document. It supports both command-line environment and integrated Visual Studio environment.
The WiX distribution includes Votive, a Visual Studio add-in that allows creating and building WiX setup projects using the Visual Studio IDE. Votive supports syntax highlighting and IntelliSense for .WXS source files and adds a WiX setup project type to Visual Studio.

WiX Download

WiX can be downloaded from http://sourceforge.net/projects/wix/files/. The latest version is 3.0 and the downloaded zip file (wix3.0.5419.0-x86-setup.zip) will contain Wix3.msi. Double click on this after closing all the Visual Studio instances. This will install all the required Wix tools (there are a lot of them and they have interesting names all associated to the wicks of a candle) to %PROGRAMFILES%\ \Windows Installer XML v3\ and the required Visual Studio add-in and project templates.
The bin sub folder under this contains all the tools like candle.exe (compiler and that convert source code into object files), light.exe (linker that take multiple object files and resources to create final setup package), and other tools like dark, light, heat, smoke, torch, etc. The doc sub folder has a detailed help file by name Wix.chm. A detailed tutorial is available at http://wix.sourceforge.net/manual-wix3/main.htm.

Visual Studio WiX Project

First create a sample application to test the WiX. I created a simple Windows Application project. Now add a new WiX Project to the solution (Project Type: WiX, Template: WiX Project) and name it as SampleApp.Setup.
The project will have a default ‘Product.wxs’ file containing the WiX source code to create an MSI package. The WiX source code is nothing but a set of XML tags. Remove the commented tags in the default file and add application exe as shown below:

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
  <Product Id="b464316e-5c06-4cae-be36-0748d51ceb03"
           Name="SampleApp.Setup"
           Language="1033"
           Version="1.0.0.0"
           Manufacturer="SampleApp.Setup"
           UpgradeCode="e0ad76e3-7ad8-436f-b3cd-9f30fcabb1d9">
    <Package InstallerVersion="200"
             Compressed="yes" />

    <Media Id="1"
           Cabinet="media1.cab"
           EmbedCab="yes" />

    <Directory Id="TARGETDIR"
               Name="SourceDir">
      <Directory Id="ProgramFilesFolder">
        <Directory Id="INSTALLLOCATION"
                   Name="SampleApp.Setup">
          <Component Id="ProductComponent"
                     Guid="9102229d-8f5c-474d-be69-00085b3230a2">
            <File Id="SampleApp.exe"
                  Name="SampleApp.exe"
                  Source="$(var.SolutionDir)\SampleApp\$(var.OutDir)SampleApp.exe"
                  KeyPath="yes"
                  Checksum="yes"/>
          </Component>
        </Directory>
      </Directory>
    </Directory>

    <Feature Id="ProductFeature"
             Title="SampleApp.Setup"
             Level="1">
      <ComponentRef Id="ProductComponent" />
    </Feature>
  </Product>
</Wix>

Let us now inspect each elements of this file:
WiX: Root element of a WiX installer.
Product: An msi will always contain a single product which is the software we are planning to install. It requires a unique GUID and we can specify other properties like product name, version and manufacturer.
Package: Used to set the packaging properties. Basically we say compression is needed or not.
Media: Describes the installation media for the installer. By default it is a cabinet file named media1.cab which is embedded within the msi file. All the other files will be compressed to this cab file.
Directory: Now we need to specify a group of directory structure that we plan to build on the target machine. All these directories should be within the virtual TARGETDIR directory. In this case, we have the root folder as ‘ProgramFilesFolder’ which is the keyword for system folder ‘%PROGRAMFILES%\’ which will be typically to ‘C:\Program Files\’. Inside this directory we are creating another directory named ‘SampleApp.Setup’. So our final destination folder will be ‘C:\Program Files\SampleApp.Setup\’.
Component: The component is the atomic unit of things to be installed. It consists of resources—files, registry keys, shortcuts or anything else—that should always be installed as a single unit.
File: This represents a file that we need to copy to the target system. Here we are specifying the output exe of our simple application. Note that ‘$(var.SolutionDir)’ is a preprocessor variable that will point to the actual solution directory. Same way, ‘$(var.OutDir)’ represents the project output directory (bin\Debug or bin\Release).
Feature: Features are separated parts of the application that we offer the user to decide whether to install or not. Examples are core files, samples, documentation, etc. Here we have just single feature which is our lone app exe referred by Component Id.
Building this project will create an msi named SampleApp.Setup.msi at the bin\Debug folder of the setup project.
This is the very basic installer without any user interaction options, and it will just show a progress bar of the installation. After completion, you can see that SampleApp .exe is copied to C:\Program Files\SampleApp.Setup\ folder. There are no start menu items or shortcuts created, but there will be an entry in Add or Remove programs list (Programs and Features) from where you can uninstall this program.

WiX User Interface

Adding a standard user interface to the installer is very easy with WiX. First add a reference to WixUIExtension.dll (available in’ %PROGRAMFILES%\ Windows Installer XML v3\bin\’ folder) in the setup project. Now add the following line just above the Product closing tag.

<UIRef Id="WixUI_Minimal"/>

UIRef tells WiX which UI style should be used and we have chosen the ‘Minimal’ with basic options. That’s it. Now build the project and run the installer. It will have a default user interface with license page, progress page and a finish page.
If you re-run the installer after installing it once, the UI will change to provide a ‘Repair’ or ‘Remove’ option. ‘Remove’ can be used to uninstall the program.
Providing the user with an option to choose the installation directory is also very easy. Instead of the UIRef element used above, add the following two lines:

<Property Id="WIXUI_INSTALLDIR"
              Value="INSTALLLOCATION" />
<UIRef Id="WixUI_InstallDir"/>

Here we have chosen the ‘InstallDir’ UI style and the selected directory is assigned to the ‘INSTALLLOCATION’ value which we are referring within the directory structure. Now when you run this new installer, the user will have an option to choose the installation directory.
Other UIRef include WixUI_FeatureTree (allows features to be selected) and WixUI_Mondo (provides typical, custom and complete install options).

WiX User Interface Customization

You can customize some visual aspects of the user interface by simply providing replacement files. To add your own license file for example, add a license rtf file to the setup project and then add the below line just above Produc> closing tag:

<WixVariable Id="WixUILicenseRtf" Value="license.rtf" />

Other such options are:

<WixVariable Id="WixUIBannerBmp" Value="mybanner.bmp" />
<WixVariable Id="WixUIDialogBmp" Value="mydialog.bmp" />

Dialog is the first install page’s background image (493 x 312 pixels bmp) and Banner is the top banner image on subsequent pages (493 x 58 pixels bmp).
Download a complete Visual Studio 2008 Solution with sample WiX project from here: wixsample.zip. And here is the complete WiX code for that:

<?xml version="1.0" encoding="UTF-8"?>
<!--Author: Sameer C Thiruthikad | Last Modified: 2009-Oct-16-->
<!--Defining some constants-->
<?define Property_ProductName = "My Sample App" ?>
<?define Property_Manufacturer = "My Company" ?>

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
  <Product Name='$(var.Property_ProductName)'
           Id='{C24FBDCE-AD5D-4f0d-AD4B-9E75EB78D231}'
           UpgradeCode='{DCE43671-9C09-4fb0-AC05-34D4AF71563E}'
           Language='1033'
           Codepage='1252'
           Version='1.0.0'
           Manufacturer='$(var.Property_Manufacturer)'>

    <!--These properties will appear in Windows Explorer-->
    <Package Id='*'
             Keywords='Installer'
             Description="$(var.Property_ProductName) Installer"
             Comments='$(var.Property_Manufacturer) $(var.Property_ProductName)'
             Manufacturer='$(var.Property_Manufacturer)'
             InstallerVersion='100'
             Languages='1033'
             Compressed='yes'
             SummaryCodepage='1252' />
    
    <Media Id="1"
           Cabinet="media1.cab"
           EmbedCab="yes" />

    <!--Defining target directory structure-->
    <Directory Id='TARGETDIR'
               Name='SourceDir'>
      <!--Primary install folder: %PROGRAMFILES%\My Company\My Sample App\ ; Sub folders: Resources-->
      <Directory Id='ProgramFilesFolder'
                 Name='PFiles'>
        <Directory Id='ManufacturerFolder'
                   Name='$(var.Property_Manufacturer)'>
          <!--Application files to the primary install fodler-->
          <Directory Id='INSTALLDIR'
                     Name='$(var.Property_ProductName)'>

            <Component Id='MyCompany.MyApp'
                       Guid='{36EF4819-D4C6-4bc6-AA7D-4D41DC2E2342}'>
              <File Id='SampleApp.exe'
                    Name='SampleApp.exe'
                    DiskId='1'
                    Source='$(var.SolutionDir)\SampleApp\$(var.OutDir)SampleApp.exe'
                    KeyPath='yes'>
                <Shortcut Id="ProgramMenu.Shortcut.App"
                          Directory="ProgramMenuSubFolder"
                          Name="$(var.Property_ProductName)"
                          WorkingDirectory='INSTALLDIR'
                          Icon="AppIcon.ico"
                          IconIndex="0"
                          Advertise="yes" />
                <Shortcut Id="Desktop.Shortcut.App"
                          Directory="DesktopFolder"
                          Name="$(var.Property_ProductName)"
                          WorkingDirectory='INSTALLDIR'
                          Icon="AppIcon.ico"
                          IconIndex="0"
                          Advertise="yes" />
              </File>
            </Component>

            <Component Id='MyCompany.MyApp.Helpers'
                       Guid='{C60F6F97-CBC1-4ee7-89D8-3D4E5F72DD00}'>
              <File Id='HelperDLL'
                    Name='Helper.dll'
                    DiskId='1'
                    Source='$(var.SolutionDir)\SampleApp\$(var.OutDir)Helper.dll'
                    KeyPath='yes' />
            </Component>

            <Component Id='MyCompany.MyApp.Manual'
                       Guid='{DB40393C-2D35-4007-A0EF-E0846F1A70E4}'>
              <File Id='Manual'
                    Name='Manual.pdf'
                    DiskId='1'
                    Source='$(var.SolutionDir)\SampleApp\$(var.OutDir)Manual.pdf'
                    KeyPath='yes'>
                <Shortcut Id="ProgramMenu.Shortcut.Manual"
                          Directory="ProgramMenuSubFolder"
                          Name="Instruction Manual"
                          Advertise="yes" />
              </File>
            </Component>

            <!--Resources to the Resources sub folder-->
            <Directory Id="AppResources"
                       Name="Resources" >
              <Component Id="MyCompany.MyApp.Resources"
                         Guid="{F25B9D53-9924-4a6c-B0F7-C5188943F474}">
                <File Id="image.jpg"
                      Name="image.jpg"
                      Source="$(var.SolutionDir)\SampleApp\$(var.OutDir)Resources\image.jpg"
                      Checksum="yes"/>
              </Component>
            </Directory>
          </Directory>
        </Directory>
      </Directory>

      <!--Define Start menu folder-->
      <Directory Id="ProgramMenuFolder"
                 Name="Programs">
          <Directory Id="ProgramMenuSubFolder"
                     Name="$(var.Property_Manufacturer) $(var.Property_ProductName)">
            <Component Id="MyCompany.MyApp.Shortcut"
                       Guid="{3C08CF93-5203-49fe-B545-005C225DA334}">
              <!--Any extra folder we creare under user profile need to be marked for deletion-->
              <RemoveFolder Id='ProgramMenuSubFolder'
                            On='uninstall' />
              <!--This is also required?!-->
              <RegistryValue Root='HKCU'
                             Key='Software\[Manufacturer]\[ProductName]'
                             Type='string'
                             Value=''
                             KeyPath='yes' />
            </Component>
          </Directory>
      </Directory>

      <!--Define Desktop folder-->
      <Directory Id="DesktopFolder"
                 Name="Desktop" />
    </Directory>

    <!--Register all components under a single feature-->
    <Feature Id='Complete'
             Level='1'>
      <ComponentRef Id='MyCompany.MyApp' />
      <ComponentRef Id='MyCompany.MyApp.Helpers' />
      <ComponentRef Id='MyCompany.MyApp.Manual' />
      <ComponentRef Id='MyCompany.MyApp.Shortcut' />
      <ComponentRef Id='MyCompany.MyApp.Resources' />
    </Feature>
    
    <!-- The icon that appears in Add & Remove Programs. -->
    <Property Id="ARPPRODUCTICON"
              Value="appicon.ico" />

    <!--UI style is set to InstallDir (User will have directory selection)-->
    <UIRef Id="WixUI_InstallDir"/>
    <Property Id="WIXUI_INSTALLDIR"
              Value="INSTALLDIR" />

    <!--Sepcify license file-->
    <WixVariable Id="WixUILicenseRtf"
                 Value="license.rtf" />

    <!--Specify initial page's background image-->
    <WixVariable Id="WixUIDialogBmp"
                 Value="welcome.bmp" />

    <!--Specify subsequent page's banner image-->
    <WixVariable Id="WixUIBannerBmp"
                 Value="banner.bmp" />

    <!--Define the icon used for shortcuts and installer-->
    <Icon Id="AppIcon.ico"
          SourceFile="appicon.ico" />
  </Product>
</Wix>