Managed Extensibility Framework

New Post: Multiple metadata with a custom data type

rookster — Wed, 22 Feb 2012 19:29:11 GMT

Hi, thank you for the answer.

I tried something very similar, but with IMenuAssociationMetadata in place of Tuple<,> (in the example IExtensionMetadata is the type that comes into Lazy<T,TMetadata> when importing). This would probably require MEF to generate a backing class not only for IExtensionMetadata, but also for inner interfaces, and their inner interfaces, so there's actually no wonder it doesn't work.

What I managed to do finally was use a class instead of interface as metadata signature:

    public class ExtensionMetadata : IExtensionMetadata
    {
        public IMenuAssociationMetadata[] Associations { get; private set; }

        public ExtensionMetadata(IDictionary<string, object> metadata)
        {
            this.Associations = //create it here from dictionary
        }
    }

IMenuAssociationMetadata instances are created 'manually' in the above constructor. Of course, I'm forced to deal with Type[] and string[], but MEF seems to provide valid number of elements in each array and in the right order. I hope it's by design!

Then I can have Lazy<IExtension, ExtensionMetadata>, which exposes only the strongly-typed metadata.

Cheers,

Paul

New Post: Surpising ImportMany behavior with RegistrationBuilder

jlewicki — Wed, 22 Feb 2012 18:35:22 GMT

Thanks for the prompt reply.

Per your suggestion, I was able to get around this by using the SelectConstructor overload that provides access to the ImportBuilder, which allowed me to say: ib.AsMany(false).

Thanks! -John

New Post: Multiple metadata with a custom data type

nblumhardt — Wed, 22 Feb 2012 18:26:42 GMT

Hi,

The restriction on parameter types impacts the constants you pass into the attribute, but doesn’t restrict what you can present as properties on the attribute type. So the following attribute structure might help:

public class MenuAssociationAttribute : Attribute

{

public MenuAssociationAttribute(Type type, string name)

{

// assign to _type and _name;

}

public Tuple<Type, string> Associations { get { return Tuple.Create(_type, _name); } }
}

Then the metadata view:

public interface IMenuAssociationMetadata

{

Tuple<Type, string>[] Associations { get; }

}

Let us know how you go!

Cheers,
Nick

From: rookster [email removed]
Sent: Wednesday, February 22, 2012 7:05 AM
To: Nicholas Blumhardt
Subject: Multiple metadata with a custom data type [MEF:341118]

From: rookster

I'm attempting to export parts along with multiple metadata defined with the same attribute. As an example consider this class:

    [Export(typeof(IExtension))]

    [MenuAssociation(typeof(WindowContextMenuId), CategoryName = "window context")]

    [MenuAssociation(typeof(WorkspaceContextMenuId), CategoryName = "workspace context")]

    class ContextMenuExtension : IExtension

MenuAssociation is a MetadataAttribute that contains Type and String properties. I'd like to import IExtensions in a way that allows me to view metadata in the following form:

    public interface IExtensionMetadata

        IMenuAssociationMetadata[] Associations { get; }

    public interface IMenuAssociationMetadata

        Type Type { get; }

        string CategoryName { get; }

Each IMenuAssociationMetadata instance should contain the (Type, String) info provided by a single occurence of MenuAssociationAttribute. With this setup there's a composition exception that points to c# spec 17.1.3 about "attribute parameter types". However, according to the specification, I'm passing valid parameters to the constructor of MenuAssociationAttribute (only string and Type).

I observed that I can have:

    public interface IExtensionMetadata

        Type[] Type { get; }

        string[] CategoryName { get; }

Then I get two arrays: {"window context", "workspace context"} and {WindowContextMenuId, WorkspaceContextMenuId}, which isn't too convenient.

1. Is it at least guaranteed that the order of elements in arrays will correspond to how they are defined with MenuAssociationAttribute? (That the n-th element of the string array always corresponds to the n-th element of the type array)

2. Is there a way to get one array of (Type, string) pairs like e.g. (WindowContextMenuId, "window context") instead of two separate arrays? For my purpose I find such pairs more coherent logically .

3. Should I assume that MEF supports metadata with AllowMultiple=true, but only if the data type is one of the "attribute parameter types" mentioned in the specification?

I'm currently using MEF 2 Preview 5, if it matters.

interface IMenuAssociationMetadata

New Post: Surpising ImportMany behavior with RegistrationBuilder

nblumhardt — Wed, 22 Feb 2012 18:20:42 GMT

Hi there – thanks for the report.

This was by design, though we can see that the experience here could use a bit of improvement.

There are two ways to switch this import back to a “single” import:

1. Place the [ImportingConstructor] attribute on the SomeOtherService constructor and apply an [Import] attribute to the someService parameter

2. In the registration rule for SomeOtherService, use .AsMany(false) to configure the someService parameter

Does either option work in your scenario?

Cheers,
Nick

From: jlewicki [email removed]
Sent: Wednesday, February 22, 2012 8:49 AM
To: Nicholas Blumhardt
Subject: Surpising ImportMany behavior with RegistrationBuilder [MEF:341470]

From: jlewicki

I've run into an issue with RegistrationBuilder that I found somewhat surprising, and I might be inclined to think it could be a bug.

The issue I ran into was that I have a service (call it SomeOtherService) that depends on another service (call it ISomeService). SomeOtherService accepts a ISomeService instance in its constructor:
public SomeOtherService( ISomeService someService )
{
this.someService = someService;
}

I set up a registration builder that registers these services with a couple lines of code. Easy peasy. However when I attempt to resolve an instance of SomeOtherService, MEF throws an exception:

The importing constructor on type 'MefRegistrationIssue.SomeOtherService' is using ImportManyAttribute on parameter 'someService' with a non-assignable type. On constructor parameters the ImportManyAttribute only supports importing into types T[] or IEnumerable<T>.

I was confused by this for a bit, because clearly the SomeOtherService constructor accepts a single instance, not an enumerable.
The catch is that ISomeService itself inherits from IEnumerable<string>, which seems to trick MEF into registering the import as a ImportMany. Looking at the MEF source code (it's awesome that you put it out there!), the offending line of code is in ImportBuilder.BuildAttributes:

bool asMany = (!this._asManySpecified) ? type != StringType && typeof(IEnumerable).IsAssignableFrom(type) : this._asMany;

The condition typeof(IEnumerable).IsAssignableFrom(type) is obviously the culprit here, since ISomeService is assignable to IEnumerable. I wonder if the condition needs to be more clever here, for example by matching exactly on IEnumerable/IEnumerable<T> instead of checking for type compatibility. Or is this working exactly as intended?

Heres the test case:

using System.Collections;

using System.Collections.Generic;

using System.ComponentModel.Composition.Hosting;

using System.ComponentModel.Composition.Registration;

using System.Reflection;

namespace MefRegistrationIssue

 public interface ISomeService : IEnumerable<string>

  int GetANumber();

 public class SomeService : ISomeService

  public int GetANumber()

   return 2;

  public IEnumerator<string> GetEnumerator()

   yield return "foo";

   yield return "bar";

  IEnumerator IEnumerable.GetEnumerator()

   return this.GetEnumerator();

 public class SomeOtherService

  public SomeOtherService( ISomeService someService )

   this.someService = someService;

  public int DoWork()

   return this.someService.GetANumber();

  ISomeService someService;

 class Program

  static void Main( string[] args )

     var builder = new RegistrationBuilder();

     builder.ForType<SomeService>().Export<ISomeService>();

     builder.ForType<SomeOtherService>().Export();

     var container = new CompositionContainer(

        new AssemblyCatalog( Assembly.GetExecutingAssembly(), builder ) );

     var someOtherService =   container.GetExportedValue<SomeOtherService>();

     someOtherService.DoWork();

New Post: Inside class inherit base class which can't import .

nblumhardt — Wed, 22 Feb 2012 17:31:42 GMT

Hi – I think what Alok is asking is, how is EditViewModel<T> being exported? If it is not being exported at all, are you using something like SatisfyImportsOnce() to set its imports? Classes with imports need to be either exported themselves, or composed using one of the methods on the container, in order for their imports to be set.

Hope this helps,
Nick

From: Cuiqs [email removed]
Sent: Wednesday, February 22, 2012 5:12 AM
To: Nicholas Blumhardt
Subject: Re: Inside class inherit base class which can't import . [MEF:334351]

From: Cuiqs

the Exporting in another module.

If in the EditViewModel constractor use below code. it work fine.

 public EditViewModel()

            this.Shell = ServiceLocator.Current.GetInstance<IShellViewModel>();

            this.RegionManager = ServiceLocator.Current.GetInstance<IRegionManager>();

alokshriram wrote:

What ate you exporting?? Cannot tell from the code you have provided.

- alok

From: Cuiqs
Sent: 2/20/2012 9:09 PM
To: Alok Shriram
Subject: Inside class inherit base class which can't import . [MEF:334351]

From: Cuiqs

Public Class RoleViewModel

       public List<RoleEditViewModel> Role

get

                if (Model == null)

                    return null;

                else

                    return new List<RoleEditViewModel> { new RoleEditViewModel(this, Model.Role) };

   public class RoleEditViewModel: EditViewModel<Role>

  public RoleViewModel Parent { get; private set; }

            public RoleEditViewModel(RoleViewModel parent, Role role)

                ManageObjectLifetime = false;

                Parent = parent;

                Model = role;

  public class EditViewModel<T> : Csla.Xaml.ViewModelBase<T>

   [Import]

        public IRegionManager RegionManager { get; set; }

        [Import]

        public IShellViewModel Shell { get; set; }

Run the code ,the RegionManager & Shell  are null.

New Post: Surpising ImportMany behavior with RegistrationBuilder

jlewicki — Wed, 22 Feb 2012 16:48:59 GMT

I've run into an issue with RegistrationBuilder that I found somewhat surprising, and I might be inclined to think it could be a bug.

Here is my situation: I have a service (call it SomeOtherService) that depends on another service (call it ISomeService). SomeOtherService accepts an ISomeService instance in its constructor:
public SomeOtherService( ISomeService someService )
{
this.someService = someService;
}

I set up a registration builder that registers these services with a couple lines of code. Easy peasy. However when I attempt to resolve an instance of SomeOtherService, MEF throws an exception:

bool asMany = (!this._asManySpecified) ? type != StringType && typeof(IEnumerable).IsAssignableFrom(type) : this._asMany;

For what its worth, the actual services I am working with are third party code, and I don't have the freedom to alter the interfaces.

Heres the test case:

using System.Collections;
using System.Collections.Generic;
using System.ComponentModel.Composition.Hosting;
using System.ComponentModel.Composition.Registration;
using System.Reflection;

namespace MefRegistrationIssue
{
 public interface ISomeService : IEnumerable<string>
 {
  int GetANumber();
 }
 
 public class SomeService : ISomeService
 {
  public int GetANumber()
  {
   return 2;
  }

  public IEnumerator<string> GetEnumerator()
  {
   yield return "foo";
   yield return "bar";
  }

  IEnumerator IEnumerable.GetEnumerator()
  {
   return this.GetEnumerator();
  }
 }

 public class SomeOtherService
 {
  public SomeOtherService( ISomeService someService )
  {
   this.someService = someService;
  }

  public int DoWork()
  {
   return this.someService.GetANumber();
  }

  ISomeService someService;
 }


 class Program
 {
  static void Main( string[] args )
  {
     var builder = new RegistrationBuilder();
     builder.ForType<SomeService>().Export<ISomeService>();
     builder.ForType<SomeOtherService>().Export();

     var container = new CompositionContainer( 
        new AssemblyCatalog( Assembly.GetExecutingAssembly(), builder ) );
   
     var someOtherService =   container.GetExportedValue<SomeOtherService>();
     someOtherService.DoWork();
  }

 }
}

New Post: Multiple metadata with a custom data type

rookster — Wed, 22 Feb 2012 15:04:31 GMT

I'm attempting to export parts along with multiple metadata defined with the same attribute. As an example consider this class:

    [Export(typeof(IExtension))]
    [MenuAssociation(typeof(WindowContextMenuId), CategoryName = "window context")]
    [MenuAssociation(typeof(WorkspaceContextMenuId), CategoryName = "workspace context")]
    class ContextMenuExtension : IExtension
    {

    }

MenuAssociation is a MetadataAttribute that contains Type and String properties. I'd like to import IExtensions in a way that allows me to view metadata in the following form:

    public interface IExtensionMetadata
    {
        IMenuAssociationMetadata[] Associations { get; }
    }
    public interface IMenuAssociationMetadata
    {
        Type Type { get; }
        string CategoryName { get; }
    }

I observed that I can have:

    public interface IExtensionMetadata
    {
        Type[] Type { get; }
        string[] CategoryName { get; }
    }

Then I get two arrays: {"window context", "workspace context"} and {WindowContextMenuId, WorkspaceContextMenuId}, which isn't too convenient.

2. Is there a way to get one array of (Type, string) pairs like e.g. (WindowContextMenuId, "window context") instead of two separate arrays? For my purpose I find such pairs more coherent logically .

3. Should I assume that MEF supports metadata with AllowMultiple=true, but only if the data type is one of the "attribute parameter types" mentioned in the specification?

I'm currently using MEF 2 Preview 5, if it matters.

interface IMenuAssociationMetadata

New Post: Inside class inherit base class which can't import .

Cuiqs — Wed, 22 Feb 2012 13:12:01 GMT

the Exporting in another module.

If in the EditViewModel constractor use below code. it work fine.

 public EditViewModel()
        {
      
            this.Shell = ServiceLocator.Current.GetInstance<IShellViewModel>();
            this.RegionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
          
        }

alokshriram wrote:

What ate you exporting?? Cannot tell from the code you have provided.

- alok

From: Cuiqs
Sent: 2/20/2012 9:09 PM
To: Alok Shriram
Subject: Inside class inherit base class which can't import . [MEF:334351]

From: Cuiqs

Public Class RoleViewModel
{

       public List<RoleEditViewModel> Role
        {
            get
            {
                if (Model == null)
                    return null;
                else
                    return new List<RoleEditViewModel> { new RoleEditViewModel(this, Model.Role) };
            }
        }

   public class RoleEditViewModel: EditViewModel<Role>
        {   
  public RoleViewModel Parent { get; private set; }
            public RoleEditViewModel(RoleViewModel parent, Role role)
            {
                ManageObjectLifetime = false;
                Parent = parent;
                Model = role;
                
            }  
}

}


  public class EditViewModel<T> : Csla.Xaml.ViewModelBase<T>
{
   [Import]
        public IRegionManager RegionManager { get; set; }

        [Import]
        public IShellViewModel Shell { get; set; }

}

Run the code ,the RegionManager & Shell  are null.

New Post: Inside class inherit base class which can't import .

Cuiqs — Tue, 21 Feb 2012 12:59:02 GMT

the Exporting in another module.

If in the EditViewModel constractor use below code. it work fine.

 public EditViewModel()
        {
      
            this.Shell = ServiceLocator.Current.GetInstance<IShellViewModel>();
            this.RegionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
          
        }

New Post: Inside class inherit base class which can't import .

alokshriram — Tue, 21 Feb 2012 08:41:12 GMT

What ate you exporting?? Cannot tell from the code you have provided.

- alok

From: Cuiqs
Sent: 2/20/2012 9:09 PM
To: Alok Shriram
Subject: Inside class inherit base class which can't import . [MEF:334351]

From: Cuiqs

Public Class RoleViewModel
{

       public List<RoleEditViewModel> Role
        {
            get
            {
                if (Model == null)
                    return null;
                else
                    return new List<RoleEditViewModel> { new RoleEditViewModel(this, Model.Role) };
            }
        }

   public class RoleEditViewModel: EditViewModel<Role>
        {   
  public RoleViewModel Parent { get; private set; }
            public RoleEditViewModel(RoleViewModel parent, Role role)
            {
                ManageObjectLifetime = false;
                Parent = parent;
                Model = role;
                
            }  
}

}


  public class EditViewModel<T> : Csla.Xaml.ViewModelBase<T>
{
   [Import]
        public IRegionManager RegionManager { get; set; }

        [Import]
        public IShellViewModel Shell { get; set; }

}

Run the code ,the RegionManager & Shell  are null.

New Post: Inside class inherit base class which can't import .

Cuiqs — Tue, 21 Feb 2012 05:08:46 GMT

Public Class RoleViewModel
{

       public List<RoleEditViewModel> Role
        {
            get
            {
                if (Model == null)
                    return null;
                else
                    return new List<RoleEditViewModel> { new RoleEditViewModel(this, Model.Role) };
            }
        }

   public class RoleEditViewModel: EditViewModel<Role>
        {   
  public RoleViewModel Parent { get; private set; }
            public RoleEditViewModel(RoleViewModel parent, Role role)
            {
                ManageObjectLifetime = false;
                Parent = parent;
                Model = role;
                
            }  
}

}


  public class EditViewModel<T> : Csla.Xaml.ViewModelBase<T>
{
   [Import]
        public IRegionManager RegionManager { get; set; }

        [Import]
        public IShellViewModel Shell { get; set; }

}

Run the code ,the RegionManager & Shell  are null.

New Post: MVC4

nblumhardt — Mon, 20 Feb 2012 16:27:27 GMT

Yes, it will work. Please post details if you hit any issues.

Thanks!

Nick

New Post: Mef2P4 MVC3 How to resolve

nblumhardt — Mon, 20 Feb 2012 16:26:34 GMT

This is part of the composition provider NuGet package, so we're likely to address this before MEF 3. Sorry about the wait - we're working on a status update for MEF and should get it onto the BCL Team blog in the next few weeks.

Cheers!

Nick

New Post: MVC4

JaapM — Mon, 20 Feb 2012 15:25:22 GMT

Will MEF2P5 work with the new MVC4 beta with simply adding a runtime assembly binding from 3.0.0.0 to 4.0.0.0?

New Post: Mef2P4 MVC3 How to resolve

JaapM — Mon, 20 Feb 2012 15:17:50 GMT

Any idea if this will be fixed in MEF 2?

Or will it be suspended to MEF 3?

New Comment on "Architecture"

apo — Fri, 17 Feb 2012 11:44:06 GMT

Which tool did you used for creating the architecture figures? They are looking nice.

New Post: MEF in WPF application using MVVM Pattern,

fhnaseer — Fri, 17 Feb 2012 07:18:44 GMT

thanks, it look good but it is too complex.

New Post: MEF in WPF application using MVVM Pattern,

ido_ran — Fri, 17 Feb 2012 07:03:10 GMT

Hi,

This one looks very interesting: http://www.codeproject.com/Articles/43625/Building-an-Extensible-Application-with-MEF-WPF-an

Ido

New Post: MEF in WPF application using MVVM Pattern,

fhnaseer — Fri, 17 Feb 2012 06:59:47 GMT

I am looking for a WPF application following MVVM pattern and using MEF. I have looked on the samples. Meflook is a wpf application but doesnot follow MVVM pattern.

New Post: TypeLoadException ImportSource

Torremolinos — Tue, 14 Feb 2012 21:14:25 GMT

I was missing register the dlls into the GAC!!