asked on

The composition remains unchanged error while using MEF in global.asax (Fisharoo ASP.net 4 Social Networking Book)

Hi I have following code in Global.asax
------------------------ Global.asax -----------------------------------
[Import]
public IRedirector redir;
[Import]
public ILogger log;
protected void Application_Start(object sender, EventArgs e)
{
MEFManager.Compose(this);
log.EnsureInitialized();
}

protected void Application_Error(object sender, EventArgs e)
{
MEFManager.Compose(this);

log.Error(sender, "Error caught by the Global.asax: " + Server.GetLastError().Message);
redir.GoToErrorPage();
}
---------------------------------------------------------------------- End

This is Compose method
--------------------------------MEFManager.cs--------------------------------------

public static void Compose(object o)
{
var container = new CompositionContainer(
new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, @"bin\MEFBin")));
var batch = new CompositionBatch();
batch.AddPart(o);
container.Compose(batch); //Error always occurs here
}
---------------------------------------
Its throwing following error on aplication start running and when it runs to the

The composition remains unchanged. The changes were rejected because of the following error(s): The composition produced multiple composition errors, with 2 root causes. The root causes are provided below. Review the CompositionException.Errors property for more detailed information.

1) No valid exports were found that match the constraint '((exportDefinition.ContractName == "Fisharoo.Interfaces.IRedirector") AndAlso (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") AndAlso "Fisharoo.Interfaces.IRedirector".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))', invalid exports may have been rejected.

Resulting in: Cannot set import 'Web.Global.redir (ContractName="Fisharoo.Interfaces.IRedirector")' on part 'ASP.global_asax'.
Element: Web.Global.redir (ContractName="Fisharoo.Interfaces.IRedirector") --> ASP.global_asax

2) No valid exports were found that match the constraint '((exportDefinition.ContractName == "Fisharoo.Interfaces.ILogger") AndAlso (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") AndAlso "Fisharoo.Interfaces.ILogger".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))', invalid exports may have been rejected.

Resulting in: Cannot set import 'Web.Global.log (ContractName="Fisharoo.Interfaces.ILogger")' on part 'ASP.global_asax'.
Element: Web.Global.log (ContractName="Fisharoo.Interfaces.ILogger") --> ASP.global_asax

I am new to MEF. What is this error about? I googled it, but could not solve ?

ASKER CERTIFIED SOLUTION

Rouneh10

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etowa

ASKER

@Rouneh10
I did put the .dll files into the nin\MEFBin folder and this error is gone a new error is generated as:

The composition produced multiple composition errors, with 2 root causes. The root causes are provided below. Review the CompositionException.Errors property for more detailed information.

1) Cannot populate the collection 'Fisharoo.Components.UserSession._webContext' because it does not implement ICollection<T> or is read-only. If the collection is not IEnumerable<T> or T[] it must implement ICollection<T> and be either pre-initialized or be writable with a default constructor.

Resulting in: Cannot activate part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession --> Fisharoo.Components.UserSession

Resulting in: An exception occurred while trying to create an instance of type 'Fisharoo.Components.UserSession'.

Resulting in: Cannot activate part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession --> Fisharoo.Components.UserSession --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot get export 'Fisharoo.Components.UserSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession")' from part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession") --> Fisharoo.Components.UserSession --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot set import 'Fisharoo.Web.Site._userSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession")' on part 'ASP.site_master'.
Element: Fisharoo.Web.Site._userSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession") --> ASP.site_master

2) Cannot populate the collection 'Fisharoo.Components.UserSession._webContext' because it does not implement ICollection<T> or is read-only. If the collection is not IEnumerable<T> or T[] it must implement ICollection<T> and be either pre-initialized or be writable with a default constructor.

Resulting in: Cannot activate part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession --> Fisharoo.Components.UserSession

Resulting in: An exception occurred while trying to create an instance of type 'Fisharoo.Components.UserSession'.

Resulting in: Cannot activate part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession --> Fisharoo.Components.UserSession --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot get export 'Fisharoo.Components.UserSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession")' from part 'Fisharoo.Components.UserSession'.
Element: Fisharoo.Components.UserSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession") --> Fisharoo.Components.UserSession --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot set import 'Fisharoo.Components.Navigation._userSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession")' on part 'Fisharoo.Components.Navigation'.
Element: Fisharoo.Components.Navigation._userSession (ContractName="Fisharoo.DataAccess.Interfaces.IUserSession") --> Fisharoo.Components.Navigation --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot get export 'Fisharoo.Components.Navigation (ContractName="Fisharoo.Interfaces.INavigation")' from part 'Fisharoo.Components.Navigation'.
Element: Fisharoo.Components.Navigation (ContractName="Fisharoo.Interfaces.INavigation") --> Fisharoo.Components.Navigation --> DirectoryCatalog (Path="C:\Akoraba\Fisharoo\Web\bin\MEFBin")

Resulting in: Cannot set import 'Fisharoo.Web.Site._navigation (ContractName="Fisharoo.Interfaces.INavigation")' on part 'ASP.site_master'.
Element: Fisharoo.Web.Site._navigation (ContractName="Fisharoo.Interfaces.INavigation") --> ASP.site_master

I dont see why this error keeps ocurring now...
Still trying to solve but your help is much appreciated

SOLUTION

Rouneh10

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etowa

ASKER

Yes i have Import
[Import]
private IWebContext _webContext;
in my UserSession.cs
is that what is causing the error.
IWebcontext.cs----------------------
namespace Fisharoo.DataAccess.Interfaces
{
public interface IWebContext
{
void ClearSession();
bool ContainsInSession(string key);
void RemoveFromSession(string key);
bool LoggedIn { get; set; }
string Username { get; set; }
Account CurrentUser { get; set; }
string CaptchaImageText { get; set; }
string UsernameToVerify { get; }
}
UserSession is this

using Fisharoo.DataAccess.Interfaces;
using Fisharoo.Interfaces;
using Fisharoo.DataAccess;
using Fisharoo.Common;

namespace Fisharoo.Components
{
[Export(typeof(IUserSession))]
public class UserSession : IUserSession
{
[Import]
private IWebContext _webContext;

public UserSession()
{
MEFManager.Compose(this);
//_webContext = ObjectFactory.GetInstance<IWebContext>();
}

public bool LoggedIn
{
get
{
return _webContext.LoggedIn;
}
set
{
_webContext.LoggedIn = value;
}
}

public Account CurrentUser
{
get
{
return _webContext.CurrentUser;
}
set
{
_webContext.CurrentUser = value;
}
}

public string Username
{
get
{
return _webContext.Username;
}

set
{
_webContext.Username = value;
}
}
}
}
}
------------------------------------------

Rouneh10

Make your _webContext a property.

[Import]
private IWebContext _webContext { get; set; }

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etowa

ASKER

Got it working