“Cannot access a disposed object” after minor code modification

Question

Using ASP.NET MVC5, EF6 & Ninject as Backend, AngularJS as frontend with token based auth (JWT).

We recently had to enable @ chars in the user names. Base on this answer in the Startup.cs (called by Ninject registration code, see below), we replaced

UserManagerFactory = () => new ApplicationUserManager(new UserStore<IdentityUser>(new SecurityDbContext()));

with

var userManager = new ApplicationUserManager(new UserStore<IdentityUser>(new SecurityDbContext()));
var validator = new UserValidator<IdentityUser>(userManager)
{
    AllowOnlyAlphanumericUserNames = false
};
userManager.UserValidator = validator;
UserManagerFactory = () => userManager;

This allows the registration of user name with @ signs as wished. However, logging into the application (even with "normal" usernames), became buggy: While the first login after start of the server works as usual, any subsequent login creates the following exception:

Cannot access a disposed object.
Object name: 'ApplicationUserManager'.

Detailed error message:

Source Error: 
Line 18:         public override async Task FindAsync(string userName, string password)
Line 19:         {
Line 20:             var result = await base.FindAsync(userName, password);
Line 21:             if (result == null)
Line 22:             {

Source File: 
xyz\Infrastructure\ApplicationUserManager.cs    Line: 20 

Stack Trace: 

[ObjectDisposedException: Cannot access a disposed object.Object name: 'ApplicationUserManager'.]   Microsoft.AspNet.Identity.UserManager`1.ThrowIfDisposed() +99   Microsoft.AspNet.Identity.d__15.MoveNext() +128   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() +24   xyz.Infrastructure.d__0.MoveNext() in xzy\Infrastructure\ApplicationUserManager.cs:20   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() +24   xyz.Infrastructure.d__0.MoveNext() in xyz\Infrastructure\ApplicationOAuthProvider.cs:39   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter.GetResult() +21   Microsoft.Owin.Security.OAuth.d__3a.MoveNext() +862   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() +24   Microsoft.Owin.Security.OAuth.d__1e.MoveNext() +2335   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter.GetResult() +21   Microsoft.Owin.Security.OAuth.d__0.MoveNext() +1728   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() +24   Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +664   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter.GetResult() +21   Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +937   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +93   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +52   System.Runtime.CompilerServices.TaskAwaiter.GetResult() +21   Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +937   System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() +22   Microsoft.Owin.Host.SystemWeb.Infrastructure.ErrorState.Rethrow() +33   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End(IAsyncResult ar) +150   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork(IAsyncResult ar) +42   System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +415   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

I guess it has something to do with Ninject, so here's a bit more background: the above changed code is called from the NinjectWebCommon.cs:

kernel.Bind<IUserService>()
    .To<UserService>()
    .WithConstructorArgument("userManager", Startup.UserManagerFactory());

Frank Frank · Accepted Answer · 2014-12-06T23:50:37

Problem: This is an object lifetime error.

Solution: Replace your code with the following.

UserManagerFactory = () => 
{
    var userManager = new ApplicationUserManager(new UserStore<IdentityUser>(new SecurityDbContext()));
    var validator = new UserValidator<IdentityUser>(userManager)
    {
        AllowOnlyAlphanumericUserNames = false
    };
    userManager.UserValidator = validator;

    return userManager;
};

Explanation:

Every time your controller needs an IUserService, Ninject goes ahead and wants to construct a new UserService.
The UserService(IUserManager userManager) constructor cannot be called without a userManager, so Ninject calls Startup.UserManagerFactory(), as configured.
In your case, UserManagerFactory is a lambda expression that returns the captured variable userManager. This will always be the same instance.
The first time, this works as expected. When the request has been processed, Dispose is called on your user manager instance.
When the next request needs to be processed, the already disposed instance is used again. This will fail.
The corrected version is also a lambda expression, but this time we create a new instance every time.

“Cannot access a disposed object” after minor code modification

1 Answers