c# - The type String cannot be constructed. You must configure the container to supply this value -

i have looked @ several tutorials , stackoverflow questions on how implement unity mvc 5 project, can't seem past error :

the type string cannot constructed. must configure container supply value.

i installed nuget package unity.mvc5, , registered type in unity config. have called register components method in unityconfig file.

public static class unityconfig {     public static void registercomponents()     {         var container = new unitycontainer();          // register components container here         // not necessary register controllers          // e.g. container.registertype<itestservice, testservice>();         container.registertype<istateservice, stateservice>();          dependencyresolver.setresolver(new unitydependencyresolver(container));     } }  protected void application_start() {     arearegistration.registerallareas();     routeconfig.registerroutes(routetable.routes);     unityconfig.registercomponents(); }  public class statecontroller : controller {     private readonly istateservice stateservice;      public statecontroller(istateservice stateservice)     {         this.stateservice = stateservice;     }      // get: /state/     public actionresult index()     {         return view(stateservice.getstates());     } }  public interface istateservice : idisposable {     ienumerable<state> getstates(); }  public class stateservice : istateservice {     private myappdbcontext context;     public stateservice() : this(new myappdbcontext()){}      public stateservice(myappdbcontext context)     {         this.context = context;     }      private iqueryable<state> all()     {         return context.states;     }      public ienumerable<state> getstates()     {         return this.all().tolist();                }      public void dispose()     {         context.dispose();     } } 

here stack trace:

 [invalidoperationexception: type string cannot constructed. must configure container supply value.]    microsoft.practices.objectbuilder2.dynamicmethodconstructorstrategy.guardtypeisnonprimitive(ibuildercontext context) +311    microsoft.practices.objectbuilder2.dynamicmethodconstructorstrategy.prebuildup(ibuildercontext context) +229    microsoft.practices.objectbuilder2.strategychain.executebuildup(ibuildercontext context) +274    microsoft.practices.objectbuilder2.dynamicmethodbuildplancreatorpolicy.createplan(ibuildercontext context, namedtypebuildkey buildkey) +162    microsoft.practices.objectbuilder2.buildplanstrategy.prebuildup(ibuildercontext context) +245    microsoft.practices.objectbuilder2.strategychain.executebuildup(ibuildercontext context) +274    microsoft.practices.objectbuilder2.buildercontext.newbuildup(namedtypebuildkey newbuildkey) +250    microsoft.practices.unity.objectbuilder.namedtypedependencyresolverpolicy.resolve(ibuildercontext context) +101    lambda_method(closure , ibuildercontext ) +215    microsoft.practices.objectbuilder2.c__displayclass1.b__0(ibuildercontext context) +71    microsoft.practices.objectbuilder2.dynamicmethodbuildplan.buildup(ibuildercontext context) +42    microsoft.practices.objectbuilder2.buildplanstrategy.prebuildup(ibuildercontext context) +333    microsoft.practices.objectbuilder2.strategychain.executebuildup(ibuildercontext context) +274    microsoft.practices.objectbuilder2.buildercontext.newbuildup(namedtypebuildkey newbuildkey) +250    microsoft.practices.unity.objectbuilder.namedtypedependencyresolverpolicy.resolve(ibuildercontext context) +101    lambda_method(closure , ibuildercontext ) +205    microsoft.practices.objectbuilder2.c__displayclass1.b__0(ibuildercontext context) +71    microsoft.practices.objectbuilder2.dynamicmethodbuildplan.buildup(ibuildercontext context) +42    microsoft.practices.objectbuilder2.buildplanstrategy.prebuildup(ibuildercontext context) +333    microsoft.practices.objectbuilder2.strategychain.executebuildup(ibuildercontext context) +274    microsoft.practices.objectbuilder2.buildercontext.newbuildup(namedtypebuildkey newbuildkey) +250    microsoft.practices.unity.objectbuilder.namedtypedependencyresolverpolicy.resolve(ibuildercontext context) +101    lambda_method(closure , ibuildercontext ) +209    microsoft.practices.objectbuilder2.c__displayclass1.b__0(ibuildercontext context) +71    microsoft.practices.objectbuilder2.dynamicmethodbuildplan.buildup(ibuildercontext context) +42    microsoft.practices.objectbuilder2.buildplanstrategy.prebuildup(ibuildercontext context) +333    microsoft.practices.objectbuilder2.strategychain.executebuildup(ibuildercontext context) +274    microsoft.practices.unity.unitycontainer.dobuildup(type t, object existing, string name, ienumerable`1 resolveroverrides) +383  [resolutionfailedexception: resolution of dependency failed, type = "myapp.mvc.controllers.statecontroller", name = "(none)". exception occurred while: while resolving. exception is: invalidoperationexception - type string cannot constructed. must configure container supply value. ----------------------------------------------- @ time of exception, container was:    resolving myapp.mvc.controllers.statecontroller,(none)   resolving parameter "stateservice" of constructor myapp.mvc.controllers.statecontroller(myapp.service.services.istateservice stateservice)     resolving myapp.service.services.stateservice,(none) (mapped myapp.service.services.istateservice, (none))     resolving parameter "context" of constructor myapp.service.services.stateservice(myapp.data.dal.myappdbcontext context)       resolving myapp.data.dal.myappdbcontext,(none)       resolving parameter "connectionstring" of constructor myapp.data.dal.myappdbcontext(system.string connectionstring, system.data.entity.infrastructure.dbcompiledmodel model)         resolving system.string,(none) ]    microsoft.practices.unity.unitycontainer.dobuildup(type t, object existing, string name, ienumerable`1 resolveroverrides) +446    microsoft.practices.unity.unitycontainer.dobuildup(type t, string name, ienumerable`1 resolveroverrides) +50    microsoft.practices.unity.unitycontainer.resolve(type t, string name, resolveroverride[] resolveroverrides) +48    microsoft.practices.unity.unitycontainerextensions.resolve(iunitycontainer container, type t, resolveroverride[] overrides) +61    unity.mvc5.unitydependencyresolver.getservice(type servicetype) +140    system.web.mvc.defaultcontrolleractivator.create(requestcontext requestcontext, type controllertype) +87  [invalidoperationexception: error occurred when trying create controller of type 'myapp.mvc.controllers.statecontroller'. make sure controller has parameterless public constructor.]    system.web.mvc.defaultcontrolleractivator.create(requestcontext requestcontext, type controllertype) +247    system.web.mvc.defaultcontrollerfactory.getcontrollerinstance(requestcontext requestcontext, type controllertype) +438    system.web.mvc.defaultcontrollerfactory.createcontroller(requestcontext requestcontext, string controllername) +257    system.web.mvc.mvchandler.processrequestinit(httpcontextbase httpcontext, icontroller& controller, icontrollerfactory& factory) +326    system.web.mvc.mvchandler.beginprocessrequest(httpcontextbase httpcontext, asynccallback callback, object state) +157    system.web.mvc.mvchandler.beginprocessrequest(httpcontext httpcontext, asynccallback callback, object state) +88    system.web.mvc.mvchandler.system.web.ihttpasynchandler.beginprocessrequest(httpcontext context, asynccallback cb, object extradata) +50    system.web.callhandlerexecutionstep.system.web.httpapplication.iexecutionstep.execute() +301    system.web.httpapplication.executestep(iexecutionstep step, boolean& completedsynchronously) +155

what might doing wrong?

update

i added following code registercomponents method in unityconfig class , seems working:

container.registerinstance<stateservice>(new stateservice()); 

none of tutorials show need this, , feel example case i'm using pretty standard. why need line? don't know unity yet, why still curious.

your stateservice trying resolve "context". recommend keep context out of di mappings keep out of constructors want resolve.

resolving parameter "context" of constructor myapp.service.services.stateservice(myapp.data.dal.myappdbcontext context)