windows phone 7 - MVVM-light There is already a factory registered for INavigationService -

i'm trying adjust wp8 project self made mvvm implementation mvvm light.

the application compiles without errors, when open mainpage.xaml in expression blend, error:

class project.services.inavigationservice registered. app.xaml

my viewmodellocator.cs:

    /// <summary>     /// initializes new instance of viewmodellocator class.     /// </summary>     public viewmodellocator()     {         servicelocator.setlocatorprovider(() => simpleioc.default);          if (viewmodelbase.isindesignmodestatic)         {          }         else         {             if (!simpleioc.default.isregistered<inavigationservice>())             {                 simpleioc.default.register<inavigationservice>(() => new navigationservice());             }         }          simpleioc.default.register<mainpage>();         simpleioc.default.register<settingseditviewmodel>();     } 

as can see code comment, i've tried fix supposed here, i'm still getting error in blend. there no other place left register inavigationservice, problem?

any ideas? :)

i had same issue, , seems visual studio issue in combination xaml-designer, static factories/locators , design-time creation of objects. however: solutions following:

1. register without factory (not recommended)

   simpleioc.default.register<inavigationservice>();

2. or if want use factory, unregister before registering factory

   simpleioc.default.unregister<inavigationservice>(); simpleioc.default.register<inavigationservice>(() => new navigationservice());

3. prevent viewmodellocator being created more once designer/blend making constructor static

   static viewmodellocator() { ... }

the error cumbersome happen in scenario: create objects during design-time (the viewmodellocator within app.xaml probably) , whenever change in code, compiler triggered , viewmodellocator gets re-created without ever unregistering services. therefore complain in factory has been registered. in theory, when registering classes without factories multiple times, there should error as-well.