Xamarin Forms Previewer在UnityContainer.RegisterInstance上获取ArgumentNullException

Question

I am trying to use Xamarin Forms Previewer in my Project with MVVM Prism and Unity Container and I am getting this error:

Here is the extracted stack for reference:

Xamarin.VisualStudio.ActivationManager|Error|0| The renderer encountered an error while rendering this file: System.ArgumentNullException: Value cannot be null. Parameter name: instance

at Microsoft.Practices.Unity.UnityContainer.RegisterInstance (System.Type t, System.String name, System.Object instance, Microsoft.Practices.Unity.LifetimeManager lifetime) in :0

at Microsoft.Practices.Unity.UnityContainerExtensions.RegisterInstance[TInterface] (Microsoft.Practices.Unity.IUnityContainer container, TInterface instance) in :0

at SellerNS.Bootstrapper.RegisterTypes () in C:\\Users\\myrepo\\Bootstrapper.cs:48

at Prism.Unity.UnityBootstrapper.Run () in :0

at Prism.Bootstrapper.Run (Xamarin.Forms.Application app) in :0

at SellerNS.App..ctor () in C:\\Users\\myrepo\\Seller\\App.xaml.cs:20

at at offset 12 in file:line:column :0:0

at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) in /Users/builder/data/lanes/4009/3a62f1ea/source/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:661

I am using:

• Visual Studio 2015 - 14.0.25424.00
• Update 3 JDK 1.8.0_121
• Xamarin 4.3.0.789-cycle9
• Prism.Forms 6.0.1
• Prism.Unity 6.1.1
• Unity 4.0.1

Any idea how to fix it?

Answer 1

I was getting a similar error with the Xamarin Forms Previewer when using Prism and it was resolved by adding a empty default constructor in App.xaml.cs as indicated here: https://github.com/PrismLibrary/Prism/issues/1037

So adding public App() : this(null) { } to App.xaml.cs worked for me.

Also, once I made the suggested change above, I had to clean the whole solution, rebuild it and then restart Visual Studio before launching the Xamarin.Forms Previewer again to get it all working as required.