Le problème est que vous mélangez les versions MvvmCross.
Donc, si vous regardez votre packages.config pour votre coeur:
<?xml version="1.0" encoding="utf-8"?>
<packages>
<package id="MvvmCross" version="4.4.0" targetFramework="portable45-net45+win8+wpa81" />
<package id="MvvmCross.Binding" version="4.4.0" targetFramework="portable45-net45+win8+wpa81" />
<package id="MvvmCross.Core" version="4.4.0" targetFramework="portable45-net45+win8+wpa81" />
<package id="MvvmCross.Platform" version="4.4.0" targetFramework="portable45-net45+win8+wpa81" />
</packages>
Ce sont la version 4.4.0
Ensuite, si nous regardons le projet Droid:
<?xml version="1.0" encoding="utf-8"?>
<packages>
<package id="MvvmCross" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Binding" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Core" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Droid.Shared" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Droid.Support.Core.UI" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Droid.Support.Fragment" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Droid.Support.V7.AppCompat" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Droid.Support.V7.RecyclerView" version="5.0.2" targetFramework="monoandroid70" />
<package id="MvvmCross.Platform" version="5.0.2" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Animated.Vector.Drawable" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Annotations" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Compat" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Core.UI" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Core.Utils" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Design" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Fragment" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Media.Compat" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Transition" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.v7.AppCompat" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.v7.RecyclerView" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Android.Support.Vector.Drawable" version="25.3.1" targetFramework="monoandroid70" />
<package id="Xamarin.Build.Download" version="0.4.3" targetFramework="monoandroid70" />
</packages>
Ce sont la version 5.0.2, qui est plus récente que 4.4.0. Consolidez vos packages et utilisez les mêmes versions pour tous vos projets.
Changement à tous utiliser la version 5.0.2 travaillé. Merci beaucoup pour votre aide. –