title: Xamarin error cs0263 partial declarations must not specify base classes
body: <p>I have already looked to similar answers and I don't know why I am still have this error:</p>
  
  <pre><code>Severity    Code    Description Project File    Line    Suppression State
  Error   CS0263  Partial declarations of 'MainPage' must not specify different base classes  MyNavDraw.Android   (my path ...)\MainPage.xaml.cs  13  Active
  </code></pre>
  
  <p>MainPage.xaml.cs:</p>
  
  <pre><code>namespace MyNavDraw
  {
  
      public partial class MainPage : MasterDetailPage
      {
      ...
  </code></pre>
  
  <p>MainPage.xaml</p>
  
  <pre><code>&lt;MasterDetailPage xmlns="http://xamarin.com/schemas/2014/forms"
               xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
               xmlns:local="clr-namespace:MyNavDraw"
               x:Class="MyNavDraw.MasterDetailPage"&gt;
  
      &lt;MasterDetailPage.Master&gt;
      ...
  </code></pre>
  
  <p>What I tried so far:</p>
  
  <p>In xaml I have replaced the tag to:</p>
  
  <pre><code>&lt;we:MainPage ...
  </code></pre>
  
  <p>I checked "x:Class" and I think is correct the syntax, I have restarted the VS and I built again the solution. </p>
  
  <p>I use Xamarin with VS 2017. </p>
  
  <p>After a day (from this post question) I tried to put in comments the code of "MainPage.xaml" file. Then I saved it, I removed comments, saved it again and built the solution. I have a new error in built:</p>
  
  <pre><code>No way to resolve conflict between "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e". Choosing "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" arbitrarily.
  </code></pre>
  
  <p>I have an other problem when I debug the app to my physical phone (android).</p>
  
  <p>In My.Nav.Draw.Droid.MainPage.xaml.g.cs I have an exception Unhandled error.</p>
  
  <pre><code> global::Xamarin.Forms.Xaml.Extensions.LoadFromXaml(this, typeof(MainPage));
  </code></pre>
  
  <p>What can be wrong?</p>