title: The name "AppClass" does not exist in the namespace "..." when inheriting UWP Application class from another Application-based class
body: <p>What I want to achieve is just to inherit UWP App class not from Windows.UI.Xaml.Application class, but from some base class, inherited from the "standard" one.</p>
  
  <p>However, when I do it:</p>
  
  <pre><code>namespace MyNamespace
  {
      sealed partial class App : MyUwpBaseApplication
      {
          public App()
          {
              this.InitializeComponent();
          }
      }
  }
  </code></pre>
  
  <p>and xaml:</p>
  
  <pre><code>&lt;local:MyUwpBaseApplication
      x:Class="MyNamespace.App"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:MyNamespace"&gt;
  
  &lt;/local:MyUwpBaseApplication&gt;
  </code></pre>
  
  <p>I receive both: the design time error in XAML designer as well as compilation error:</p>
  
  <blockquote>
    <p>Error XDG0008 The name "MyUwpBaseApplication" does not exist in the
    namespace
    "using:MyNamespace".  MyNamespace App.xaml    1</p>
  </blockquote>
  
  <p><em>I need the base class to use MvvmCross and Xamarin.Forms. But the error I receive is generic, not related to any of those.</em></p>
  
  <p>Visual Studio: 15.7.
  Windows: 10 Fall Creators Update.</p>
  
  <p>How can I handle that? </p>