title: Cannot use Mahapps in plugin project
body: <p>I am developing wpf application with MvvmCross. I have my own dialog plugin that has a alert window. It will pop up when I click on some buttons to confirm my action. Previously, alert window is just a simple wpf window. But I want to use Mahapps to style it. </p>
  
  <p>The problem is when I changed the base class of AlertWindow from window to Mahapps's MetroWindow an error has occurred "Could not find plugin type in assembly"</p>
  
  <p>Below is my code in xaml file and c# file</p>
  
  <pre><code>&lt;Controls:MetroWindow x:Class="Test.MvvmCross.Plugins.Dialog.Wpf.AlertWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
          Title="" Height="120" Width="350" SizeToContent="Height" ShowInTaskbar="False" ResizeMode="NoResize" WindowStartupLocation="CenterScreen" &gt;
      &lt;Window.Resources&gt;
          &lt;ResourceDictionary&gt;
              &lt;ResourceDictionary.MergedDictionaries&gt;
                  &lt;ResourceDictionary Source="pack://application:,,,/Test.MvvmCross.Plugins.Dialog.Wpf;component/Styles/Generic.xaml" /&gt;
              &lt;/ResourceDictionary.MergedDictionaries&gt;
          &lt;/ResourceDictionary&gt;
      &lt;/Window.Resources&gt;
  
      &lt;StackPanel Orientation="Vertical"&gt;
          &lt;TextBlock TextWrapping="Wrap" Margin="10" Text="{Binding Message}" Name="MessageTb"&gt;asdfasdf asdfasdf asdfa asdfas asdf asdf asdf&lt;/TextBlock&gt;
          &lt;DockPanel Margin="5" Background="White"&gt;
              &lt;Button DockPanel.Dock="Right" Margin="5" Height="30" Width="65" Name="NeutralButton" IsCancel="True"&gt;
                  &lt;Grid&gt;
                      &lt;ContentControl Style="{StaticResource Content1NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="NeutralContent1Textblock" Foreground="{StaticResource ButtonNotSelectedColorBrush}"/&gt;
                      &lt;/ContentControl&gt;
                      &lt;ContentControl Style="{StaticResource Content2NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="NeutralContent2Textblock" Foreground="{StaticResource ButtonTextColorBrush}" FontWeight="Bold"/&gt;
                      &lt;/ContentControl&gt;
                  &lt;/Grid&gt;
              &lt;/Button&gt;
              &lt;Button DockPanel.Dock="Right" Margin="5" Height="30" Width="65" Name="NegativeButton"&gt;
                  &lt;Grid&gt;
                      &lt;ContentControl Style="{StaticResource Content1NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="NegativeContent1Textblock" Foreground="{StaticResource ButtonNotSelectedColorBrush}"/&gt;
                      &lt;/ContentControl&gt;
                      &lt;ContentControl Style="{StaticResource Content2NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="NegativeContent2Textblock" Foreground="{StaticResource ButtonTextColorBrush}" FontWeight="Bold"/&gt;
                      &lt;/ContentControl&gt;
                  &lt;/Grid&gt;
              &lt;/Button&gt;
              &lt;Button DockPanel.Dock="Right"  Margin="5" Height="30" Width="65" Name="PositiveButton" IsDefault="True" &gt;
                  &lt;Grid&gt;
                      &lt;ContentControl Style="{StaticResource Content1NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="PositiveContent1Textblock" Foreground="{StaticResource ButtonNotSelectedColorBrush}"/&gt;
                      &lt;/ContentControl&gt;
                      &lt;ContentControl Name="PositiveContent2" Style="{StaticResource Content2NormalButtonStyle}" &gt;
                          &lt;TextBlock Name="PositiveContent2Textblock" Foreground="{StaticResource ButtonTextColorBrush}" FontWeight="Bold"/&gt;
                      &lt;/ContentControl&gt;
                  &lt;/Grid&gt;
              &lt;/Button&gt;
              &lt;Control /&gt;
          &lt;/DockPanel&gt;
      &lt;/StackPanel&gt;
  &lt;/Controls:MetroWindow&gt;
  </code></pre>
  
  <p>This is the and error message <a href="http://i.stack.imgur.com/CTDXb.png" rel="nofollow">image</a>.</p>
  
  <p>**I have updated the xaml code</p>
  
  <p>I have used Mahapps in my main project with no problem. Please let me know if you not understand what i want or anything else.</p>