title: reference from xaml to public class in .cs class file
body: <p>I have in my WPF project file RssInfo.cs in which I have public class</p>
  
  <pre><code>public class DoubleRangeRule : ValidationRule
  {
      public double Min { get; set; }
      public double Max { get; set; }
  
      public override System.Windows.Controls.ValidationResult Validate(object value,
                                                 CultureInfo cultureInfo)
      {
         ...
      }
  }
  </code></pre>
  
  <p>and from my XAML code in WPF window class I neet to get to this DoubleRangeRule class..  </p>
  
  <pre><code>&lt;!-- reference to my project, all my files are in the WpfCzytanieRSS namespace --&gt;
  xmlns:valRule="clr-namespace:WpfCzytanieRSS;assembly=WpfCzytanieRSS" 
  
  &lt;TextBox Validation.ErrorTemplate="{StaticResource TextBoxErrorTemplate}"
           Name="tbTitle"&gt;
    &lt;TextBox.Text&gt;
      &lt;Binding Path="Nazwa" UpdateSourceTrigger="PropertyChanged"&gt;
        &lt;Binding.ValidationRules&gt;
          &lt;valRule:DoubleRangeRule Min="0.5" Max="10"/&gt; //error place
        &lt;/Binding.ValidationRules&gt;
      &lt;/Binding&gt;
    &lt;/TextBox.Text&gt;
  &lt;/TextBox&gt;
  </code></pre>
  
  <p>And i get two errors:  </p>
  
  <p><strong>Error 1</strong>  </p>
  
  <p>The tag 'DoubleRangeRule' does not exist in XML namespace 'clr-namespace:WpfCzytanieRSS;assembly=WpfCzytanieRSS'.</p>
  
  <p><strong>Error 2</strong>  </p>
  
  <p>The type 'valRule:DoubleRangeRule' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built.</p>
  
  <p>Please help to get to class <em>DoubleRangeRule</em>!</p>