title: The namespace prefix "system" is not defined
body: <p>I am getting an error on my XAML markup. I am trying to bind a master/child data grid to a dataset (dataset is linked to a SQLite database). My XAML is:</p>
  
  <pre><code>&lt;Window x:Class="TabletTester7.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:local="clr-namespace:TabletTester7"
          xmlns:dg="http://schemas.microsoft.com/wpf/2008/toolkit"
          xmlns:System="clr-namespace:System;assembly=mscorlib"
          Title="MainWindow" Height="350" Width="525"&gt;
  
      &lt;Window.Resources&gt;
          &lt;ObjectDataProvider x:Key="FeaturesDataProvider"
              ObjectType="{x:Type local:FeaturesDataProvider}"/&gt;
          &lt;ObjectDataProvider x:Key="ChannelsDataProvider"
              ObjectType="{x:Type local:ChannelsDataProvider}"/&gt;
  
          &lt;ObjectDataProvider x:Key="Feature"
            ObjectInstance="{StaticResource FeaturesDataProvider}"
            MethodName="GetDefaultView"/&gt;
          &lt;ObjectDataProvider x:Key="ChannelsByFeature"
            ObjectInstance="{StaticResource ChannelsDataProvider}"
            MethodName="GetChannelsByFeature"&gt;
              &lt;ObjectDataProvider.MethodParameters&gt;
                  &lt;x:Static Member="system:String.Empty"/&gt; &lt;!--Error here--&gt;
              &lt;/ObjectDataProvider.MethodParameters&gt;
          &lt;/ObjectDataProvider&gt;
  
      &lt;/Window.Resources&gt;
      &lt;Grid Margin="0,0,0,-2"&gt;
  
          &lt;DataGrid Name="dgFeatures" ItemsSource="{Binding Source={StaticResource Feature}}" 
                    Margin="0,0,0,179" 
                    AutoGenerateColumns="False" 
                    IsSynchronizedWithCurrentItem="false" 
                    RowEditEnding="dataGrid_RowEditEnding"
                    SelectedValuePath="Feature_Id"
                    SelectionChanged="dgFeatures_SelectionChanged"
                    Grid.Row="0"&gt;
              &lt;DataGrid.Columns&gt;
                  &lt;DataGridTextColumn Header="Feature ID" Binding="{Binding Feature_Id}"&gt;&lt;/DataGridTextColumn&gt;
                  &lt;DataGridTextColumn Header="Feature ID" Binding="{Binding Feature_Name}"&gt;&lt;/DataGridTextColumn&gt;
                  &lt;DataGridTemplateColumn Header="Date"&gt;
                      &lt;DataGridTemplateColumn.CellTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;DatePicker SelectedDate="{Binding Date}" BorderThickness="0" /&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/DataGridTemplateColumn.CellTemplate&gt;
                  &lt;/DataGridTemplateColumn&gt;
  
              &lt;/DataGrid.Columns&gt;
          &lt;/DataGrid&gt;
          &lt;DataGrid Name="dhChannel" 
                    ItemsSource="{Binding Source={StaticResource ChannelsByFeature}}" 
                    Margin="0,148,0,0"
                    Grid.Row="1"
                    AutoGenerateColumns="False"
                    &gt;
              &lt;DataGrid.Columns&gt;
                  &lt;DataGridTextColumn Header="Channel Path" Binding="{Binding Channel_Path}"&gt;&lt;/DataGridTextColumn&gt;
              &lt;/DataGrid.Columns&gt;
          &lt;/DataGrid&gt;
  
  
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>The method I am trying to call has a signature of</p>
  
  <pre><code>public DataView GetChannelsByFeature(string featureId)
  </code></pre>
  
  <p>On the line <code>&lt;x:Static Member="system:String.Empty"/&gt;</code> I get two errors:</p>
  
  <pre><code>The namespace prefix "system" is not defined.
  </code></pre>
  
  <p>and</p>
  
  <pre><code>String is not supported in a Windows Presentation Foundation (WPF) project.
  </code></pre>
  
  <p>How can I define this method parameter?</p>