title: DataGrid won't update ViewModel
body: <p>I've got a datagrid which is bound to an ObservableCollection of the ViewModel below. The Datagrid will display all values correctly, so the binding seems to be working, but if I change some value the Grid won't call the setter's of my VM. Could somebody tell me why?</p>
  
  <p>Here's my ViewModel:</p>
  
  <pre><code>    public class DocumentVm : ViewModelBase
  {
      private Document document;
      public bool IsNew { get; private set; }
      public Document Document {
          get { return document; }
      }
  
      public DocumentVm(Document document)
      {
          this.document = document;
          IsNew = false;
      }
  
      public DocumentVm(Document document, bool isNew)
      {
          this.document = document;
          IsNew = isNew;
      }
  
      public String Name 
      {
          get { return document.Name; }
          set { document.Name = value; RaisePropertyChangedEvent("Name");}
      }
  
      public String Path
      {
          get { return document.Path; }
          set { document.Path = value; }
      }
  
      public String Metadata
      {
          get { return document.Metadata; }
          set { document.Metadata = value; }
      }
  
      public int SpeechId
      {
          get { return document.SpeechId; }
          set { document.SpeechId = value; }
      }
  
  }
  </code></pre>
  
  <p>Here is the XAML Code:</p>
  
  <pre><code>&lt;DataGrid Margin="3" Grid.Row="7" Grid.Column="1" BorderThickness="0" 
        ItemsSource="{Binding Path=CurrentSpeech.Documents, Mode=TwoWay}" 
        SelectedItem="{Binding Path=CurrentSpeech.CurrentDocument, Mode=TwoWay}"&gt;
  &lt;DataGrid.Columns&gt;
      &lt;DataGridTemplateColumn Header="Name" Width="SizeToCells"&gt;
          &lt;DataGridTemplateColumn.CellTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;TextBox Text="{Binding Name, Mode=TwoWay}" /&gt;
              &lt;/DataTemplate&gt;
          &lt;/DataGridTemplateColumn.CellTemplate&gt;
      &lt;/DataGridTemplateColumn&gt;
      &lt;DataGridTemplateColumn Header="MetaDaten" Width="SizeToCells"&gt;
          &lt;DataGridTemplateColumn.CellTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;TextBox Text="{Binding Metadata, Mode=TwoWay}" /&gt;
              &lt;/DataTemplate&gt;
          &lt;/DataGridTemplateColumn.CellTemplate&gt;
      &lt;/DataGridTemplateColumn&gt;
      &lt;DataGridTemplateColumn Header="Pfad" Width="SizeToCells"&gt;
          &lt;DataGridTemplateColumn.CellTemplate&gt;
              &lt;DataTemplate&gt;
                  &lt;TextBlock Text="{Binding Path}" /&gt;
              &lt;/DataTemplate&gt;
          &lt;/DataGridTemplateColumn.CellTemplate&gt;
      &lt;/DataGridTemplateColumn&gt;
  &lt;/DataGrid.Columns&gt;
  </code></pre>
  
  <p></p>
  
  <p>Thank you all!</p>