title: Animate Insertions to ItemsControl
body: <p>I'm finding WPF inscrutable at times. Given the following XAML how would one add triggers to animate (slide down, fade in) new items added to the ObservableCollection Timeline. I've seen various examples for list boxes but nothing for items control.</p>
  
  <pre><code>&lt;Grid&gt;
      &lt;ScrollViewer&gt;
          &lt;ItemsControl Name="TimelineItem"
                        ItemsSource="{Binding Timeline}"
                        Style="{StaticResource TimelineStyle}"
                        ItemContainerStyle="{StaticResource TweetItemStyle}"&gt;
              &lt;ItemsControl.ItemTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;Grid VerticalAlignment="Top"
                            HorizontalAlignment="Left"&gt;
                          &lt;Grid.ColumnDefinitions&gt;
                              &lt;ColumnDefinition Style="{StaticResource TweetImageColumnStyle}" /&gt;
                              &lt;ColumnDefinition /&gt;
                          &lt;/Grid.ColumnDefinitions&gt;
                          &lt;Grid.RowDefinitions&gt;
                              &lt;RowDefinition /&gt;
                              &lt;RowDefinition /&gt;
                              &lt;RowDefinition /&gt;
                              &lt;RowDefinition /&gt;
                          &lt;/Grid.RowDefinitions&gt;
                          &lt;Rectangle Grid.Column="0"
                                     Style="{StaticResource TweetImageStyle}"&gt;
                              &lt;Rectangle.Fill&gt;
                                  &lt;ImageBrush ImageSource="{Binding ProfileImageUrl}" /&gt;
                              &lt;/Rectangle.Fill&gt;
                          &lt;/Rectangle&gt;
                          &lt;StackPanel Grid.Column="1"&gt;
                              &lt;Grid&gt;
                                  &lt;Grid.ColumnDefinitions&gt;
                                      &lt;ColumnDefinition Width="*" /&gt;
                                      &lt;ColumnDefinition Width="Auto" /&gt;
                                  &lt;/Grid.ColumnDefinitions&gt;
                                  &lt;TextBlock Grid.Column="0"
                                             Style="{StaticResource TweetNameStyle}"
                                             Text="{Binding Name}" /&gt;
                                  &lt;TextBlock Grid.Column="1"
                                             Style="{StaticResource TweetTimeStyle}"
                                             Text="{Binding TimeAgo}" /&gt;
                              &lt;/Grid&gt;
                              &lt;Controls:TextBlockMarkup Grid.Row="1"
                                                        Grid.Column="1"
                                                        Markup="{Binding MarkupText}"
                                                        Style="{StaticResource TweetStyle}" /&gt;
                          &lt;/StackPanel&gt;
                          &lt;Separator Grid.Row="2"
                                     Grid.ColumnSpan="2"
                                     Style="{StaticResource TweetSeparatorTop}" /&gt;
                          &lt;Separator Grid.Row="3"
                                     Grid.ColumnSpan="2"
                                     Style="{StaticResource TweetSeparatorBottom}" /&gt;
                      &lt;/Grid&gt;
                  &lt;/DataTemplate&gt;
              &lt;/ItemsControl.ItemTemplate&gt;
          &lt;/ItemsControl&gt;
      &lt;/ScrollViewer&gt;
  &lt;/Grid&gt;
  </code></pre>