EntranceThemeTransition not working on UWP?

Question

Do the transitions work in apps for the Universal Windows Plattform (UWP) / Windows 10?

I pasted the following code into an empty page, but the animation wouldn't work.

<ItemsControl Grid.Row="1" x:Name="rectangleItems">
    <ItemsControl.ItemContainerTransitions>
        <TransitionCollection>
            <EntranceThemeTransition/>
        </TransitionCollection>
    </ItemsControl.ItemContainerTransitions>
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <WrapGrid Height="400"/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>

    <!-- The sequence children appear depends on their order in 
     the panel's children, not necessarily on where they render
     on the screen. Be sure to arrange your child elements in
     the order you want them to transition into view. -->
    <ItemsControl.Items>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
        <Rectangle Fill="Red" Width="100" Height="100" Margin="10"/>
    </ItemsControl.Items>
</ItemsControl>

Answer 1

EntranceThemeTransition works on UWP. You can set IsStaggeringEnabled to true and get the animation even if the items are already there (your case).

<ItemsControl.ItemContainerTransitions>
    <TransitionCollection>
        <EntranceThemeTransition IsStaggeringEnabled="True"/>
    </TransitionCollection>
</ItemsControl.ItemContainerTransitions>