Fit mode
If you are using the standard app without XAML customizings, the fit mode feature should work out of the box. However, when using a FlipView for displaying documents in your customized XAMLs, you must make sure to include the following binding to the FlipView's ItemTemplate so that the fit modes are properly applied.
<DataTemplate
...
xmlns:hs="using:UBIK.WinX.HotSpotting.Document">
...
<Grid.Resources>
...
<DataTemplate x:Key="FlipDocItemTemplate">
...
<hs:Document
...
FitMode="{Binding DocumentViewModel.FitMode}" />
</DataTemplate>
</Grid.Resources>
</DataTemplate>
...
xmlns:hs="using:UBIK.WinX.HotSpotting.Document">
...
<Grid.Resources>
...
<DataTemplate x:Key="FlipDocItemTemplate">
...
<hs:Document
...
FitMode="{Binding DocumentViewModel.FitMode}" />
</DataTemplate>
</Grid.Resources>
</DataTemplate>
FlipView
When using the FlipView control in your XAML code, it's better to enable UI virtualization. The difference in performance gets more obvious as the number of items in the FlipView increases. Here's how to enable it.
<FlipView
...
VirtualizingStackPanel.VirtualizationMode="Standard">
<Flipview.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</Flipview.ItemsPanel>
</FlipView>
...
VirtualizingStackPanel.VirtualizationMode="Standard">
<Flipview.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</Flipview.ItemsPanel>
</FlipView>
VirtualizingStackPanel.VirtualizationMode offers two possibilities: Standard & Recycling. In case you are interested, here are their differences.