ChangeBasemap.xaml

<UserControl 
    x:Class="ArcGISRuntime.UWP.Samples.ChangeBasemap.ChangeBasemap"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:esri="using:Esri.ArcGISRuntime"
    xmlns:esriUI="using:Esri.ArcGISRuntime.UI.Controls" 
    mc:Ignorable="d" 
    d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <CommandBar>
            <AppBarButton Content="Basemaps">
                <AppBarButton.Flyout>
                    <Flyout>
                        <ListView x:Name="basemapChooser" SelectionChanged="OnBasemapListSelectionChanged"/>
                    </Flyout>
                </AppBarButton.Flyout>
            </AppBarButton>
        </CommandBar>
        <esriUI:MapView x:Name="MyMapView" Grid.Row="1"/>
    </Grid>
</UserControl>