【UWP】FlyoutのTextBox/ComboBoxが使えないときはAllowFocusOnInteraction="True"を設定しよう【AU必須】

最低ターゲットバージョン： Anniversary Update (1607)

<AppBarButton Label="購読グループを追加" Icon="Add" 
              AllowFocusOnInteraction="True"
              >
    <AppBarButton.Flyout>
        <Flyout>
            <StackPanel>
                <TextBox x:Name="SubscriptionGroupNameTextBox"
                    InputScope="Text"
                    />
                <Button Content="追加"
                    Command="{Binding AddSubscription}"
                    CommandParameter="{Binding ElementName=SubscriptionGroupNameTextBox, Path=Text}"
                    HorizontalAlignment="Right"
                    />
            </StackPanel>
        </Flyout>
    </AppBarButton.Flyout>
</AppBarButton>

参考

FrameworkElement.AllowFocusOnInteraction Property - Microsoft Docs

Can't enter enter text in TextBox control inside Flyout - stack overflow