Why does extented layout on landscape mode shows half black screen in Xamarin Forms?

Question

I have two Views and two content pages, in one I have them arrange vertically and it's shown when the device is on portrait mode, something like this:

<StackLayout>
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="*"/>
                    <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>

                <views:ScoresView Grid.Row="0"/>
                <views:CategoriesView Grid.Row="1"/>

            </Grid>
        </StackLayout>

And the other content page for landscape mode

<StackLayout>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>

            <views:ScoresView Grid.Column="0"/>
            <views:CategoriesView Grid.Column="1"/>
        </Grid>
    </StackLayout>

I wanted it to look like this:

but looks like this:

This is how I'm calling one or the other when the rotation is shifted

protected override void OnSizeAllocated(double width, double height)
        {
            base.OnSizeAllocated(width, height);
            if (width > height)
            {
                //device is landscape
                App.Current.MainPage = new CategoriesLands();
            }
            else
            {
                //device is portrait (or square)
            }
        }

Answer 1

You could change the StackLayout StackOrientation property to achieve the effect.

<StackLayout x:Name="outerStack">       
     <views:ScoresView HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand"/>
     <views:CategoriesView HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand"/>
</StackLayout>

in the behind code:

private double width;
private double height;
protected override void OnSizeAllocated(double width, double height)
    {
        base.OnSizeAllocated(width, height);
        if (width != this.width || height != this.height)
        {
            this.width = width;
            this.height = height;
            if (width > height)
            {
                outerStack.Orientation = StackOrientation.Horizontal;
            }
            else
            {
                outerStack.Orientation = StackOrientation.Vertical;
            }
        }
    }

the more you could refer to this.