To have a CustomPage instead of default Page for base of all pages in the application.

Question

Instead of having the base Page for all the xaml page files, I need to have my CustomPage.xaml. I have created a CustomPage and had it as a base of my SettingsPage.xaml. It compiles successfully but throws a warning. Please check the code follows,

using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
namespace CustomPageTest
{
    public partial class CustomPage : Page
    {
        public CustomPage()
        {
            this.InitializeComponent();
            this.Loaded += CustomPage_Loaded;
        }
        private void CustomPage_Loaded(object sender, RoutedEventArgs e)
        {
            if (MyTextBlock != null)
            {
            }
        }
    }
}

<Page
    x:Class="CustomPageTest.CustomPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid>
        <Frame x:Name="Frame" />
        <TextBlock x:Name="MyTextBlock" Text="Hello" />
    </Grid>
</Page>

namespace CustomPageTest
{
    public sealed partial class SettingsPage : CustomPage
    {
        public SettingsPage()
        {
            this.InitializeComponent();
        }
    }
}

<local:CustomPage
    x:Class="CustomPageTest.SettingsPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:CustomPageTest"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid>
    </Grid>
</local:CustomPage>

In the CustomPage_Loaded event, the MyTextBox property is null.

Please check the warning thrown