UWP - Set app launch window size

MainPage.xaml

<Page
    x:Class="UniversalAppTutorials.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:UniversalAppTutorials"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    >
    <StackPanel Padding="50">
    </StackPanel>
</Page>
MainPage.xaml.cs

using Windows.UI.Xaml.Controls;
using Windows.UI.ViewManagement;
using Windows.Foundation;


namespace UniversalAppTutorials
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();

            /*
                ApplicationView
                    Represents the active application view and
                    associated states and behaviors.

                PreferredLaunchViewSize
                    Gets or sets the size that the app launches with when the
                    ApplicationView.PreferredLaunchWindowingMode property is set
                    to PreferredLaunchViewSize, except in cases
                    where the system manages the window size directly.

                ApplicationViewWindowingMode
                    PreferredLaunchViewSize: When launched, the window is sized
                    as specified by the ApplicationView.PreferredLaunchViewSize property.
            */

            // Set the app window preferred launch view size
            ApplicationView.PreferredLaunchViewSize = new Size(Height = 300, Width = 450);

            // Set app window preferred launch windowing mode
            ApplicationView.PreferredLaunchWindowingMode = ApplicationViewWindowingMode.PreferredLaunchViewSize;
        }
    }
}