MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Storage;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// The Blank Page item template is documented at https://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace ImageCropperTest
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();

            mainGrid.Loading += MainGrid_Loading;
        }

        private async void MainGrid_Loading(FrameworkElement sender, object args)
        {
            var file = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Assets\\Screenshot 2021-03-16 083652.png"));
            await imgCropper.LoadImageFromFile(file);
            this.imgCropper.AspectRatio = 1.0;
        }
    }
}