The app crashes when using Skiasharp

Hi
I use this function for graphics.

using Plugin.Permissions;
using Plugin.Permissions.Abstractions;
using SkiaSharp;
using SkiaSharp.Views.Forms;
using System;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace Poetry
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class Page1 : ContentPage
    {
        SKBitmap bitmap;
        SKBitmap originalBitmap;

        public Page1(SKBitmap bitmap)
        {
            this.bitmap = bitmap;
            originalBitmap = bitmap;
            InitializeComponent();
            Graphics();
        }

        private void Canvas_PaintSurface(object sender, SKPaintSurfaceEventArgs e)
        {
            SKImageInfo info = e.Info;
            SKSurface surface = e.Surface;
            SKCanvas canvas = surface.Canvas;
            canvas.Clear();
            canvas.Scale((float)e.Info.Width / bitmap.Width);

            SKRect sk = new SKRect(0, 0, bitmap.Width, bitmap.Height);
            canvas.DrawBitmap(bitmap, sk, BitmapStretch.Uniform);
        }


        private void ButtonGenerated_Clicked(object sender, EventArgs e)
        {
            bitmap = originalBitmap;
            Graphics();
        }

        private void Graphics()
        {
            SKBitmap newBitmap = new SKBitmap(Convert.ToInt32(bitmap.Width), Convert.ToInt32(bitmap.Height));
            using (SKCanvas canvas = new SKCanvas(newBitmap))
            {
                canvas.Clear();
                Random rnd = new Random();
                int rotate = 90 * rnd.Next(1, 5);
                canvas.RotateDegrees(rotate, bitmap.Width / 2, bitmap.Height / 2);
                canvas.DrawBitmap(bitmap, 0, 0);
                canvas.RotateDegrees(-rotate, bitmap.Width / 2, bitmap.Height / 2);
            }

            bitmap = newBitmap;
            canvas.InvalidateSurface();

        }
    }
}

The code works well but when I call the function several times the application crashes, especially when the bitmap is large or when I use the touchPoints

How do I prevent app crashes.

Thank you in advance.