wpf window size fix.

        public MainWindow()
        {
            //something...
            ///////////////
            ///////////////
            //add below
            this.Navigated += MainWindow_Navigated;
            this.ResizeMode = ResizeMode.CanResizeWithGrip;
        }
        protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo)
        {
            double aspectRatio = (1440.0 / 810.0);
            if (sizeInfo.WidthChanged)
            {
                this.Width = sizeInfo.NewSize.Height * aspectRatio;
            }
            else
            {
                this.Height = sizeInfo.NewSize.Width * aspectRatio;
            }

            base.OnRenderSizeChanged(sizeInfo);

            FixSize(sizeInfo.NewSize);
        }

        private void MainWindow_Navigated(object sender, NavigationEventArgs e)
        {
            FixSize(this.RenderSize);
        }

        private void FixSize(Size size)
        {
            double perX = size.Width / 1440.0;
            double perY = size.Height / 810.0;

            var content = this.NavigationService.Content;


            if (content != null && content is System.Windows.Controls.Page)
                (content as System.Windows.Controls.Page).LayoutTransform = new System.Windows.Media.ScaleTransform() { CenterX = .5, CenterY = .5, ScaleX = perX, ScaleY = perY };
        }