XamlRenderingBackgroundTask snippets

RenderCode

internal class GraphTile
    {
		public static Task CreateTileGraphAsync(Data data, int width, int height, string filename)
		{
			return RenderAndSaveToFileAsync(GetVisual(data, width, height), (uint)width, (uint)height, filename);
		}
		public static Task CreateTileGraphAsync(Data data, int width, int height, IRandomAccessStream stream)
		{
			return RenderAndSaveToStreamAsync(GetVisual(data, width, height), (uint)width, (uint)height, stream);
		}
		public static Windows.UI.Xaml.UIElement GetVisual(Data data, int width, int height)
		{
			return GetVisual(data, width, height, new SolidColorBrush(Colors.White));
		}
		public static Windows.UI.Xaml.UIElement GetVisual(Data data, int width, int height, Brush pathbrush)
		{
		  //TODO: Create you XAML UI here and return root element
		  return new Border() { Width = width, Height = height, Background = pathbrush };

		}
		private static async Task RenderAndSaveToFileAsync(UIElement element, UInt32 width, UInt32 height, string filename)
		{
			var resultStorageFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;
			var outputStorageFile = await resultStorageFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
			using (var outputFileStream = await outputStorageFile.OpenAsync(FileAccessMode.ReadWrite))
			{
				await RenderAndSaveToStreamAsync(element, width, height, outputFileStream);
			}
		}
		private static async Task RenderAndSaveToStreamAsync(UIElement element, UInt32 width, UInt32 height, IRandomAccessStream outputFileStream)
		{
			RenderTargetBitmap rtb = new RenderTargetBitmap();
			await rtb.RenderAsync(element, (int)width, (int)height);
			var pixelBuffer = await rtb.GetPixelsAsync();
			var dataReader = Windows.Storage.Streams.DataReader.FromBuffer(pixelBuffer);
			var pixelWidth = (uint)rtb.PixelWidth;
			var pixelHeight = (uint)rtb.PixelHeight;
			rtb = null;

			byte[] buffer = new byte[pixelBuffer.Length];
			dataReader.ReadBytes(buffer);
			var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, outputFileStream);
			encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied, pixelWidth, pixelHeight, 96, 96, buffer);
			await encoder.FlushAsync();
			buffer = null;
			//await outputFileStream.FlushAsync();
		}
		public static async Task<WriteableBitmap> RenderMiniToWritableBitmap(Data data, UInt32 width, UInt32 height)
		{
			RenderTargetBitmap rtb = new RenderTargetBitmap();
			var element = GetMiniVisual(data, (int)width, (int)height, new SolidColorBrush(Colors.White));
			await rtb.RenderAsync(element, (int)width, (int)height);
			var wb = new WriteableBitmap((int)width, (int)height);

			IBuffer pixelBuffer = await rtb.GetPixelsAsync();
			using (var stream = new InMemoryRandomAccessStream())
			{
				var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream);
				encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore,
					(uint)rtb.PixelWidth, (uint)rtb.PixelHeight, 96, 96, pixelBuffer.ToArray());

				await encoder.FlushAsync();
				stream.Seek(0);
				wb.SetSource(stream);
			}
			// Redraw the WriteableBitmap
			wb.Invalidate();

			return wb;
		}

TaskCode

	public sealed class UpdateTileHandler : XamlRenderingBackgroundTask
	{
		BackgroundTaskDeferral _deferral;
		protected async override void OnRun(IBackgroundTaskInstance taskInstance)
		{
			_deferral = taskInstance.GetDeferral();
			base.OnRun(taskInstance);
			Update(taskInstance);
		}
		private async void Update(IBackgroundTaskInstance taskInstance)
		{
			string filename = "tile.png";
			await GraphTile.CreateTileGraphAsync(null, 310, 150, filename);
			//todo: Update tile
		}
	}