为什么这个简单的C＃UWP Win2D程序偶尔无法渲染图像

Question

Hi, my first post so please be gentle :)

I have written this simple C# UWP Win2D program that on occasions randomly fails to render the image on screen. The program runs without problems roughly 90% of the time, and as it should, it renders the image, oddly though every now and then it fails to render it.

When it fails, it still clears the canvas to the correct colour but it does not render anything else. The program seems to be running properly but when I place a break point on either the draw method or the update method a break does not occur.

'Break all' does break the program but it informs me "Your app has entered a break state, but there is no code to show because all threads were executing external code (typically system or framework code)"

I hope this explains the situation that I am currently facing, I have included the code that is causing this problem, hopefully someone more knowledgeable than me can help me find a remedy.

Here is my XAML code ...

<Page
    x:Class="TheGrid.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:TheGrid"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:canvas="using:Microsoft.Graphics.Canvas.UI.Xaml"
    mc:Ignorable="d" 
    Unloaded="Page_Unloaded">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <canvas:CanvasAnimatedControl 
            x:Name="canvas" 
            ClearColor="Bisque" Update="canvas_Update" Draw="canvas_Draw" CreateResources="canvas_CreateResources"
            />
    </Grid>
</Page>

And here is the C# code behind ...

public sealed partial class MainPage : Page
    {
        CanvasBitmap bitmap1;

        public MainPage()
        {
            this.InitializeComponent();
        }
        private void canvas_CreateResources(CanvasAnimatedControl sender, CanvasCreateResourcesEventArgs args)
        {
            args.TrackAsyncAction(Canvas_CreateResourcesAsync(sender).AsAsyncAction());
        }
        async Task Canvas_CreateResourcesAsync(CanvasAnimatedControl sender)
        {
            bitmap1 = await CanvasBitmap.LoadAsync(sender, "Assets/Images/testimage.png");
        }     
        private void canvas_Update(ICanvasAnimatedControl sender, CanvasAnimatedUpdateEventArgs args)
        {
            // Do stuff
        }
        private void canvas_Draw(ICanvasAnimatedControl sender, CanvasAnimatedDrawEventArgs args)
        {
            args.DrawingSession.DrawImage(bitmap1, 256, 256);
        }
        private void Page_Unloaded(object sender, RoutedEventArgs e)
        {
            this.canvas.RemoveFromVisualTree();
            this.canvas = null;
        }
    }

Thank you in advance for any help you may be able to offer, please let me know if more information is required.

Edit 1.) I have tried to simplify the problem by removing

args.TrackAsyncAction(Canvas_CreateResourcesAsync(sender).AsAsyncAction());

and

async Task Canvas_CreateResourcesAsync(CanvasAnimatedControl sender) { bitmap1 = await CanvasBitmap.LoadAsync(sender, "Assets/Images/testimage.png"); }

and replacing

args.DrawingSession.DrawImage(bitmap1, 256, 256);

with

args.DrawingSession.DrawCircle(256, 256, 128, Colors.Black, 16);

This seems to prevent the problem from occurring, so I can only presume that it is a problem with the async pattern that I am using.

Answer 1

I think the problem is in here

private void canvas_CreateResources(CanvasAnimatedControl sender, CanvasCreateResourcesEventArgs args)
    {
        args.TrackAsyncAction(Canvas_CreateResourcesAsync(sender).AsAsyncAction());
    }

When using async, my teacher told me to always use await and async function. Because this will cause problem.

Some reading source : https://msdn.microsoft.com/en-us/library/hh191443.aspx