Task loading an image

Question

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I have an image called Cameleon.png sitting in Assert Folder.
int my MainPage_Loaded function I write something like this

C#

void MainPage_Loaded(object sender, RoutedEventArgs e)
{
     Task<writeablebitmap> imtask = GetImage();
     imtask.ContinueWith(t =>
     {
            WriteableBitmap writeableBmp = t.Result;
            ImageName.Source = writeableBmp;
     });
}

async Task<writeablebitmap> GetImage()
{
     string strImageName = string.Format("ms-appx:///Assets/Cameleon.png");
     Uri uri = new Uri(strImageName);

     WriteableBitmap bitMap = await new WriteableBitmap(1, 1).FromContent(uri);
        //    ImageName.Source = bitMap;
     return bitMap;
}

in my XAML file

XML

<Canvas>
 Image Canvas.Left="0" Canvas.Top="0" x:Name="ImageName"
</Canvas>

If I set ImageName.Source = bitMap; in my Task function it show the image, but if set in my MainPage_Loaded function it does NOT show.

What I am doing wrong?

Your help will be very much appriciated.

Best regards
Agha Khan

Posted 27-Mar-13 12:23pm

AghaKhan

Updated 27-Mar-13 15:06pm

Prasad Khandekar

v2

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Comments

Sergey Alexandrovich Kryukov 27-Mar-13 18:47pm

Please tag it: WPF.
—SA

AghaKhan 27-Mar-13 19:49pm

Update:
It looks like I can't add anything to my canvas.

I added this code in callback function as well as in my main function.
Rectangle r2 = new Rectangle();
r2.Height = 100;
r2.Width = 100;
r2.Fill = new SolidColorBrush(Colors.Red);

MyCanvas.Children.Add(r2);

I am unable to add any object to my canvas in my callback funtion. :-(

[no name] 27-Mar-13 20:35pm

It might be that GetImage is async but you are not waiting for the task to complete. Try using await and see if that helps.

AghaKhan 27-Mar-13 21:35pm

I NOT have to wait because ContinueWith means the Task is compleated. I posted the solution. It works now.

Prasad Khandekar 27-Mar-13 21:26pm

Hello AghaKhan,

Why not try it MSDN way.
void MainPage_Loaded(object sender, RoutedEventArgs e)
{
Task<writeablebitmap> imtask = GetImage();
WriteableBitmap writeableBmp = await imtask;
ImageName.Source = writeableBmp;
}

AghaKhan 27-Mar-13 23:56pm

Because it is sample and does not deal the real problem. In fact I want to write something on the image which (The way MSDN explained) will not help. I was not aware MSDN provided that solution but I told in my question that it works in a Task function as MSDN explained. The real solution is what I have provided.

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AghaKhan · Answer 1 · 2013-03-27T15:32:00

This is very unusual behavior, but there is a solution. There is need an extra parameter for ContinueWith call.
imtask.ContinueWith(t =>
{

if (t.IsFaulted == false)
{
WriteableBitmap writeableBmp = t.Result;
myImage.Source = writeableBmp;
}
}, TaskScheduler.FromCurrentSynchronizationContext());

Now it works fine.