Loading image asynchronously in WPF using binding converter

Question

I have a Image control with binding settings like this:

<Image Stretch="Uniform" Source="{Binding Path=CurrentItem, Converter={StaticResource ImgConverter}, IsAsync=True}"/>

And the ImgConverter is:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            string uri = null;

            Compressor.Unzip((value as Zipfile));

            uri = string.Format("{0}{1}.jpg", Compressor.TempPath, value.ToString());

            return uri;

        }

The Compressor.Unzip(...) method does take some time. I set the binding IsAsync=True but it doesn't work(NOT on converter but only on path?). How can I handle this asynchronously?

Unfortunately the Binding.IsAsync property only affects the property getter, but not the binding converter. So you may consider to replace the converter by an additional view model property like CurrentImage which you can bind to asynchronously without converter. — Clemens
– Clemens, Commented Apr 15, 2014 at 6:34
Just add another property to the class where CurrentItem is defined. — Clemens
– Clemens, Commented Apr 15, 2014 at 7:03
@Clemens I used IsSynchronizedWithCurrentItem so the CurrentItem is not defined by myself. — Sean C.
– Sean C., Commented Apr 15, 2014 at 7:14

Clemens · Accepted Answer · 2014-04-15 07:33:17Z

1

Add a readonly Image property to your Zipfile class, and move the converter code to the property getter:

public class Zipfile
{
    ...

    public ImageSource Image
    {
        get
        {
            Compressor.Unzip(this);
            var uri = string.Format("{0}{1}.jpg", Compressor.TempPath, this.ToString());
            return new BitmapImage(new Uri(uri));
        }
    }
}

Then write your binding like this:

<Image Source="{Binding Path=CurrentItem.Image, IsAsync=True}"/>

answered Apr 15, 2014 at 7:33

Clemens

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3 Comments

Sean C. Over a year ago

Thanks. Although I met some thread problems, it is the best solution anyway.

Julien Over a year ago

@SeanC. how did you fix your thread problems? my images never show up

Sean C. Over a year ago

@Julien Like he said, do the trick in the getter. The converter will not work asynchronously. If that does not work for you, check if your image source has been triggered.

Reza ArabQaeni · Accepted Answer · 2014-04-15 05:18:16Z

0

Using Multibinding with two binding, First is self image control and second is your current binding, in converter you can call async your method to unzip the file and in callback you can set image path(refer to first binding); Also you can see this sample:

http://social.msdn.microsoft.com/Forums/en-US/7fc238ea-194e-4f29-bcbd-9a3d4bdb2180/async-loading-of-bitmapsource-in-value-converter?forum=wpf

answered Apr 15, 2014 at 5:18

Reza ArabQaeni

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1 Comment

Sean C. Over a year ago

It seems like this solution is to change the source property in converter. The source property is already bound. Will this twist the binding setting?

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