Johan Karlsson: Images in a ListView on iOS
Since Xamarin Forms Listview now reuses cells in iOS (as it should) one small piece was overlooked. The reused cells now displays previously displayed images for a short while until the new image is downloaded.
This behavior is mitigated by a cache, so once an image is loaded it’s set instantly the next time the cell is displayed.
I’ve also filed a bug with a sample project available at https://bugzilla.xamarin.com/show_bug.cgi?id=28628 and the sample project to visualize the issue at here.
There are a number of ways around this.
Suggestion one – half-way around
public class CustomImageRenderer : ImageRenderer
protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
if ((sender as Image).IsLoading)
// The image will be reset in base if there is one already in the cache.
// If it isn‘t already loaded we don‘t want to display the previous image
// This is however called each time a cell comes into view so it can‘t
// be used for opacity fading or likewise...
// This should be handled by the code in the ImageRenderer
Control.Image = null;
Suggestion two – wrap it
Wrap your image in a custom control and handle all the loading and caching yourself.
Suggestion three – rewrite it
Write your own Image-renderer from scratch to take into account when an image is fetched from the cache or not to enable a nice fade in. This is what I hope will come out of the bug report.