android - Fetch images with Callback in Picasso?

Question

I want to show a photo series with no gaps in-between the photos, where photos change in a regular interval. I realized Picasso initializes the ImageView before it starts downloading, and it always does that, no matter if I fetch() or not before calling into().

I fetch() to keep the gap between images small and also use .placeholder(R.color.black), but the gap is still visible, even when the image is loaded from memory.

My code looks like this

Picasso.with(getContext()).load(url).fetch();

then with a delay [which is currently fix and which I want to adjust dependent on network speed]

Picasso.with(getContext()).load(url).into(screenSurface);

I noticed that fetch() does not support any callback parameters and returns void, so it seems it's not possible for me to know when the cache is warmed.

Two questions:

1. Can I get noticed when an image is cached?
2. Is there maybe a different way to get rid of the breaks between the images and make them appear regularly.

[I know I could manually code this somehow, but if Picasso supports it, I'd like to use it.]

Answer 1

Based on the source, it looks like fetch does nothing upon completion, including notifying any potential listeners. Unfortunately, FetchAction isn't a public class, so you can't override this functionality either.

You can workaround this problem by using a custom Target subclass, like this:

Picasso.with(getContext()).load(url).into(new Target() {
    @Override public void onBitmapLoaded(Bitmap bitmap, Picasso.LoadedFrom from) {
        // cache is now warmed up
    }
    @Override public void onBitmapFailed(Drawable errorDrawable) { }
    @Override public void onPrepareLoad(Drawable placeHolderDrawable) { }
});