Using null fallback also call onException listener

[TomasValenta]

Hi Sam,

again, I am not sure if it's a bug. When I use this:

Glide.with(context)
        .load(source) //source = null
        .fallback(R.drawable.empty)
        .listener(new RequestListener<GlideUrl, GlideDrawable>() {
            @Override
            public boolean onException(Exception e, GlideUrl model,
                                       Target<GlideDrawable> target, boolean isFirstResource) {
                return false;
            }

            @Override
            public boolean onResourceReady(GlideDrawable resource, GlideUrl model, Target<GlideDrawable> target,
                                           boolean isFromMemoryCache, boolean isFirstResource) {
                return false;
            }
        })
        .into(ImageView);

then fallback working well, but onException is also called. Is that right?

[sjudd]

I'm not totally sure what the expected behavior here is. I didn't change that in Glide 3.6 to keep the behavior the same.

I think it's ok. If fallbacks actually accepted full requests, you'd probably expect to be notified that your full load failed if you added a listener, even if one of the fallbacks eventually succeeds?

[TomasValenta]

If I understand correctly the idea of .fallback(int or Drawable), it's for handling null models?
Then it's not exception or it's?

Like in this table #268 .

[TWiStErRob]

I think onException should be called in correspondence with Target.onLoadFailed and showing .error().
I also think that null is not an exceptional case and load didn't "fail" because "null is a valid non-image" so it is expected behaviour, hence no exception. But since one of the listener methods should be called, the current behaviour may be OK. The above case can be distinguished by checking if there's an actual exception handed to onException.
However one may expect animated fallback in which case you would need onSuccess.

Sam's point is a weird case, I think the question is: Is listener for each target or for each load? and Do we consider fallback a separate load?
I could expect success to be called with fallback drawable on the main listener, but then onException was called before because we went to fallback. That is both methods were called :)

[sjudd]

This is hard one but I think I want to stick with the behavior we have. You can infer from the null model that onException was called because of a null model. I don't see a hugely compelling reason to change the behavior, particularly since users may currently be relying on it.