Add programmatic view support

[elihart]

@gpeal @ngsilverman

[elihart]

I will follow up later with a processor change to create a view type when one isn't explicity defined

[ngsilverman]

class ViewTypeManager {
  private final Map<Class<? extends EpoxyModel>, int> viewTypeMap = new HashMap<>();

  public int getViewType(EpoxyModel model) {
    Class<? extends EpoxyModel> modelClass = model.getClass();
    if (!viewTypeMap.contains(modelClass)) {
      int viewType = -viewTypeMap.size()-1;
      viewTypeMap.put(modelClass, viewType);
      return viewType;
    } else {
      return viewTypeMap.get(modelClass);
    }
  }
}

How about using a singleton to generate unique View types for every model class?

[elihart]

@ngsilverman thanks for looking! yep, something like that would definitely work. The main issue is this can't work across multiple modules. They would instantly clash since they all start at -1 and go down. By using a hash we at least have a pretty high chance of not having a collision. The other thing I considered is that a hash of the class name is reproducible, whereas something like this could arbitrarily result in a different value if more model classes are added/deleted/implementation changes or whatever. it seems useful to have a fairly reproducible viewtype so if people do have a collision it is reproducible.

On the other hand, if we did it this way we could basically rule out library model sharing because they would clash. That might be safer than saying it probably won't be a hash collision. I think I can add debug checking for models with a view type collision being used in the same adapter at runtime though, and alert the user to use a manual id in that case, so that takes the risk away from random unknown collisions.

What do you think?

[ngsilverman]

I should have clarified: My suggestion is to use the singleton at runtime, not during the annotation processing. Hence it should work across modules.

[elihart]

oh wow, brilliant! I think that could be perfect. I had too much tunnel vision on accomplishing this during processing, but your idea is much more simple and elegant