Create a pluggable JSON parsing module

[airbnb]

Create a pluggable JSON parsing module

[0legg]

Few days ago there was JSON spec created for bodymovin, and I'm working on bringing it to JSON Schema — so it'll be possible in the future autogenerate parser source code.

[felipecsl]

our model classes are still somewhat coupled to the JSON structure, but over time we should decouple them as much as possible in a way that makes us input format agnostic. All you need is a converter that takes an InputStream and outputs a LottieComposition

[gpeal]

@felipecsl

[felipecsl]

This is gonna require a fair amount of work to decouple JSONObject from LottieComposition.
I think first we should flatten the package structure into just com.airbnb.lottie so you can keep everything package private and prevent from leaking classes to users (and avoid the @RestrictTo annotation).
@gpeal if you agree with that, I could go ahead and break it down into multiple artifacts (java libs) for model, layers, animation, etc. That way we can keep each module small while maintaining everything under a single package.
That's sort of a pre-requisite change in order for us to be able to have pluggable json parsing implementations. What do you think?

[gpeal]

@subtleGradient suggested using FlatBuffer. Tracking progress here.

[gpeal]

@felipecsl That sounds like a good plan. Having better scope protection is also definitely good.

[felipecsl]

Alright, I'll start going down this path then :)

[pdenise708]

K p

[ZacSweers]

@felipecsl did you start this? If not I'd like to contribute. I think the core of this is that a composition should be constructable via some conventional way (maybe a builder?). The default could basically be the current JSONObject implementations, with maybe some batteries-included optional artifacts that do it with gson/moshi/etc.

[felipecsl]

@hzsweers nope, I was waiting for @gpeal to finish some major JSON parsing refactoring that he had underway. AFAIK the plan was to move the current implementation to a streaming JsonReader which should be more memory efficient. Not sure what's the status of that change though, @gpeal can help clarify

[gpeal]

@felipecsl @hzsweers I spent quite a long time working on the JsonReader refactor which would have been a good end-all solution to this since it's strictly n time. However, there were some issues with the way the json was formatted that made it almost impossible to do proper parsing when only reading the json beginning to end linearly. Here is my WIP if you're interested: d7227b3

I synced up with Hernan on bodymovin about it and he made a few changes to the json that would make it more feasible:
airbnb/lottie-web@6ed7b0f
airbnb/lottie-web@18201cb

I want to give it another try but it would break compatibility with older versions so maybe splitting json parsing into a module and using the new one if you have a new animation would be a good idea and then we can drop support for older versions eventually.

@felipecsl Do you want to take another stab at this?

[felipecsl]

Sounds good to me, thanks for clarifying @gpeal.
@hzsweers I think we're on the same page about how it should work. I can probably work on it this week, we can sync offline on the details. How does that sound?

[gpeal]

For reference, the longest and most complex json file, LottieLogo2.json (90kb) takes about 30ms to parse.

[ZacSweers]

sounds good

[felipecsl]

Alright let me explain the rest of the changes I have in mind for this issue so I can get input from you guys before sending the PR:
We'd have a new class called Lottie responsible for initializing the library state. It would have a builder where we could specific the desired Converter implementation to use (similar to how Retrofit works). We could also use this in the future to configure other settings for the library:

Lottie lottie = new Lotite.Builder()
  .converter(new DefaultJsonConverter())
  .build()

Then, we'd need to use this lottie object when loading animations so it knows which Converter implementation to use:

animationView.setAnimation(lottie, "hello-world.json");

We'd also move the current LottieComposition.Factory#fromJson(), etc. APIs to Lottie#fromJson(). That'd be the entry point for most operations.

LottieAnimationView would use a default implementation of Lottie when app:lottie_fileName is used via XML since we wouldn't have the chance to initialize the Lottie object properly. We'll have to find a way to cover that scenario by maybe initializing it via a singleton.

Finally, the different Converter implementations would live in separate artifacts (also Android libraries). In order to use Lottie, you'd have to depend on the correct artifact, for example:

  compile 'com.airbnb.android:lottie-converter-default:version'

The lottie-converter-default artifact depends on lottie so it would get the dependency transitively.

What do you guys think?

[0legg]

Looks good to me; but it's still unclear how will you manage model and logic separation. Also, it's interesting, whether it's possible to parse JSON with databinding; and to provide model automatically from JSON Schema. I wish I had enough time to contribute lot of stuff here

[fabionuno]

There is any advantage to use this new Lottie class as a parameter of setAnimation method and not as a parameter of LottieAnimationView's constructor?
Using as a method parameter is useful if we need to use different JSON loaders with same LottieAnimationView instance, but i don't see a situation where this will occur, and I need to define Lottie as a member variable of my class to use it every time I call setAnimation.

A setSingletonInstance method could be created, like Picasso, to configure the default behavior of Lottie and use this singleton when a custom one is not specified in LottieAnimationView constructor.

This will help when instantiating LottieAnimationView from XML as you suggested.

[gpeal]

@felipecsl I like the overall approach. What do you think about Lottie including the default parser as a transitive dependency so that a) LottieAnimationView can create the default one and b) users don't have to add a second dependency especially when, as of now, there is only one option

[felipecsl]

@gpeal that's not possible because it would cause a circular dependency.
@fabionuno we can't add Lottie as a constructor paramterer to LottieAnimationView because it needs to be instantiated from the XML

[fabionuno]

@felipecsl The idea was to have a new constructor with Lottie as a parameter and when missing get the singleton instance, however in a situation where I declare the LottieAnimationView in XML but load the JSON animation programmatically, have it as parameter of the method setAnimation is a better option.

[gpeal]

@fabionuno Adding View constructors is pretty unconventional. We could also add something like what RV does with LayoutManager: https://developer.android.com/reference/android/support/v7/widget/RecyclerView.html#attr_android.support.v7.recyclerview:layoutManager

[felipecsl]

Should we close this issue? Not sure we're still planning to do anything else for this.

[gpeal]

@felipecsl Let's close this for now.