Support react-native android

[realm]

Support react-native android

[alazier]

Steps added to the first comment

[emanuelez]

From what I can tell native modules on Android allow to use Java code, not C++ code. This probably means we will need to just define an API in Java that only includes native methods that are then implemented in the JNI level. It's an extra level of indirection... is this what was in your mind?

[alazier]

That's pretty much what I was thinking. The tricky part will be having our c++ objects communicate with react's c++ objects. If everything is just linked together in the ndk level then I could see this working out well.

[nhachicha]

They did mention a native module written in C++ in the doc https://github.com/facebook/react-native/blob/b86a6e3b44a63e92cf3a7976d2fa26c4bf412df1/ReactAndroid/src/main/java/com/facebook/react/bridge/NativeModule.java

{@link NativeModule}s whose implementation is written in C++

• must not provide any Java code (so they can be reused on other platforms), and instead should
• register themselves using {@link CxxModuleWrapper}.

I can't find this class they're mentioning in the Javadoc CxxModuleWrapper maybe we can use this wrapper to get hold of the context.

[alazier]

@nhachicha that sounds promising. But I also can't find anything remotely similar to that in the code base. Perhaps the comment is stale? Would it be possible to have a Java module that calls into our own c++ code throught jni? If so how do we set this up? I'm not even sure where to begin.

[nhachicha]

@alazier I'll give it a try once I finish this PR realm/realm-java#1809

[nhachicha]

@alazier I created a sample project https://github.com/nhachicha/ReactNativeWithJni to showcase how we can create a native react module that uses JNI.

with this approach we can just expose the current Java binding as a JS module (since we're already traversing Java to call C/C++). What could be interesting in terms of performance is to manage to grab the JSContextRef, I know you're using some kind of reflection in Objective-C to access this property since it's private. Does it make sense to send a PR or to ask FB to expose it via a method so third party libraries can inject their API?

[alazier]

Making progress here. All that is left now is chrome debugging and cleanup/proper support from react-native.