I am importing headers from an existing project for a port to Android-NDK. In a few cases, there are enums defined in the native headers which I would like to use from the Java layer. How can one go about doing that?
Ideally, I’d like to just expose the constants to the Java layer somehow, but I don’t see a way to do that.
The most obvious possibility is to doubly-define the enums in both Java and C++. However, the existing headers a) have no explicit numbering, b) have elements which are #ifdef’ed, and c) are shared with existing projects through SVN Externals. Therefore, doubly-defining the enums seems substantially more brittle than even the typical case.
The next idea is to use some build-time code-gen to create the enum in Java based on the pre-processed header — possibly just as integer constants rather than a Java enum?
The third and most-nebulous idea I have is to define the enum in Java, pass those objects to the JNI glue, and have it compare against the some invocation of FindClass(), GetStaticFieldID(), and GetStaticObjectField(); then have the JNI glue re-map those to the native enum. That all seems inefficient, though.
Suggestions?
I would make a completely independent set of Java enums, and map between them at the JNI level where you have both available. Make sure to run javah on the enum classes so you get some #defines for their ordinals.