AvantX's J2ObjC: better interop primitives with ObjC world & access to Apple's APIs

Original Project site: http://j2objc.org

Overview

This is a fork of Google's J2Objc project that has has extentions that make it possible to write Java code that interacts with ObjC constructs including value types, C functions and blocks etc. Moreover, it comes with a relatively complete binding of the iOS system APIs so one can use this fork to write fully native iOS apps just in Java.

Interop Primitives

Interoperation with ObjC world is provided mostly in the form of unintrusive Java Annotations. Here we introduce some of the most commonly used ones:

• @Mapping("selector")

@Mapping annotation can be applied on instance method and class method, that modifies the output selectors of annotated methods. For instance, if we have the following annotated method declaration:

class Test {
	@Mapping("go")
	public static void test() {}
}

Then a method invocation like Test.test() will be translated into [Test go].

• @DotMapping("abc"), @GlobalConstant("abc"), @GlobalFunction("abc")

These annotations all modify the translation of a method call just like the @Mapping annotation. They will result in respectively: dot-style access for structs, referencing a global constant, and invoking global functions. A good place to get a grasp of all of them is CGRect.java

• @ExtensionMapping("abc")

ObjC's extension has no counterpart in Java so we use an extension syntax that's kind of like C#'s, where the first argument will be translated as the receiver. Example: NSCoderExtensions.java

• @Mapping("UITableView") for Class

@Mapping annotation can also be applied on a class declaration, which means the said class is mapped to some native class. This has two effects: 1. any class that has this annotation would not generate corresponding ObjC class headers or implementations as they should be provided elsewhere; 2. any method call(incl. instance instantiations etc) would resolve to the native class. For example,

@Mapping("UITableView")
class Hehe {
	@Mapping("goWithInt:")
	public static void test(Int x) {}
}

would not generate any implementation/header for class Hehe. And a call like Hehe.test(123) would be translated into [UITableView goWithInt:123].