Sharing Clojure code with an Android application

Base libraries

• android/clojure

  • Slimmed down version of Clojure 1.4 for Android
  • https://github.com/sattvik/clojure

• android/lein-droid

  • Build environment

  • https://github.com/alexander-yakushev/lein-droid

  • Add to profiles.clj

    {:user {:plugins [[lein-droid "0.1.0-beta1"]]} :android {:sdk-path "your android sdk path goes here"}}

  • Follow the Tutorial

• neko/neko

  • Clojurized version of some necessary Android classes (e.g. Context, Resource, Threading...)
  • Useful for native applications, not so much for cross-platform code

Steps

1. Motivation

   • Solve a problem in Clojure
   • Reuse the Clojure code in an Android application
   • Avoid forking the Clojure code for each target

2. Start with a vanilla Clojure project

   • No need for lein droid new ...

3. Create a Leiningen profile for each target in project.clj

; project.clj
(defproject factorial "0.1.0-SNAPSHOT"
  :description "A simple factorial library"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :source-paths ["src/common"]
  :java-source-paths ["src/java"]
  :profiles {:non-android {:dependencies [[org.clojure/clojure "1.4.0"]]
                     :source-paths ["src/non-android"]}
             :android {:dependencies [[android/clojure "1.4.0"]]
                       :source-paths ["src/android"]
                       :aot :all
                       :aot-exclude-ns ["clojure.parallel"]
                       :exclusions [[org.clojure/clojure]]}})

1. Run lein deps for each profile

   • lein with-profile android deps
   • lein with-profile non-android deps

2. Write beautiful Clojure code

   • Try to stay in src/common
   • Try to stay away from futures
   • Be kind to the stack

; src/common/factorial/factorial.clj
(ns factorial.factorial)

(defn factorial [n]
  (reduce * (range 1 (inc n))))`

1. [optional] Create a Java-friendly wrapper for Clojure code

;src/android/factorial/FactorialClient.clj
(ns factorial.FactorialClient
  (:use [factorial.factorial :only [factorial]])
  (:gen-class
   :methods [#^{:static true} [factorial [Long] Long]]))

(defn -factorial
  [n]
	  (factorial n))

1. Try it in the REPL
   • lein with-profile android ritz
   • lein with-profile android swank
   • jack-in won't work with a profile
   • ClassNotFoundException java.lang.ClassNotFoundException: clojure.lang.RT <- You didn't select a profile

(require 'factorial.factorial)
(factorial.factorial/factorial 10)

(require 'factorial.FactorialClient)
(factorial.FactorialClient/-factorial 10)

1. Create your jar file

   • lein with-profile android uberjar

2. Create an Android project

   • Copy the jar to libs
   • Add it to the Build Path (make sure to select the -standalone version)
   • Call it
   • Run the App
   • FOR GREAT GOOD!