0.Introduction

Android apps are written in Java, Java have provide JNI(Java Native Interface) to call or be called by native applications and libraries written in other language such as C/C++ and assembly. Android provide NDK(Native Development Kit) to support native development in C/C++.

1.Installing NDK

The NDK can be download from Android Developer Website. After downloaded, we get an archive package, unpack it to whereever you want, and replace the full path with <NDK-Path> in below.

2.Use Mobile Print Project as an example

Step 0: Read /docs/OVERVIEW.html is helpful to understand the below steps.

Step 1: Create a project directory named "exampleProject", and a subdir named "jni", copy the C/C++ code to "jni"

exampleProject can be change whatever you want

Step 2: Create a file named "Android.mk", contains is likely as follow:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := PMX_MobilePrinter
LOCAL_SRC_FILES := test.c \
test1.c
LOCAL_C_INCLUDES := test.h
include $(BUILD_STATIC_LIBRARY)

The last line means, the output will be a static library, BUILD_SHARED_LIBRARY is for shared library.

3.Build for different platform

By default, the library is build for arm.Platforms are define in file "Application.mk" under jni directory, contains as follow:

APP_ABI := all

We need build for all platform, so the value after APP_ABI is all, which can be changed to armabi/armabi-v7a/x86/mips. Need to support different platform one time, just write as below, split with blank space.

APP_ABI := armabi armabi-v7a x86 mips

4.Build the library

Go to the "jni", run build command /ndk-build in Terminal(Mac/Linux)/CMD(Windows). Then you will find our library in exampleProject/obj/local/<PlatformName>/libPMX_MobilePrinter.a. Build shared library is placed in exampleProject/libs/<PlatformName>/libPMX_MobilePrinter.so.