JNI编程基础（二）——Android Studio NDK开发

由于笔者目前的工作是Android开发，所以在JNI开发系列博客中穿插一篇AndroidStudio NDK开发介绍。

随着Android Studio 2.2的推出，Android Studio的NDK开发支持Cmake和ndk-build两种方式，简化了Android Studio上NDK开发流程，提升了开发效率。接下来就介绍下两种开发方式。

1. CMake

CMake是一个跨平台的编译（安装）工具，支持通过用较为简单的语言来描述编译（安装）过程，最后输出适配不同平台的makefile货project文件。Android Studio通过引入CMake来简化JNI函数的编译。接下来通过一个例子来展示基于CMake的Android Studio NDK开发：

1. 创建一个Android工程，创建时勾选支持c++开发

创建完成后会看到在工程中会有一个c++目录，与Java目录同级

2. 在c++目录下创建两个文件：jni_lic.cpp/h。

3.在c++目录下创建CMakeLists.txt文件，文件内容如下：

# Sets the minimum version of CMake required to build the native# library. You should either keep the default value or only pass a# value of 3.4.0 or lower.cmake_minimum_required(VERSION 3.4.1)# Creates and names a library, sets it as either STATIC# or SHARED, and provides the relative paths to its source code.# You can define multiple libraries, and CMake builds it for you.# Gradle automatically packages shared libraries with your APK.AUX_SOURCE_DIRECTORY(./src/main/cpp DIR_SRCS)add_library( # Sets the name of the library.            jni-lib             # Sets the library as a shared library.             SHARED             # Provides a relative path to your source file(s).             # Associated headers in the same location as their source             # file are automatically included.             ${DIR_SRCS}             )include_directories(src/main/cpp/)# Searches for a specified prebuilt library and stores the path as a# variable. Because system libraries are included in the search path by# default, you only need to specify the name of the public NDK library# you want to add. CMake verifies that the library exists before# completing its build.find_library( # Sets the name of the path variable.              log-lib              # Specifies the name of the NDK library that              # you want CMake to locate.              log )# Specifies libraries CMake should link to your target library. You# can link multiple libraries, such as libraries you define in the# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.                       jni-lib                       # Links the target library to the log library                       # included in the NDK.                       ${log-lib} )

4. 在gradle中加入相关配置

android {    compileSdkVersion 24    buildToolsVersion "24.0.3"    defaultConfig {        applicationId "com.asia.jni"        minSdkVersion 15        targetSdkVersion 24        versionCode 1        versionName "1.0"        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"        externalNativeBuild {            cmake {                cppFlags ""            }        }    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'        }    }    externalNativeBuild {        cmake {            path "src/cpp/CMakeLists.txt"        }    }}

5.配置NDK路径

file->project structure->SDK Location:

如果没有安装NDK，可以通过SDK Manager安装。

6. JNI函数开发

这部分可以参考上一篇博客：JNI编程基础（一）

NDK-BUILD

ndk-build方式与cmake方式类似，只需要将cmake文件改写为Android.mk和Appliction.mk文件。在CMakeLists.txt加载的位置将CMakeLists.txt替换为Android.mk即可

1.Android.mk

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)APP_ABI := allLOCAL_MODULE    := jni-libLOCAL_CPPFLAGS     := -O0 -D_UNICODE -DUNICODE -DUSE_DUMP -Wno-error=format-securityLOCAL_CPP_EXTENSION := .cppLOCAL_LDLIBS    := -lm -llog -lzLOCAL_SHORT_COMMANDS := trueINC_DIRS = -I$(LOCAL_PATH)/src/cppLOCAL_CPPFLAGS += $(INC_DIRS)LOCAL_SRC_FILES    := \    jni_lib.cpp    \    \LOCAL_SHARED_LIBRARIES += libandroid_runtimeinclude $(BUILD_SHARED_LIBRARY)

2.Application.mk

APP_ABI := allNDK_TOOLCHAIN_VERSION := clangAPP_SHORT_COMMANDS      := trueAPP_STL := stlport_staticAPP_CPPFLAGS := -std=gnu++11 -D__STDC_LIMIT_MACROS

3.替换gradle的配置中cmake

//    externalNativeBuild{//        cmake{//            path file("src/main//CMakeLists.txt")//        }//    }    externalNativeBuild{        ndkBuild{            path file("src/main/cpp/Android.mk")        }    }