由于筆者目前的工作是Android開發，所以在JNI開發系列博客中穿插一篇AndroidStudio NDK開發介紹。

隨著Android Studio 2.2的推出，Android Studio的NDK開發支持Cmake和ndk-build兩種方式，簡化了Android Studio上NDK開發流程，提升了開發效率。接下來就介紹下兩種開發方式。

1. CMake

CMake是一個跨平臺的編譯（安裝）工具，支持通過用較為簡單的語言來描述編譯（安裝）過程，最后輸出適配不同平臺的makefile貨project文件。Android Studio通過引入CMake來簡化JNI函數的編譯。接下來通過一個例子來展示基于CMake的Android Studio NDK開發：

1. 創建一個Android工程，創建時勾選支持c++開發

創建完成后會看到在工程中會有一個c++目錄，與Java目錄同級

2. 在c++目錄下創建兩個文件：jni_lic.cpp/h。

3.在c++目錄下創建CMakeLists.txt文件，文件內容如下：

# 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中加入相關配置

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

5.配置NDK路徑

file->project structure->SDK Location:

如果沒有安裝NDK，可以通過SDK Manager安裝。

6. JNI函數開發

這部分可以參考上一篇博客：JNI編程基礎（一）

NDK-BUILD

ndk-build方式與cmake方式類似，只需要將cmake文件改寫為Android.mk和Appliction.mk文件。在CMakeLists.txt加載的位置將CMakeLists.txt替換為Android.mk即可

1.Android.mk

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS) APP_ABI := allLOCAL_MODULE := jni-lib LOCAL_CPPFLAGS := -O0 -D_UNICODE -DUNICODE -DUSE_DUMP -Wno-error=format-security LOCAL_CPP_EXTENSION := .cpp LOCAL_LDLIBS := -lm -llog -lz LOCAL_SHORT_COMMANDS := true INC_DIRS = -I$(LOCAL_PATH)/src/cpp LOCAL_CPPFLAGS += $(INC_DIRS)LOCAL_SRC_FILES := \jni_lib.cpp \ \LOCAL_SHARED_LIBRARIES += libandroid_runtimeinclude $(BUILD_SHARED_LIBRARY)

2.Application.mk

APP_ABI := all NDK_TOOLCHAIN_VERSION := clang APP_SHORT_COMMANDS := true APP_STL := stlport_static APP_CPPFLAGS := -std=gnu++11 -D__STDC_LIMIT_MACROS

3.替換gradle的配置中cmake

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

總結

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