JNI學(xué)習(xí)大綱

一、JNI編程入門

二、Android Studio中使用cmake開發(fā)JNI實戰(zhàn)

第一章節(jié)我們介紹了JNI的開發(fā)步驟，那這一章節(jié)我們就開始在Android Studio中實戰(zhàn)一下吧，Let's Start。

1. Android Studio中安裝CMake插件

• AS中菜單欄選擇Tools>SDK Manager
• 在Android SDK中選擇SDK Tools，安裝CMake和NDK。

2. JNI開發(fā)

2.1 編寫JNI代碼

在項目工程下的src/main創(chuàng)建cpp目錄，編寫native-lib.cpp（JNI代碼實現(xiàn)文件）和對應(yīng)的CMakeLists.txt（JNI代碼編譯配置）。文章來源地址http://www.zghlxwxcb.cn/news/detail-628628.html

// native-lib.cpp

#include <jni.h>
#include <android/log.h>
#include <string>

extern "C" JNIEXPORT jstring JNICALL
Java_com_jni_test_JNITestService_stringByJNI(
        JNIEnv *env, jobject /* this */) {
    std::string hello = "hello JNI from C++";
    return env->NewStringUTF(hello.c_str());
}

// CMakeLists.txt

# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.10.2)

# Declares and names the project.
project("jnitest")

# 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 them for you.
# Gradle automatically packages shared libraries with your APK.
set(project_root_dir ${CMAKE_CURRENT_SOURCE_DIR}/../../../..)
include_directories(${project_root_dir}/common)

add_library( 
    # Sets the name of the library.
    jnitest

    # Sets the library as a shared library.
    SHARED

    # Provides a relative path to your source file(s).
    native-lib.cpp
)

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries 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 this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( 
    # Specifies the target library.
    jnitest
    
    # Links the target library to the log library included in the NDK.
    ${log-lib}
)

2.2 gradle中編譯配置

android {
    ...
    defaultConfig {
        ...
        externalNativeBuild {
            // 設(shè)置生成so的arm架構(gòu)
            cmake {
                cppFlags ''
                abiFilters 'arm64-v8a'
            }
        }
    }

    externalNativeBuild {
        cmake {
            // 編譯
            path file('src/main/cpp/CMakeLists.txt')
            version '3.10.2'
        }
    }
}

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