自己用NDK编写C++方法生成全平台so库

àì夳堔傛蜴生んèń 2023-06-26 12:08 2阅读 0赞

作者：谭东

软件环境：Windows+Android Studio+CMake

这里记录一下自己编写的简单C++方法，然后再编写JNI方法，最后通过CMake编译成全平台so库使用。

整个项目结构：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70][]

为了方便，我们可以用Android Studio的创建Native C++这个来创建项目，这样会自动给我们生成一个比较完善的目录结构。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 1][]

首先我们需要在项目的app/libs下新建一个include目录。这个目录的作用就是用来包含我们的C/C++库，当然也可以自己编写C/C++方法逻辑。例如这里我们放置了两个库JsonCpp库的libjson目录和自己写的libencrypt源码目录。一个完整的C/C++库源码一般包含.c/.cpp和.h文件。.c/.cpp为源码逻辑实现文件，.h为抽象的方法头文件。

我们看下自己写的encrypt.cpp文件：

#include "encrypt.h"
    #include <string>
    
    std::string getEncryptString(std::string text) {
        return "Encrypt:" + text + ":endl";
    }

头文件encrypt.h：

#ifndef ENCRYPTLIB_ENCRYPT_H
    #define ENCRYPTLIB_ENCRYPT_H
    #define _GLIBCXX_USE_CXX11_ABI 0
    
    #include <string>
    std::string getEncryptString(std::string text);
    
    #endif //ENCRYPTLIB_ENCRYPT_H

很简单，我就是想测试下so库调用我们的C++方法。

编写JNI方法，调用我们的libencrypt库的方法：

#include <jni.h>
    #include <string>
    #include "../../../libs/include/libencrypt/encrypt.h"
    
    extern "C" {
    using namespace std;
    
    //这个方法为定义的调用我们的libencrypt写的C++方法
    JNIEXPORT jstring JNICALL
    Java_com_google_encryptlib_MainActivity_getEncryptText(JNIEnv *env,
                                                           jobject, jstring text) {
        std::string license = getEncryptString(
                env->GetStringUTFChars(text, 0));//env->GetStringUTFChars(text, NULL)
        return env->NewStringUTF(license.c_str());
    }
    
    }

编写配置CMakeLists.txt：

# For more information about using CMake with Android Studio, read the
    # documentation: https://d.android.com/studio/projects/add-native-code.html
    
    # Sets the minimum version of CMake required to build the native library.
    
    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 them for you.
    # Gradle automatically packages shared libraries with your APK.
    set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)
    
    message("test ndk message")
    
    add_library( # Sets the name of the library.
            native-lib
    
            # Sets the library as a shared library.
            SHARED
    
            # Provides a relative path to your source file(s).
            native-lib.cpp)
    
    add_library( # Sets the name of the library.
            encrypt
    
            # Sets the library as a shared library.
            SHARED
    
            # Provides a relative path to your source file(s).
            ../../../libs/include/libencrypt/encrypt.cpp)
    
    #file(GLOB SRC_LIST "*.cpp" "../../../libs/include/libjson/*.cpp")
    #add_library( # Sets the name of the library.
    #        json
    #
    #        # Sets the library as a shared library.
    #        SHARED
    #
    #        # Provides a relative path to your source file(s).
    #        ${SRC_LIST})
    #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
    
    add_library(json
            SHARED
            IMPORTED)
    set_target_properties(json
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/${ANDROID_ABI}/libjson.so)
    message(${ANDROID_ABI})
    # 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.
            native-lib
            encrypt
            json
            # Links the target library to the log library
            # included in the NDK.
            ${log-lib})
    
    include_directories(libs/include)

build.gradle文件：

apply plugin: 'com.android.application'
    
    android {
        compileSdkVersion 28
        defaultConfig {
            applicationId "com.google.encryptlib"
            minSdkVersion 15
            targetSdkVersion 28
            versionCode 1
            versionName "1.0"
            testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
            externalNativeBuild {
                cmake {
                    cppFlags ""
                }
            }
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
            }
        }
        externalNativeBuild {
            cmake {
                path "src/main/cpp/CMakeLists.txt"
                version "3.10.2"
            }
        }
    }
    
    dependencies {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'com.android.support:appcompat-v7:28.0.0'
        implementation 'com.android.support.constraint:constraint-layout:1.1.3'
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'com.android.support.test:runner:1.0.2'
        androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191231201124673.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20191231201444854.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9mYW50YXN5LmJsb2cuY3Nkbi5uZXQ=,size_16,color_FFFFFF,t_70