177 lines
5.1 KiB
Markdown
177 lines
5.1 KiB
Markdown
# Kotlin调用Jni的写法
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## 一、安装CMake和NDK
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在android studio的设置中安装Cmake，安装Cmake的时候注意cmake的版本。如果忘记CMake的版本，那么可以通过Android SDK Locatio目录中查看CMake的版本。如下图所示的CMake和NDK。
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## 二、创建工程
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选择一个带 Native C++ 支持的工程，如下图所示：
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## 三、配置 ndk 目录
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在文件 local.properties 中加入 ndk 的配置
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## 四、目录结构
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以下文件都是自动生成的
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## 五、配置模块 build.gradle
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```shell
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apply plugin: 'com.android.application'
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apply plugin: 'kotlin-android'
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apply plugin: 'kotlin-android-extensions'
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android {
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compileSdkVersion 29
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buildToolsVersion "29.0.2"
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defaultConfig {
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applicationId "com.lujianfei.androidjnicall"
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minSdkVersion 26
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targetSdkVersion 29
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versionCode 1
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versionName "1.0"
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testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
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externalNativeBuild {
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cmake {
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cppFlags ""
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}
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}
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}
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buildTypes {
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release {
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minifyEnabled false
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proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
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}
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}
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externalNativeBuild {
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cmake {
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path "src/main/cpp/CMakeLists.txt"
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version "3.10.2"
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}
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}
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}
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dependencies {
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implementation fileTree(dir: 'libs', include: ['*.jar'])
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implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
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implementation 'androidx.appcompat:appcompat:1.1.0'
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implementation 'androidx.core:core-ktx:1.2.0'
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implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
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testImplementation 'junit:junit:4.12'
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androidTestImplementation 'androidx.test.ext:junit:1.1.1'
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androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
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}
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```
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## 六、配置CMakeLists.txt和native-lib.cpp
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```
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# For more information about using CMake with Android Studio, read the
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# documentation: https://d.android.com/studio/projects/add-native-code.html
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# Sets the minimum version of CMake required to build the native library.
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cmake_minimum_required(VERSION 3.4.1)
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# Creates and names a library, sets it as either STATIC
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# or SHARED, and provides the relative paths to its source code.
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# You can define multiple libraries, and CMake builds them for you.
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# Gradle automatically packages shared libraries with your APK.
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add_library( # Sets the name of the library.
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native-lib
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# Sets the library as a shared library.
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SHARED
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# Provides a relative path to your source file(s).
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native-lib.cpp )
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# Searches for a specified prebuilt library and stores the path as a
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# variable. Because CMake includes system libraries in the search path by
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# default, you only need to specify the name of the public NDK library
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# you want to add. CMake verifies that the library exists before
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# completing its build.
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find_library( # Sets the name of the path variable.
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log-lib
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# Specifies the name of the NDK library that
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# you want CMake to locate.
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log )
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# Specifies libraries CMake should link to your target library. You
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# can link multiple libraries, such as libraries you define in this
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# build script, prebuilt third-party libraries, or system libraries.
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target_link_libraries( # Specifies the target library.
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native-lib
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# Links the target library to the log library
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# included in the NDK.
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${log-lib} )
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```
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```C++
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#include <jni.h>
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#include <string>
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extern "C" JNIEXPORT jstring JNICALL
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Java_com_lujianfei_androidjnicall_MainActivity_stringFromJNI(
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JNIEnv* env,
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jobject /* this */) {
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std::string hello = "Hello from C++";
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return env->NewStringUTF(hello.c_str());
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}
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```
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## 七、Activity调用
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```kotlin
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package com.lujianfei.androidjnicall
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import androidx.appcompat.app.AppCompatActivity
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import android.os.Bundle
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import kotlinx.android.synthetic.main.activity_main.*
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class MainActivity : AppCompatActivity() {
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override fun onCreate(savedInstanceState: Bundle?) {
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super.onCreate(savedInstanceState)
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setContentView(R.layout.activity_main)
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// Example of a call to a native method
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sample_text.text = stringFromJNI()
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}
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/**
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* A native method that is implemented by the 'native-lib' native library,
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* which is packaged with this application.
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*/
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external fun stringFromJNI(): String
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companion object {
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// Used to load the 'native-lib' library on application startup.
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init {
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System.loadLibrary("native-lib")
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}
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}
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}
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```
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