很久没有写jni相关的项目了，闲下来复习以下，把jni项目的构建流程记录以下，为以后使用方便查阅。
1. 环境配置
1. 下载NDK
方法一：在官网手动下载
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选择想要下载的对应系统NDK版本，下载完成之后，解压到你ndk存放目录，这个目录后续配置环境变量需要用到
方法二：使用Android studio SDK Manager下载（Android studio 4.x）
点击Android studio 工具栏的
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File | Settings | Appearance & Behavior | System Settings | Android SDK或者Tool|SDK Manager打开SDK Manager 界面
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选择SDK Tools 条目，勾选NDK和CMake后点击apply按钮等待下载完即刻
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下载完成之后，ndk的位置在你的Android sdk目录下方，有一个ndk的文件夹。
2. 配置NDK
1.配置环境变量
打开高级环境变量控制
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配置环境变量，在环境变量的Path中添加ndk的路径
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我的路径是
D:\Android\SDK\ndk\21.3.6528147
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在cmd中输入ndk-build 出现以下结果证明配置成功
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2.已有项目中集成jni
1. 在Androidstudio中配置
打开已有项目，通过File|Project Structure|SDK location打开SDK和NDK配置界面，然后在ndk中配置你刚刚下载的NDK路径
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2. 在项目app目录下的build.gradle文件进行配置
apply plugin: 'com.android.application'
android {
compileSdkVersion 30
buildToolsVersion "30.0.1"
defaultConfig {
applicationId "com.marlon.testjni"
minSdkVersion 16
targetSdkVersion 30
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
// 增加cmake控制属性
externalNativeBuild {
cmake {
// 指定编译架构 可以省略
abiFilters 'arm64-v8a', 'armeabi-v7a', 'x86', 'x86_64'
// cpp 编译时的额外选项 可以省略
cppFlags ""
}
}
}
// 在android节点下
// 指定CMakeLists.txt路径
externalNativeBuild {
cmake {
// 在该文件种设置所要编写的c源码位置，以及编译后so文件的名字
path "src/main/jni/CMakeLists.txt"
// cmake版本 可以省略
version "3.10.2"
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: "libs", include: ["*.jar"])
implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.1'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}
2. 新建JNI folder用来放置C/C++文件和CMakeLists文件
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在app/src/main目录下将会创建一个jni文件夹。
3. 新建HelloJNI文件
在src/main/java文件夹下面创建HelloJNI.java文件
package com.marlon.testjni;
/**
* @author by marlon
* @date on 2020/9/13.
*/
public class HelloJNI {
static {
System.loadLibrary("native-lib");
}
public static native String helloJNI();
}
4.创建native-lib文件
在src/main/java 目录下创建native-lib.cpp
//
// Created by marlon on 2020/9/13.
//
#include
extern "C"
JNIEXPORT jstring JNICALL
Java_com_marlon_testjni_HelloJNI_helloJNI(JNIEnv *env, jclass clazz) {
// TODO: implement helloJNI()
return env->NewStringUTF("Hello From JNI!");
}
5. 创建CMakeLists文件
在src/main/jni文件中创建
# 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.
#指定CMake构建本地库时所需的最小版本
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.
add_library( # Sets the name of the library.
#将资源文件生成动态链接库（so文件）的库名称(文件名称：“lib" +设置的名称)
native-lib
# 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.
#将所有的add_library中的库链接起来，有多少个add_library成的库就将其添加到这里
#这个和add_library中的指定的so库名称一致
native-lib
# Links the target library to the log library
# included in the NDK.
${log-lib} )
3.使用
package com.marlon.testjni;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.text).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//在这里直接调用
String string = HelloJNI.helloJNI();
Toast.makeText(MainActivity.this, string, Toast.LENGTH_SHORT).show();
}
});
}
}
整个就是这样