本文使用将Cmake来集成和演示
一.给新建的普通工程加上cmake支持
在app/build.gradle
android{
defaultConfig{
....
externalNativeBuild {
cmake {
cppFlags "" //暂不了解具体用途
}
}
....
}
externalNativeBuild {
cmake {
path "CMakeLists.txt" //cmake文件的路径
}
}
}
添加完之后,你的app/build.gradle应当如下
android {
compileSdkVersion 28
buildToolsVersion "28.0.2"
defaultConfig {
applicationId "com.example.a1_opencv_helloworld"
minSdkVersion 15
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags ""
}
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
}
二.新建cpp文件
- 在app/main/cpp/include //存放头文件
- 在app/main/cpp //存放cpp或者.c
三.新建CMakeLists.txt
- 路径:app/CMakeLists.txt
- CMakeList.txt简单说明
# 指定cmke版本
cmake_minimum_required(VERSION 3.4.1)
add_library(native-lib
SHARED
src/main/cpp/Hello.c) #添加.c源文件
include_directories(src/main/cpp/include) #添加头文件的位置
target_link_libraries(native-lib
${
log-lib}) #选
四.在MainActivity中.加载so库
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
static {
System.loadLibrary("native-lib");
}
}
五.native层添加helloworld方法
- 在java层添加native方法
public class MainActivity extends AppCompatActivity {
public static final String TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d(TAG,getHello());
}
static {
//加载静态库,静态库的名字,再之前的CMakeList.txt指定
System.loadLibrary("native-lib");
}
//添加native方法
public native String getHello();
}
- 生成头文件有两种方式
- 直接在android studio 在方法上生成(鼠标放在方法上,alt+enter,出现create_function…)
- 使用javah -d (新版本jdk中 Java9-Java10已经不支持)
六.编写.h .c文件
Hello.h
#ifndef PRACTICLE_HELLO_H
#define PRACTICLE_HELLO_H
#include <android/log.h>
#include <jni.h>
JNIEXPORT jstring JNICALL
Java_com_example_a1_1opencv_1helloworld_MainActivity_getHello(JNIEnv *env, jobject instance);
#endif //PRACTICLE_HELLO_H
Hello.c
#include "Hello.h"
JNIEXPORT jstring JNICALL
Java_com_example_a1_1opencv_1helloworld_MainActivity_getHello(JNIEnv *env, jobject instance) {
return (*env)->NewStringUTF(env, "native hello world");
}
七.MainActivity修改
public class MainActivity extends AppCompatActivity {
public static final String TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView contentTv = findViewById(R.id.tv_content);
contentTv.setText(getHello());
}
static {
//加载静态库
System.loadLibrary("native-lib");
}
//添加native方法
public native String getHello();
}
运行效果:
code:https://github.com/HumorSmith/NDKPraticle/tree/master/1_helloworld