基于Android studio3.6的JNI教程之opencv

基本环境：

Android studio3.6

NDK:r14b（尽量使用该版本）

OpenCV3.4.1 android sdk

 

(1)新建工程OpenCVDemo，选择，一定要选择Native c++类型，最后要选c++14支持。

(2)File->Project Structure->SDK Location,设置这3个路径，NDK选择r14b。

(3)任意找一张图片，复制到res/drawable。

(4)修改布局文件res/layout/ activity_main.xml

(5)修改java文件，app/src/main/java/ com.example.opencvdemo/ MainActivity

主要修改包括修改

继承OnClickListener类，

修改onCreate方法

增加c++的接口函数，getEdge

实现点击按钮的方法，

整体代码如下，

package com.example.opencvdemo;
import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = findViewById(R.id.imageView);
        findViewById(R.id.show).setOnClickListener(this);
        findViewById(R.id.process).setOnClickListener(this);
    }
    
    //获得Canny边缘
    public native void getEdge(Object bitmap);
    private ImageView imageView;
    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.show) {
            Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);
            imageView.setImageBitmap(bitmap);
        } else {
            Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);
            getEdge(bitmap);
            imageView.setImageBitmap(bitmap);
        }
    }
}

(6)Terminal下进入app\src\main\java这一层目录，执行，

javah com.example.opencvdemo.MainActivity

将生成的com_example_opencvdemo_MainActivity.h，剪切到app/src/main/cpp目录下。

(7)修改app/src/main/cpp下面的native-lib.cpp，主要通过c++实现getEdge方法，主要代码如下，

#include 
#include 
#include "com_example_opencvdemo_MainActivity.h"
#include 
#include 
using namespace cv;
extern "C"
JNIEXPORT void JNICALL
Java_com_example_opencvdemo_MainActivity_getEdge(JNIEnv *env, jobject obj, jobject bitmap){
    // TODO: implement getEdge()
    AndroidBitmapinfo info;
    void *pixels;
    CV_Assert(AndroidBitmap_getInfo(env, bitmap, &info) >= 0);
    CV_Assert(info.fORMat == ANDROID_BITMAP_FORMAT_RGBA_8888 ||
              info.format == ANDROID_BITMAP_FORMAT_RGB_565);
    CV_Assert(AndroidBitmap_lockPixels(env, bitmap, &pixels) >= 0);
    CV_Assert(pixels);
    if (info.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
        Mat temp(info.height, info.width, CV_8UC4, pixels);
        Mat gray;
        cvtColor(temp, gray, COLOR_RGBA2GRAY);
        Canny(gray, gray, 125, 225);
        cvtColor(gray, temp, COLOR_GRAY2RGBA);
    } else {
        Mat temp(info.height, info.width, CV_8UC2, pixels);
        Mat gray;
        cvtColor(temp, gray, COLOR_RGB2GRAY);
        Canny(gray, gray, 125, 225);
        cvtColor(gray, temp, COLOR_GRAY2RGB);
    }
    AndroidBitmap_unlockPixels(env, bitmap);
}

(8)修改CMakeLists.txt

包括增加opencv包含路径，增加opencv链接，增加目标库的链接（OpenCV_LIBS和jnigraphics）

全部代码如下，

# 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.
#设置OpenCV-android-sdk路径
set( OpenCV_DIR E:/Android/OpenCV-android-sdk/sdk/native/jni )
find_package(OpenCV REQUIRED )
if(OpenCV_FOUND)
    include_directories(${OpenCV_INCLUDE_DIRS})
    message(STATUS "OpenCV library status:")
    message(STATUS "    version: ${OpenCV_VERSION}")
    message(STATUS "    libraries: ${OpenCV_LIBS}")
    message(STATUS "    include path: ${OpenCV_INCLUDE_DIRS}")
else(OpenCV_FOUND)
    message(FATAL_ERROR "OpenCV library not found")
endif(OpenCV_FOUND)
set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a")
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 )
# 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
                       ${OpenCV_LIBS}
                       jnigraphics
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

(9)修改app/build.gradle

主要增加cmake的cppFlags，arguments

全部代码如下，

apply plugin: 'com.android.application'
android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"
    defaultConfig {
        applicationId "com.example.opencvdemo"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++14 -frtti -fexceptions"
                arguments '-DANDROID_STL=gnustl_shared'   //支持C++异常处理标准模板快,ndk16+需要注释
                //abiFilters "armeabi-v7a", "arm64-v8a", "x86_64"
            }
        }
    }
    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 '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'
}

(10)整体目录结构如下，

运行程序，

 

代码链接：

 

 

References:

Https://www.jianshu.com/p/6e16c0429044

https://www.bilibili.com/video/av55834524/

 

 

 

作者：watersink