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NDK开发①开发流程

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Java编写native方法

新建JniUtil类如下:

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public class JniUtil {
	
	/**
	 * 回调接口
	 * @author jimi098
	 *
	 */
	public interface IRecFrameListener {
		
		public void onRecFrameListener(String result);
	}
	
	private IRecFrameListener mListener;
	
	
	static {
		
		System.loadLibrary("test");
	}
	
	
	public void setOnRecFrameListener(IRecFrameListener listener) {
		
		mListener = listener;
	}
	
	/**
	 * 供jni调用的java方法
	 * @param result
	 */
	public void onRecFrame(int result) {
		mListener.onRecFrameListener(String.valueOf(result));
	}
	
	//java本地方法
	public native int init();
	public native int add(int a,int b);
	public native String getString(String input);
}

生成.h头文件

编译JniUtil类，生成JniUtil.class文件，然后在cmd中切换目录至android工程的src文件夹路径，运行javah -jni com.example.demo.JniUtil命令即可生成.h头文件

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#include <jni.h>
#include <android/log.h>
//logcat日志
#define  LOG_TAG    "Test"
#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
/* Header for class com_example_demo_JniUtil */
#ifndef _Included_com_example_demo_JniUtil
#define _Included_com_example_demo_JniUtil
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_demo_JniUtil
 * Method:    init
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_com_example_demo_JniUtil_init
  (JNIEnv *, jobject);
/*
 * Class:     com_example_demo_JniUtil
 * Method:    add
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_example_demo_JniUtil_add
  (JNIEnv *, jobject, jint, jint);
/*
 * Class:     com_example_demo_JniUtil
 * Method:    getString
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_demo_JniUtil_getString
  (JNIEnv *, jobject, jstring);
#ifdef __cplusplus
}
#endif
#endif

实现jni

新建jni文件夹，实现本地java方法

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#include<jniutil.h>
jobject mObject;
JNIEXPORT jint JNICALL Java_com_example_demo_JniUtil_init(JNIEnv *env,
		jobject obj) {
	//获取全局对象
	mObject = (*env)->NewGlobalRef(env, obj);
	jmethodID methodID;
	jclass mClass;
	//查找指定名称类
	mClass = (*env)->GetObjectClass(env, mObject);;
	//获取方法ID
	methodID = (*env)->GetMethodID(env,mClass,"onRecFrame","(I)V");
	//调用上层java方法
	(*env)->CallVoidMethod(env,obj,methodID,89);
	return 5;
}
/*
 * Class:     com_example_demo_JniUtil
 * Method:    add
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_example_demo_JniUtil_add(JNIEnv *env,
		jobject obj, jint x, jint y) {
	return x + y;
}
/*
 * Class:     com_example_demo_JniUtil
 * Method:    getString
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_example_demo_JniUtil_getString(JNIEnv *env,
		jobject obj, jstring result) {
	return result;
}

编写mk文件

Android.mk

指定编译规则

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LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    := test
LOCAL_SRC_FILES := test.c
LOCAL_LDLIBS    := -llog
include $(BUILD_SHARED_LIBRARY)

Application.mk

指定编译平台

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APP_ABI := armeabi armeabi-v7a
APP_PLATFORM := android-22
APP_STL:=gnustl_static
APP_CPPFLAGS:=-frtti -fexceptions

配置NDK执行编译

右击工程–》Properties–》Builders–》New–》选择Program–》Main–》Location：选择ndk-build.cmd命令路径–》Working Directory：选择工程路径–》Refresh–》Build Options，配置完成后即可自动编译，不需要安装cygwin linux模拟环境

应用jni

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public class MainActivity extends Activity implements OnClickListener, IRecFrameListener {
	
	private Button mButton;
	
	private JniUtil mJniUtil;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        mButton = (Button) findViewById(R.id.btn_click);
        mButton.setOnClickListener(this);
        mJniUtil = new JniUtil();
        mJniUtil.setOnRecFrameListener(this);
        
    }
	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		System.out.println("init: " + mJniUtil.init());
		System.out.println("sum: "+ mJniUtil.add(1, 2));
		System.out.println("getString: " + mJniUtil.getString("wert"));
	}
	/**
	 * 回调，由jni方法返回数据
	 */
	@Override
	public void onRecFrameListener(String result) {
		// TODO Auto-generated method stub
		System.out.println(result);
		
	}
}

Android Studio 2.2 开发NDK

NDK开发基础①使用Android Studio编写NDK

Gradle配置NDK

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android {
    compileSdkVersion 25
    buildToolsVersion "25.0.1"
    defaultConfig {
        applicationId "com.michael.lplayer"
        minSdkVersion 15
        targetSdkVersion 22
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ""
                arguments '-DANDROID_TOOLCHAIN=clang'
                abiFilters "armeabi-v7a"
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    //加载外部so库
    sourceSets.main {
        jniLibs.srcDirs = ['libs']
        jni.srcDirs = []
    }
}

CMakeLists.txt 配置

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# Sets the minimum version of CMake required to build the native
# library. You should either keep the default value or only pass a
# value of 3.4.0 or lower.
cmake_minimum_required(VERSION 3.4.1)
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 )
set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)
include_directories(libs/include)
add_library( avutil-55
             SHARED
             IMPORTED )
set_target_properties( avutil-55
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libavutil-55.so )
add_library( swresample-2
             SHARED
             IMPORTED )
set_target_properties( swresample-2
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libswresample-2.so )
add_library( avcodec-57
             SHARED
             IMPORTED )
set_target_properties( avcodec-57
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libavcodec-57.so )
add_library( avfilter-6
             SHARED
             IMPORTED)
set_target_properties( avfilter-6
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libavfilter-6.so )
add_library( swscale-4
             SHARED
             IMPORTED)
set_target_properties( swscale-4
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libswscale-4.so )
add_library( avformat-57
             SHARED
             IMPORTED)
set_target_properties( avformat-57
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libavformat-57.so )
#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
add_library( ffmpeg
             SHARED
             src/main/cpp/ffmpeg_decode.c )
#target_include_directories(ffmpeg PRIVATE libs/include)
target_link_libraries( ffmpeg avutil-55 swresample-2  avcodec-57 avfilter-6 swscale-4 avformat-57
                       ${log-lib} )
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