android JNI学习之一

2022-12-22 19:49:18

执行System.loadLibrary()函数时，VM会反向调用*.so里的JNI_OnLoad()函数。用途有二：
1. VM询问此*.so使用的JNI版本编号。
2. VM要求*.so做一些初期设定工作(Initialization)，例如登记<函数名称表>。

•例如，在Android的jniload.so档案里，就提供了JNI_OnLoad()函数，其程序码片段为：

/* com.misoo.counter.CounterNative.cpp */

#include <stdio.h>

#include<jni.h>

#include <pthread.h>

#include<android/log.h>

#include "com_misoo_counter_CounterNative.h"

//LOGE("ERROR: GetEnv failed\n");

#define LOGE(x)  __android_log_print(ANDROID_LOG_INFO,TAG,(x))

jmethodID mid;

jclass mClass;

JavaVM *jvm;

pthread_t thread;

int n, sum;

const char *TAG="JniTest";

//int  ANDROID_LOG_INFO= 0;

void* trRun(void*);

void JNICALL Java_com_misoo_counter_CounterNative_nativeSetup(JNIEnv *env,

        jobject thiz) {

    jclass clazz = env->GetObjectClass(thiz);

    mClass = (jclass) env->NewGlobalRef(clazz);

    mid = env->GetStaticMethodID(mClass, "callback", "(I)V");

}

void JNICALL Java_com_misoo_counter_CounterNative_nativeExec(JNIEnv *env,

        jobject thiz, jint numb) {

    n = numb;

    pthread_create(&thread, NULL, trRun, NULL);

}

void* trRun(void*) {

    int status;

    JNIEnv *env;

    bool isAttached = false;

    status = jvm->GetEnv((void **) &env, JNI_VERSION_1_4);

    if (status < ) {

        status = jvm->AttachCurrentThread(&env, NULL);

        if (status < )

            return NULL;

        isAttached = true;

    }

    sum = ;

    for (int i = ; i <= n; i++)

        sum += i;

    env->CallStaticVoidMethod(mClass, mid, sum);

    if (isAttached)

        jvm->DetachCurrentThread();

    return NULL;

}

static const char *classPathName = "com/misoo/counter/CounterNative";

static JNINativeMethod methods[] = { { "init", "()V",

        (void *) Java_com_misoo_counter_CounterNative_nativeSetup }, {

        "execute", "(I)V",

        (void *) Java_com_misoo_counter_CounterNative_nativeExec } };

static int registerNativeMethods(JNIEnv* env, const char* className,

        JNINativeMethod* gMethods, int numMethods) {

    __android_log_print(ANDROID_LOG_INFO,TAG,"registerNativeMethods");

    if(env == NULL)

        __android_log_print(ANDROID_LOG_INFO,TAG,"env is null");

    jclass clazz = env->FindClass(className);

    __android_log_print(ANDROID_LOG_INFO,TAG,"find class");

    __android_log_print(ANDROID_LOG_INFO,TAG,"%s",className);

    env->RegisterNatives(clazz, gMethods, numMethods);

    __android_log_print(ANDROID_LOG_INFO,TAG,"end registerNativeMethods");

    return JNI_TRUE;

}

static int registerNatives(JNIEnv* env) {

    __android_log_print(ANDROID_LOG_INFO,TAG,"registerNatives");

    registerNativeMethods(env, classPathName, methods,

            sizeof(methods) / sizeof(methods[]));

    __android_log_print(ANDROID_LOG_INFO,TAG,"end registerNatives");

    return JNI_TRUE;

}

jint JNI_OnLoad(JavaVM* vm, void* reserved) {

    __android_log_print(ANDROID_LOG_INFO,TAG,"JNI_OnLoad");

    JNIEnv *env = NULL;

    jvm = vm;

     if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {

            LOGE("ERROR: GetEnv failed\n");

//            return -1;

        }

//    assert(env == NULL);

    if (registerNatives(env) != JNI_TRUE)

        return -;

    __android_log_print(ANDROID_LOG_INFO,TAG,"JNI_OnLoad end");

    return JNI_VERSION_1_4;

}

Android.mk文件是：

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_LDLIBS:=-L$(SYSROOT)/usr/lib -llog

LOCAL_MODULE    :=jniload

LOCAL_SRC_FILES :=archMultiThread.cpp

include $(BUILD_SHARED_LIBRARY)

Application.mk文件：

APP_STL:=gnustl_static

APP_CPPFLAGS:=-frtti -fexceptions

APP_ABI:=armeabi armeabi-v7a

APP_PLATFORM=android-8

CounterNative.java

package com.misoo.counter;

import com.example.hellondk.MainActivity;

import android.os.Handler;

import android.os.Message;

import android.util.Log;

//CounterNative.java

// ………

public class CounterNative {

    private static Handler h;

    public static final String TAG = "JniTest";

    static {

        Log.i(CounterNative.TAG, "try to load libMyJT002.so");

        System.loadLibrary("jniload");

        Log.i(CounterNative.TAG, "end try to load libMyJT002.so");

    }

    public CounterNative() {

        Log.i(CounterNative.TAG, "new CounterNative");

        init();

        Log.i(CounterNative.TAG, "init finished");

        h = new Handler() {

            public void handleMessage(Message msg) {

                MainActivity.ref.setTitle("Hello …");

            }

        };

    }

    private static void callback(int a) {

        Message m = h.obtainMessage(1, a, 3, null);

        h.sendMessage(m);

    }

    private native void init();

    public native void execute(int numb);

}

package com.example.hellondk;

import java.sql.Ref;

import com.huml.ndk1.NativeJniAdder;

import com.misoo.counter.CounterNative;

import android.app.Activity;

import android.os.Bundle;

import android.util.Log;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

public class MainActivity extends Activity {

    public static MainActivity ref = null;

    CounterNative obj;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        ref= this;

        Log.i(CounterNative.TAG, "onCreate");

        obj = new CounterNative();

    }

//对应一个Button的onClick事件，布局文件中一个Button按钮，布局文件很简单我就不列出来了

    public void TestNDK(View view){

        Log.i(NativeJniAdder.TAG, "start NDK");

        obj.execute(11);

    }

}

码农公寓

相关文章