android NDK 四、 Java call Native And Native call Java

1、在java中调用 Native代码，JNI的写法

#include <string.h>
#include <jni.h>
#include <stdio.h>
#include <android/log.h>

#define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "native-activity", __VA_ARGS__))

JNIEXPORT jstring JNICALL
Java_com_ndk_NDKFirstActivity_getTime( JNIEnv* env,jobject thiz )
{
    LOGI("hello lipeil ,you are great ! hh");
    return (*env)->NewStringUTF(env, "the time is 2012 5 17");
}

JNIEXPORT jstring JNICALL
Java_com_ndk_NDKFirstActivity_getLine(JNIEnv* env , jobject thiz , jstring jstr)
{
    char buf[128];
    const jbyte *str;
    str = (*env)->GetStringUTFChars(env ,jstr, NULL);
    if(str == NULL)
    {
        return NULL;
    }
    
    LOGI(str);
    (*env)->ReleaseStringUTFChars(env,jstr,str);
    
    return (*env)->NewStringUTF(env,"yo ni yao diao");
}
/**整型数组的转换*/
JNIEXPORT jint JNICALL
Java_com_ndk_NDKFirstActivity_sumArrayRegion(JNIEnv* env , jobject thiz , jintArray arr)
{
    jint buf[10];
    jint i, sum=0;
    (*env)->GetIntArrayRegion(env , arr ,0,10,buf);
    for(i=0 ; i<10 ;i++)
    {
        sum += buf[i];
    }
    return sum;
    
}

JNIEXPORT jint JNICALL
Java_com_ndk_NDKFirstActivity_sumArray(JNIEnv* env , jobject thiz , jintArray arr)
{
    
    jint i=0, sum=0;// 需要先初始化
    jint* buf ;
    buf= (*env)->GetIntArrayElements(env , arr ,NULL);
    if(buf == NULL)
    {
        return 0;
    }
    /**
    or we can use GetArrayLength get the buf length;
    */
    while(*(buf+i) !='\0')
    {
        sum += buf[i];
        i++;
    }
    (*env)->ReleaseIntArrayElements(env ,arr ,buf ,0);
    return sum;
    
}

2、 在Native 中回调 Java代码，写法

#include <string.h>
#include <jni.h>
#include <stdio.h>
#include <android/log.h>

#define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "native-activity", __VA_ARGS__))
#define LOGII(...) ((void)__android_log_print(ANDROID_LOG_INFO, "the int value is : %d", __VA_ARGS__))

JNIEXPORT void JNICALL
Java_com_ndk_NDKFirstActivity_acessField(JNIEnv * env , jobject obj)
{
    jfieldID fid;
    jstring jstr;
    const char* str;
    
    /**从对象中回去类*/
    jclass cls = (*env)->GetObjectClass(env ,obj);
    /**根据类、字段、和字段类型获取字段id*/
    fid = (*env)->GetFieldID(env ,cls,"str" ,"Ljava/lang/String;");//类型后面的分号不能省略
    
    if(fid == NULL)
    {
        return;
    }
    
    /**根据字段ID 和对象 获取值*/
    jstr = (*env)->GetObjectField(env ,obj,fid);
    str = (*env)->GetStringUTFChars(env ,jstr ,NULL);
    if(str == NULL)
    {
        return;
    }
    LOGI(str);
    (*env)->ReleaseStringUTFChars(env ,jstr,str);
    
    jstr = (*env)->NewStringUTF(env ,"I reset the str value in native c,and success");
    if(jstr == NULL)
    {
        return;
    }
    
    /**根据对象、字段id 设置值*/
    (*env)->SetObjectField(env ,obj , fid , jstr);
}

JNIEXPORT void JNICALL
Java_com_ndk_NDKFirstActivity_accessStaticField(JNIEnv *env ,jobject obj)
{
    jfieldID fid ;
    jint si;
    jclass cls = (*env)->GetObjectClass(env , obj);
    
    fid = (*env)->GetStaticFieldID(env ,cls ,"value","I");
    if(fid==NULL)
    {
        return;
    }
//根据类，设置静态字段值
    si = (*env)->GetStaticIntField(env ,cls ,fid);
    //LOGI(si+"");
    (*env)->SetStaticIntField(env ,cls ,fid ,2012);
}

JNIEXPORT void JNICALL
Java_com_ndk_NDKFirstActivity_invokeMethod(JNIEnv *env ,jobject obj)
{
    jclass cls = (*env)->GetObjectClass(env ,obj);
    jmethodID mid = (*env)->GetMethodID(env ,cls ,"callback","()V");
    
    if(mid == NULL)
    {
        return;
    }
    //更加对象、方法字段，调用 Java 方法
    LOGI("i invoke callback in native c");
    (*env)->CallVoidMethod(env ,obj ,mid);
}

JNIEXPORT void JNICALL
Java_com_ndk_NDKFirstActivity_invokeStaticMethod(JNIEnv *env , jobject obj)
{
    jclass cls = (*env)->GetObjectClass(env , obj);
    
    jmethodID mid =(*env)->GetStaticMethodID(env ,cls,"staticCallback","(I)V");
    if(mid == NULL)
    {
        return;
    }
    LOGI("i invoke staticCallback in native c");
    jint ji = 1000;
//根据类，方法字段，调用静态方法
    (*env)->CallStaticVoidMethod(env,cls,mid ,ji);
}

JNIEXPORT jobject JNICALL
Java_com_ndk_NDKFirstActivity_getData(JNIEnv *env , jobject obj , jint ji)
{
//根据类名，获取类
    jclass dataClass = (*env)->FindClass(env ,"com/ndk/Data");
    if(dataClass == NULL)
    {
        return;
    }
    //根据类 获取方法字段
    jmethodID cid = (*env)->GetMethodID(env ,dataClass ,"<init>" ,"(I)V");
    
    if(cid== NULL)
    {
        return;
    }
    LOGI("i init and return a construct in native c");
//根据类、 构造方法字段 初始化 类对象
    return (*env)->NewObject(env ,dataClass ,cid , ji);
}