JNI method

 

package com.example.register;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {
    private static final String TAG = "HTC+++";

    public int age;

    static {
        System.loadLibrary("hello-jni");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initData();
        setContentView(R.layout.activity_main);

        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(this);
    }

    private void initData() {
        age = 10;
    }

    private void calledByNative() {
        Log.d(TAG, "java layer: called By Native");
    }

    private static void staticMethod(int value) {
        Log.d(TAG, "java layer: static method called By Native. value: "
                + value);
    }

    private int multi(int a, int b) {
        return a * b;
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.button:
                print("I want to print");
                int result = add(123, 456);
                Log.d(TAG, "123 + 456 = " + result);
                String s = getString();
                Log.d(TAG, "getString() = " + s);
                callJava();
                changeintField(111);
                Log.d(TAG, "age:" + age);
                break;
            default:
                break;
        }

    }

    private native void print(String str);

    private native int add(int a, int b);

    private native String getString();

    private native void callJava();

    private native void changeintField(int value);
}

 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xxxx" />

</LinearLayout>

 

// jni/Android.mk
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := hello-jni
LOCAL_SRC_FILES := dynamic_jni.c \
      static_jni.c
LOCAL_LDLIBS :=-llog

include $(BUILD_SHARED_LIBRARY)

 

// jni/Application.mk
APP_ABI := all

 

// jni/dynamic_jni.c
#include <string.h>
#include <jni.h>
#include <android/log.h>

#define LOG_TAG "HTC+++"

#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,LOG_TAG,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,LOG_TAG,__VA_ARGS__)


void callJavaMethod(JNIEnv *env, jobject thiz) {
    jclass cls = (*env)->GetObjectClass(env, thiz);
    jmethodID methodId = (*env)->GetMethodID(env, cls, "calledByNative", "()V");
    (*env)->CallVoidMethod(env, thiz, methodId);

    jmethodID staticMethod = (*env)->GetStaticMethodID(env, cls, "staticMethod", "(I)V");
    (*env)->CallStaticVoidMethod(env, cls, staticMethod, 999);

    jmethodID multiMethod = (*env)->GetMethodID(env, cls, "multi", "(II)I");
    jint result = (*env)->CallIntMethod(env, thiz, multiMethod, 100, 200);
    LOGD("multi: 100 * 200 = %d", result);
}

void changeIntField(JNIEnv *env, jobject thiz, jint newValue) {
    jclass cls = (*env)->GetObjectClass(env, thiz);
    jfieldID fieldId = (*env)->GetFieldID(env, cls, "age", "I");
    jint age = (*env)->GetIntField(env, thiz, fieldId);
    LOGD("Native: current age:%d", age);
    (*env)->SetIntField(env, thiz, fieldId, newValue);
}


void nativePrint(JNIEnv *env, jobject thiz, jstring jstr) {
    const char *nativeString = (*env)->GetStringUTFChars(env, jstr, 0);
    LOGD("nativePrint() String:%s", nativeString);

    //java中有垃圾回收机制，而c语言没有，那么使用完该字符串之后该如何处理呢？
    //字符串str使用完后，需要通知虚拟机平台相关代码无需再访问
    //如果是中文则需要转码
    (*env)->ReleaseStringUTFChars(env, jstr, nativeString);
}

jint nativeAdd(JNIEnv *env, jobject thiz, jint a, jint b) {
    return a + b;
}
/*
jstring newString(JNIEnv *env, jobject thiz) {
    return (*env)->NewStringUTF(env, "Hello from JNI !");
}
*/

static JNINativeMethod gMethods[] = {
        {"print",          "(Ljava/lang/String;)V",       (void*) nativePrint },
        {"add",            "(II)I",                       (void*) nativeAdd },
  //      {"getString",      "()Ljava/lang/String;",        (void*) newString },
        {"callJava",       "()V",                         (void*) callJavaMethod },
        {"changeintField",   "(I)V",                        (void*) changeIntField }
};

static int registerMethods(JNIEnv * env) {
    jclass clazz = (*env)->FindClass(env, "com/example/register/MainActivity");
    int size = sizeof(gMethods) / sizeof(gMethods[0]);
    if ((*env)->RegisterNatives(env, clazz, gMethods, (jint) size) != JNI_OK) {
        return -1;
    }


    return 0;
}

jint JNI_OnLoad(JavaVM *vm, void *reserved) {
    JNIEnv* env = NULL;
    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        return -1;
    }

    if (registerMethods(env) != 0) {
        return -1;
    }

    return JNI_VERSION_1_4;
}

 

// static_jni.c
#include <string.h>
#include <jni.h>
#include <android/log.h>

#define LOG_TAG "MainActivity"

#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,LOG_TAG,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,LOG_TAG,__VA_ARGS__)

jstring Java_com_example_register_MainActivity_getString(JNIEnv* env,
        jobject thiz) {

    return (*env)->NewStringUTF(env, "Hello from static JNI !");
}