JNI java调用c代码 (一）静态注册

今天说的代码是从java层调用c代码，然后再反调java代码的。这里在java用的是静态注册，也就是jni方法名是根据java的文件路径生成的，不是动态注册。

一、java调用jni，静态注册

先看：java注册jni，以及调用jni函数：

package com.duicky;import android.app.Activity;import android.content.Context;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;/** * C 调用 Java 例子 *  * @author luxiaofeng * */public class MainActivity extends Activity {//也就是你mk配置文件中的  LOCAL_MODULE    := NDK_03private static final String libSoName = "NDK_04";private static final String tag = "MainActivity";public static Context mContext = null;private Button btnClickStatic = null;private Button btnClick = null;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                mContext = this;        //初始化控件        initViews();    }        /**     * 初始化控件     */    private void initViews() {        btnClick = (Button) this.findViewById(R.id.btn_click);        btnClick.setOnClickListener(new OnClickListener() {public void onClick(View v) {sayHello();}});                        btnClickStatic = (Button) this.findViewById(R.id.btn_click_static);        btnClickStatic.setOnClickListener(new OnClickListener() {public void onClick(View v) {getTime();}});}    public native void getTime() ;        public native void sayHello() ;        /**     * 载入JNI生成的so库文件     */    static {        System.loadLibrary(libSoName);    }    }

二、JNI的Android.mk

然后我们再看JNI的mk函数：

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_C_INCLUDES := $(LOCAL_PATH)/includeLOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -llogLOCAL_MODULE    := NDK_04LOCAL_SRC_FILES := \CToJava.c \Provider.cinclude $(BUILD_SHARED_LIBRARY)

是动态库，需要在libs加载libNDK_04.so动态库

三、jni函数

jni函数，当java传下来，就带有了JNIEnv参量

#include <string.h>#include <android/log.h>#include <jni.h>#include "Provider.h"JNIEnv* jniEnv;/** *  Java 中 声明的native getTime 方法的实现 */void Java_com_duicky_MainActivity_getTime(JNIEnv* env, jobject thiz){if(jniEnv == NULL) {jniEnv = env;}GetTime();}/** *  Java 中 声明的native sayHello 方法的实现 */void Java_com_duicky_MainActivity_sayHello(JNIEnv* env, jobject thiz){if (jniEnv == NULL) {jniEnv = env;}SayHello();}

下面这个类是c中的方法，以及获取java类，和方法的初始化

#include "Provider.h"#include <android/log.h>extern JNIEnv* jniEnv;jclass TestProvider;jobject mTestProvider;jmethodID getTime;jmethodID sayHello;int GetProviderInstance(jclass obj_class);/** * 初始化 类、对象、方法 */int InitProvider() {__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  1" );if(jniEnv == NULL) {return 0;}if(TestProvider == NULL) {TestProvider = (*jniEnv)->FindClass(jniEnv,"com/duicky/TestProvider");if(TestProvider == NULL){return -1;}__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  2 ok" );}if (mTestProvider == NULL) {if (GetProviderInstance(TestProvider) != 1) {(*jniEnv)->DeleteLocalRef(jniEnv, TestProvider);return -1;}__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  3 ok" );}if (getTime == NULL) {getTime = (*jniEnv)->GetStaticMethodID(jniEnv, TestProvider, "getTime","()Ljava/lang/String;");if (getTime == NULL) {(*jniEnv)->DeleteLocalRef(jniEnv, TestProvider);(*jniEnv)->DeleteLocalRef(jniEnv, mTestProvider);return -2;}__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  4 ok" );}if (sayHello == NULL) {sayHello = (*jniEnv)->GetMethodID(jniEnv, TestProvider, "sayHello","(Ljava/lang/String;)V");if (sayHello == NULL) {(*jniEnv)->DeleteLocalRef(jniEnv, TestProvider);(*jniEnv)->DeleteLocalRef(jniEnv, mTestProvider);(*jniEnv)->DeleteLocalRef(jniEnv, getTime);return -3;}__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  5 ok" );}__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitProvider Begin  6" );return 1;}int GetProviderInstance(jclass obj_class) {if(obj_class == NULL) {return 0;}jmethodID construction_id = (*jniEnv)->GetMethodID(jniEnv, obj_class,"<init>", "()V");if (construction_id == 0) {return -1;}mTestProvider = (*jniEnv)->NewObject(jniEnv, obj_class,construction_id);if (mTestProvider == NULL) {return -2;}return 1;}/** * 获取时间 ---- 调用 Java 方法 */void GetTime() {if(TestProvider == NULL || getTime == NULL) {int result = InitProvider();if (result != 1) {return;}}jstring jstr = NULL;char* cstr = NULL;__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime Begin" );jstr = (*jniEnv)->CallStaticObjectMethod(jniEnv, TestProvider, getTime);cstr = (char*) (*jniEnv)->GetStringUTFChars(jniEnv,jstr, 0);__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "Success Get Time from Java , Value = %s",cstr );__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime End" );(*jniEnv)->ReleaseStringUTFChars(jniEnv, jstr, cstr);(*jniEnv)->DeleteLocalRef(jniEnv, jstr);}/** * SayHello ---- 调用 Java 方法 */void SayHello() {if(TestProvider == NULL || mTestProvider == NULL || sayHello == NULL) {int result = InitProvider() ;if(result != 1) {return;}}jstring jstrMSG = NULL;jstrMSG =(*jniEnv)->NewStringUTF(jniEnv, "Hi,I'm From C");__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello Begin" );(*jniEnv)->CallVoidMethod(jniEnv, mTestProvider, sayHello,jstrMSG);__android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello End" );(*jniEnv)->DeleteLocalRef(jniEnv, jstrMSG);}

四、java函数

最后再反调用java的方法

package com.duicky;public class TestProvider {public static String getTime() {LogUtils.printWithSystemOut( "Call From C Java Static Method"   );LogUtils.toastMessage(MainActivity.mContext, "Call From C Java Static Method"   );return String.valueOf(System.currentTimeMillis());}public void sayHello(String msg) {LogUtils.printWithSystemOut("Call From C Java Not Static Method ：" + msg);LogUtils.toastMessage(MainActivity.mContext, "Call From C Java Not Static Method ：" + msg);}}