ndk开发中,在c中调用java代码

在ndk开发中,在c中调用java代码其实是通过反射技术来实现的。

代码的下载链接为:http://download.csdn.net/detail/caihongshijie6/6649995

1、main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <TextView        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/hello_world" />    <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="c代码呼叫java的空方法"        android:onClick="click1"         />    <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="c代码呼叫java的两个int参数的方法"        android:onClick="click2"         />        <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="c代码呼叫java的string参数方法"        android:onClick="click3"         />                <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="c代码呼叫java的静态string参数方法"        android:onClick="click4"         />                                <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="在mainactivity里面调用空方法"        android:onClick="click5"         /></LinearLayout>

2、DataProvider

package com.njupt.ndk_callback;public class DataProvider {//C调用java空方法public void helloFromJava(){System.out.println("hello from java");}//C调用java中的带两个int参数的方法public int Add(int x,int y){int result = x+y;System.out.println("java result: " + result);return result;}//C调用java中参数为string的方法public void printString(String s){System.out.println("java " + s);}public static void printStaticStr(String s){System.out.println("java static " + s);}//让c代码调用对应的java代码public native void callmethod1();public native void callmethod2();public native void callmethod3();//调用一个静态的c代码public native void callmethod4();}

3、MainActivity

package com.njupt.ndk_callback;import android.os.Bundle;import android.app.Activity;import android.view.Menu;import android.view.View;public class MainActivity extends Activity {static{System.loadLibrary("Hello");}private DataProvider dp;//用语言是native方法和所调用的java代码不在同一个类中...它所调用的是DataProvider中的一个printString()方法..public native void call_dp_method1();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);dp = new DataProvider();}public void click1(View v){dp.callmethod1();}public void click2(View v){dp.callmethod2();}public void click3(View v){dp.callmethod3();}public void click4(View v){dp.callmethod4();}public void click5(View v){call_dp_method1();}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

4、Hello.c

#include <stdio.h>#include <jni.h>#include "com_njupt_ndk_callback_DataProvider.h"#include "com_njupt_ndk_callback_MainActivity.h"#include <android/log.h>//include  D:\android-ndk-r7b\platforms\android-8\arch-arm\usr\include\android下的log.h这个目录#define LOG_TAG "System.out"#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)JNIEXPORT void JNICALL Java_com_njupt_ndk_1callback_DataProvider_callmethod1  (JNIEnv * env, jobject obj){//在c代码里面调用java代码里面的方法// java 反射    //1 . 找到java代码的 class文件//    jclass      (*FindClass)(JNIEnv*, const char*);jclass dpclazz = (*env)->FindClass(env,"com/njupt/ndk_callback/DataProvider");if(dpclazz == 0){LOGI("find class error");return ;}LOGI("find class ...");//2 寻找class里面的方法//   jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*)jmethodID method1 = (*env)->GetMethodID(env,dpclazz,"helloFromJava","()V");if(method1 == 0){LOGI("find method1 error..");return ;}LOGI("find method1 ...");//3 .调用这个方法//    void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);(*env)->CallVoidMethod(env,obj,method1);}JNIEXPORT void JNICALL Java_com_njupt_ndk_1callback_DataProvider_callmethod2  (JNIEnv * env , jobject obj){jclass dpclazz = (*env)->FindClass(env,"com/njupt/ndk_callback/DataProvider");if(dpclazz == 0){LOGI("find class error");return ;}LOGI("find class ...");jmethodID method2 = (*env)->GetMethodID(env,dpclazz,"Add","(II)I");if(method2 == 0){LOGI("find method2 error..");return ;}LOGI("find method2 ...");// 3 调用这个方法//    jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);int result = (*env)->CallIntMethod(env,obj,method2,3,5);LOGI("c code Result = %d", result);}JNIEXPORT void JNICALL Java_com_njupt_ndk_1callback_DataProvider_callmethod3  (JNIEnv * env, jobject obj){jclass dpclazz = (*env)->FindClass(env,"com/njupt/ndk_callback/DataProvider");if(dpclazz == 0){LOGI("find class error");return ;}LOGI("find class ...");jmethodID method3 = (*env)->GetMethodID(env,dpclazz,"printString","(Ljava/lang/String;)V");if(method3 == 0){LOGI("find method3 error..");return ;}LOGI("find method3 ...");(*env)->CallVoidMethod(env,obj,method3,(*env)->NewStringUTF(env,"hello in c"));}JNIEXPORT void JNICALL Java_com_njupt_ndk_1callback_DataProvider_callmethod4  (JNIEnv * env, jobject obj){jclass dpclazz = (*env)->FindClass(env,"com/njupt/ndk_callback/DataProvider");if(dpclazz == 0){LOGI("find class error");return ;}LOGI("find class ...");//2 寻找class里面的方法//   jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);// 注意 :如果要寻找的方法是静态的方法 那就不能直接去获取methodid//jmethodID method4 = (*env)->GetMethodID(env,dpclazz,"printStaticStr","(Ljava/lang/String;)V");//    jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);jmethodID method4 = (*env)->GetStaticMethodID(env,dpclazz,"printStaticStr","(Ljava/lang/String;)V");if(method4 == 0){LOGI("find method4 error..");return ;}LOGI("find method4 ...");//3.调用一个静态的java方法//    void        (*CallStaticVoidMethod)(JNIEnv*, jclass, jmethodID, ...);(*env)->CallStaticVoidMethod(env,dpclazz,method4,(*env)->NewStringUTF(env,"static haha in c"));}JNIEXPORT void JNICALL Java_com_njupt_ndk_1callback_MainActivity_call_1dp_1method1(JNIEnv * env, jobject obj) {jclass dpclazz = (*env)->FindClass(env,"com/njupt/ndk_callback/DataProvider");if(dpclazz == 0) {LOGI("find class error");return;}LOGI("find class ...");jmethodID method5 = (*env)->GetStaticMethodID(env,dpclazz,"printString","(Ljava/lang/String;)V");if(method5 == 0) {LOGI("find method5 error..");return;}LOGI("find method5 ...");//3 .调用这个方法(用于解决native方法和所调用的java代码不在同一个类中的情况..)//    void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);//    jobject     (*NewObject)(JNIEnv*, jclass, jmethodID, ...);//  jobject     (*AllocObject)(JNIEnv*, jclass);jobject dpobject = (*env)->AllocObject(env,dpclazz);(*env)->CallStaticVoidMethod(env,dpobject,method5,(*env)->NewStringUTF(env,"not int a class ,static hello jni"));}

5、Android.mk

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

------------------------------------------------------以下介绍在这个过程中需要用到的命令-------------------------------

1、javah命令

用于生成.h文件。

使用场景：cmd下进入到src目录后 javah  包名+类名

2、javap命令

用于生成某一个类中的所有方法的方法签名

使用场景：cmd下进入到bin/classes目录后javap  包名+类名

3、ndk-build命令

用于生成.so文件

使用场景：在cygwin下进入到工程目录后,直接输入ndk-build