Android-NDK开发之第四个例子--用C/C 调用Java

  用C/C++调用Java的方法我没有去研究，也不知道从哪里开始研究，对Linux我了解到很少，希望有朋友可以给些资料，我的水平很差，望大家多多包涵。

  这个例子是别人的代码，我忘记从来里弄来的了，先对原作者表示抱歉。同时代码也被我修改过，再次道歉。

  而此文和别的文章一样，只是作为我平时学习积累的验证。

  1. Android.mk文件：

LOCAL_SRC_FILES参数用空格隔开

LOCAL_PATH:=$(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE:=native
LOCAL_SRC_FILES:=geolo.cpp my_jni.h
include $(BUILD_SHARED_LIBRARY)

 

2. geolo.cpp

先用FindClass方法找到java类，有点类似java的反射用LoadClass

再用CallObjectMethod方法调用Java类的函数。

#include "my_jni.h"
jobject getInstance(JNIEnv* env, jclass obj_class){
    jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");
    jobject obj = env->NewObject(obj_class, construction_id);
    return obj;
}
JNIEXPORT jstring JNICALL Java_com_easepal_geolo_CActivityMain_stringFromJNI(JNIEnv* env, jobject thiz){
   jstring str;
   jclass java_class = env->FindClass("com/easepal/geolo/CForCall");
    if (java_class == 0){
       return env->NewStringUTF("not find class!");
    }
   jobject java_obj = getInstance(env, java_class);
   if (java_obj == 0){
       return env->NewStringUTF("not find java OBJ!");
   }
   jmethodID java_method = env->GetMethodID(java_class, "GetJavaString", "()Ljava/lang/String;");
   if(java_method == 0){
       return env->NewStringUTF("not find java method!");
   }
   str = (jstring)env->CallObjectMethod(java_obj, java_method);
   return str;
}

 

3. my_jni.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_easepal_geolo_CActivityMain */
#ifndef _Included_com_easepal_geolo_CActivityMain
#define _Included_com_easepal_geolo_CActivityMain
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:     com_easepal_geolo_CActivityMain
* Method:    stringFromJNI
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_easepal_geolo_CActivityMain_stringFromJNI(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif

 

4. CActivityMain.java

package com.easepal.geolo;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class CActivityMain extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(this);
        tv.setText( stringFromJNI("hello") );
        setContentView(tv);
    }


    static {
        System.loadLibrary("native");
    }
    public native String stringFromJNI(String str);
}

 

5. CForCall.java

package com.easepal.geolo;
public class CForCall{
   public CForCall(){};
   //public ~CForCall(){};
   public String GetJavaString(){
       String str;
       str = "123456";
       return str;