jni使用基础（九）之c调用java事例demo

最新推荐文章于 2021-02-15 22:24:45 发布

hudan2714

最新推荐文章于 2021-02-15 22:24:45 发布

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分类专栏： java c Android 文章标签： java jni c android layout class

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本文介绍了一个Java应用程序如何通过JNI调用C语言编写的函数的具体实现过程。包括创建Java类、定义本地方法、编写对应的C语言源文件、构建Makefile及配置Android XML布局等内容。

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1.Activity

package com.devchina.ndk4;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;

public class DevchinaActivity extends Activity {
    
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    
    public void click(View view){
    	DevchinaProvider devchina = new DevchinaProvider();
    	devchina.cCallJava();
    }
    
    
    public void clickAdd(View view){
    	DevchinaProvider devchina = new DevchinaProvider();
    	devchina.cCallAdd();
    }
    
    public void clickStrng(View view){
    	DevchinaProvider devchina = new DevchinaProvider();
    	devchina.cCallString();
    }
    
}

2.native

package com.devchina.ndk4;

public class DevchinaProvider {
	static  {
		System.loadLibrary("devchina");
	}
	
	public native void cCallJava(); 
	public native void cCallString();
	public native int  cCallAdd();
	
	
	//1.调用java空方法
	public void callJava(){
		System.out.println("i come from java");
	}

	public int add(int x,int y){
		System.out.println("devchina java res = "+(x+y));
		return x+y;
	}
	
	public void printString(String s){
		System.out.println("devchina java "+ s);
	}
}

3.h文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_devchina_ndk4_DevchinaProvider */

#ifndef _Included_com_devchina_ndk4_DevchinaProvider
#define _Included_com_devchina_ndk4_DevchinaProvider
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_devchina_ndk4_DevchinaProvider
 * Method:    cCallJava
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_devchina_ndk4_DevchinaProvider_cCallJava
  (JNIEnv *, jobject);

/*
 * Class:     com_devchina_ndk4_DevchinaProvider
 * Method:    cCallAdd
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_com_devchina_ndk4_DevchinaProvider_cCallAdd
  (JNIEnv *, jobject);

/*
 * Class:     com_devchina_ndk4_DevchinaProvider
 * Method:    cCallString
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_devchina_ndk4_DevchinaProvider_cCallString
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

4.c文件

#include<stdio.h>
#include<jni.h>
#include"com_devchina_ndk4_DevchinaProvider.h"
#include <android/log.h>
#define LOG_TAG "devchina"
#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_devchina_ndk4_DevchinaProvider_cCallJava
  (JNIEnv * env, jobject obj){//ojb,谁调用了此Native方法，这个Obj就是谁
	//new 出java对象
	jclass clazz = (*env)->FindClass(env,"com/devchina/ndk4/DevchinaProvider");//注意：不能为“.”
	if(clazz==0){//没有找到类
		LOGI("can't find devchina class");
	}else{
		LOGI("find dechina class");
	}

	//获取类中的方法
	jmethodID j_method = (*env)->GetMethodID(env,clazz,"callJava","()V");//最后一个参数是表示方法的签名
	if(j_method==0){
		LOGI("can't get method");
	}else{
		LOGI("get method");
	}

	(*env)->CallVoidMethod(env,obj,j_method);//第二个参数表示调用的类对象
}

JNIEXPORT jint JNICALL Java_com_devchina_ndk4_DevchinaProvider_cCallAdd
  (JNIEnv * env, jobject obj){
	//1.new java obj
	jclass clazz = (*env)->FindClass(env,"com/devchina/ndk4/DevchinaProvider");
    //2.get method id
	jmethodID mId = (*env)->GetMethodID(env,clazz,"add","(II)I");
	//3.invoke method
	jint res = (*env)->CallIntMethod(env,obj,mId,5,6);
	LOGI("c log %d",res);

}


JNIEXPORT void JNICALL Java_com_devchina_ndk4_DevchinaProvider_cCallString
  (JNIEnv * env, jobject obj){
	jclass clazz = (*env)->FindClass(env,"com/devchina/ndk4/DevchinaProvider");
	jmethodID mId = (*env)->GetMethodID(env,clazz,"printString","(Ljava/lang/String;)V");
	(*env)->CallVoidMethod(env,obj,mId,(*env)->NewStringUTF(env," devchina from c "));
}

5.mk文件

LOCAL_PATH := $(call my-dir)
 
include $(CLEAR_VARS) 
 
LOCAL_MODULE    :=devchina
LOCAL_SRC_FILES :=devchina.c

LOCAL_LDLIBS += -llog
 
include $(BUILD_SHARED_LIBRARY)

6.xml文件

<?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" >

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="调用c代码"
        android:onClick="click" />
    
      <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="调用c代码,加法"
        android:onClick="clickAdd" />
      
        <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="调用c代码,打印String"
        android:onClick="clickStrng" />

</LinearLayout>

package com.devchina.ndk4;

public class DevchinaProvider {
	static  {
		System.loadLibrary("devchina");
	}
	
	public native void cCallJava(); 
	public native void cCallString();
	public native int  cCallAdd();
	
	
	//1.调用java空方法
	public void callJava(){
		System.out.println("i come from java");
	}

	public int add(int x,int y){
		System.out.println("devchina java res = "+(x+y));
		return x+y;
	}
	
	public void printString(String s){
		System.out.println("devchina java "+ s);
	}
}

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