android112 jni 把java的字符串转换成c的字符串，数组处理

package com.itheima.charencode;

import android.os.Bundle;

import android.app.Activity;

import android.view.Menu;

import android.view.View;

import android.widget.EditText;

public class MainActivity extends Activity {

    private EditText et;

    static{

        System.loadLibrary("hello");//导入类库

    }

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        et = (EditText) findViewById(R.id.et);

    }

    public void click1(View v){

        String text = et.getText().toString();

        et.setText(encode(text, text.length()));

    }

    public void click2(View v){

        String text = et.getText().toString();

        et.setText(decode(text, text.length()));

    }

    public native String encode(String text, int length);

    public native String decode(String text, int length);

}

#include <jni.h>

#include <string.h>

//把java的字符串转换成c的字符串

char*   Jstring2CStr(JNIEnv*   env,   jstring   jstr)

{

     char*   rtn   =   NULL;

     jclass   clsstring   =   (*env)->FindClass(env,"java/lang/String");

     jstring   strencode   =   (*env)->NewStringUTF(env,"GB2312");

     jmethodID   mid   =   (*env)->GetMethodID(env,clsstring,   "getBytes",   "(Ljava/lang/String;)[B");

     jbyteArray   barr=   (jbyteArray)(*env)->CallObjectMethod(env,jstr,mid,strencode); // String .getByte("GB2312");

     jsize   alen   =   (*env)->GetArrayLength(env,barr);

     jbyte*   ba   =   (*env)->GetByteArrayElements(env,barr,JNI_FALSE);

     if(alen   >   )

     {

      rtn   =   (char*)malloc(alen+);         //"\0"

      memcpy(rtn,ba,alen);

      rtn[alen]=;

     }

     (*env)->ReleaseByteArrayElements(env,barr,ba,);  //

     return rtn;

}

JNIEXPORT jstring JNICALL Java_com_itheima_charencode_MainActivity_encode

  (JNIEnv * env, jobject obj, jstring jstr, jint lenght){

    char* cstr = Jstring2CStr(env, jstr);

    int i;

    for(i = ;i < lenght; i++){

        *(cstr + i) += ;

    }

    return (*env)->NewStringUTF(env, cstr);

}

/*

 * Class:     com_itheima_charencode_MainActivity

 * Method:    decode

 * Signature: (Ljava/lang/String;)Ljava/lang/String;

 */

JNIEXPORT jstring JNICALL Java_com_itheima_charencode_MainActivity_decode

(JNIEnv * env, jobject obj, jstring jstr, jint lenght){

    char* cstr = Jstring2CStr(env, jstr);

        int i;

        for(i = ;i < lenght; i++){

            *(cstr + i) -= ;

        }

        return (*env)->NewStringUTF(env, cstr);

}

数组处理：

package com.itheima.array;

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");

    }

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }

    int[] arr = {,,,,};

    public void click(View v){

        arrayEncode(arr);

        for (int i : arr) {//上面已经对数组内存进行了改变，所以此处是修改后的数组

            System.out.println(i);

        }

    }

    public native void arrayEncode(int[] arr);

}

/*

hello.c文件：

#include <jni.h>

JNIEXPORT void JNICALL Java_com_itheima_array_MainActivity_arrayEncode

  (JNIEnv * env, jobject obj, jintArray jintarr){//jintArray是整型数组，jni中所有的数组都是指针类型

    //拿到整型数组的长度以及第0个元素的地址

     //jsize  (*GetArrayLength)(JNIEnv*, jarray);jsize就是int类型（jni.h文件都有定义）

    int length = (*env)->GetArrayLength(env, jintarr);

     //jint*  (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);jint就是int类型

    int* arrp = (*env)->GetIntArrayElements(env, jintarr, 0);//得到第0个元素的地址

    int i;

    for(i = 0;i < length; i++){//数组是连续的内存空间，有了数组长度和数组第0个元素地址就相当于拿到了所有数组。

        *(arrp + i) += 10;//每个元素加10

    }

}*/