Android技术10：Java与C语言之间简单数据的传递

1 package com.forsta.ndk;
2 
3 public class NativeClass {
4     public native int add(int x,int y);
5     public native String showString(String str);
6     public native int[] array(int [] a);
7     public static native int sub(int x,int y);
8 }

 1 /* DO NOT EDIT THIS FILE - it is machine generated */
 2 #include <jni.h>
 3 /* Header for class com_forsta_ndk_NativeClass */
 4 
 5 #ifndef _Included_com_forsta_ndk_NativeClass
 6 #define _Included_com_forsta_ndk_NativeClass
 7 #ifdef __cplusplus
 8 extern "C" {
 9 #endif
10 /*
11  * Class:     com_forsta_ndk_NativeClass
12  * Method:    add
13  * Signature: (II)I
14  */
15 JNIEXPORT jint JNICALL Java_com_forsta_ndk_NativeClass_add
16   (JNIEnv *, jobject, jint, jint);
17 
18 /*
19  * Class:     com_forsta_ndk_NativeClass
20  * Method:    showString
21  * Signature: (Ljava/lang/String;)Ljava/lang/String;
22  */
23 JNIEXPORT jstring JNICALL Java_com_forsta_ndk_NativeClass_showString
24   (JNIEnv *, jobject, jstring);
25 
26 /*
27  * Class:     com_forsta_ndk_NativeClass
28  * Method:    array
29  * Signature: ([I)[I
30  */
31 JNIEXPORT jintArray JNICALL Java_com_forsta_ndk_NativeClass_array
32   (JNIEnv *, jobject, jintArray);
33 
34 /*
35  * Class:     com_forsta_ndk_NativeClass
36  * Method:    sub
37  * Signature: (II)I
38  */
39 JNIEXPORT jint JNICALL Java_com_forsta_ndk_NativeClass_sub
40   (JNIEnv *, jclass, jint, jint);
41 
42 #ifdef __cplusplus
43 }
44 #endif
45 #endif

 1 #include <stdio.h>
 2 #include <jni.h>
 3 #include<malloc.h>
 4 #include "com_forsta_ndk_NativeClass.h"
 5 
 6 
 7 /**
 8  * 返回值 char* 这个代表char数组的首地址
 9  *  Jstring2CStr 把java中的jstring的类型转化成一个c语言中的char 字符串
10  */
11 char*   Jstring2CStr(JNIEnv*   env,   jstring   jstr)
12 {
13      char*   rtn   =   NULL;
14      jclass   clsstring   =   (*env)->FindClass(env,"java/lang/String"); //String
15      jstring   strencode   =   (*env)->NewStringUTF(env,"GB2312");  // 得到一个java字符串 "GB2312"
16      jmethodID   mid   =   (*env)->GetMethodID(env,clsstring,   "getBytes",   "(Ljava/lang/String;)[B"); //[ String.getBytes("gb2312");
17      jbyteArray   barr=   (jbyteArray)(*env)->CallObjectMethod(env,jstr,mid,strencode); // String .getByte("GB2312");
18      jsize   alen   =   (*env)->GetArrayLength(env,barr); // byte数组的长度
19      jbyte*   ba   =   (*env)->GetByteArrayElements(env,barr,JNI_FALSE);
20      if(alen   >   0)
21      {
22       rtn   =   (char*)malloc(alen+1);         //"\0"
23       memcpy(rtn,ba,alen);
24       rtn[alen]=0;
25      }
26      (*env)->ReleaseByteArrayElements(env,barr,ba,0);  //
27      return rtn;
28 }
29 
30 JNIEXPORT jint JNICALL Java_com_forsta_ndk_NativeClass_add
31   (JNIEnv *env, jobject obj, jint x, jint y){
32     return x+y;
33 }
34 
35 JNIEXPORT jstring JNICALL Java_com_forsta_ndk_NativeClass_showString
36   (JNIEnv *env, jobject obj, jstring str){
37     //c语言中没有String类型
38     char* s=Jstring2CStr(env,str);
39     //c语言中的字符串 都是以‘/0‘ 作为结尾
40     char s1[7]={‘ ‘,‘h‘,‘e‘,‘l‘,‘l‘,‘o‘,‘\0‘};
41     strcat(s,s1);
42     return (*env)->NewStringUTF(env,s);
43 }
44 
45 JNIEXPORT jintArray JNICALL Java_com_forsta_ndk_NativeClass_array
46   (JNIEnv *env, jobject obj, jintArray arr){
47     //1。获取数组长度
48     //2.修改每个数据
49     int size=(*env)->GetArrayLength(env,arr);
50     int * array=(*env)->GetIntArrayElements(env,arr,0);
51     int i=0;
52     for(;i<size;i++){
53         array[i]+=10;
54     }
55     return arr;
56 
57 }
58 JNIEXPORT jint JNICALL Java_com_forsta_ndk_NativeClass_sub
59   (JNIEnv *env, jclass clazz, jint x, jint y){
60     return x-y;
61 }

 1     @Override
 2     public void onClick(View v) {
 3         int id =v.getId();
 4         switch (id) {
 5         case R.id.bt1:
 6             int result=nativeClass.add(10, 90);
 7             Toast.makeText(getApplicationContext(), "显示结果："+result, Toast.LENGTH_SHORT).show();
 8             break;
 9         case R.id.bt2:
10             Toast.makeText(getApplicationContext(), nativeClass.showString("Forsta"), Toast.LENGTH_SHORT).show();
11             break;
12         case R.id.bt3:
13             int [] arr={1,2,3,4,5};
14             nativeClass.array(arr);
15             String s = "";
16             for(int i:arr){
17                 s+=i+" ";
18             }
19             Toast.makeText(getApplicationContext(),s,Toast.LENGTH_SHORT).show();
20             break;
21         case R.id.bt4:
22             int result1=NativeClass.sub(90, 10);
23             Toast.makeText(getApplicationContext(), "相减显示结果："+result1, Toast.LENGTH_SHORT).show();
24             break;
25         default:
26             break;
27         }
28         
29     }