android NDK 实用学习（一）-获取java端类及其类变量

近期为android 端项目包装一些c++代码，故学习ndk相关知识，现总结如下：

1，java与c++类型参照图：

2，此测试中使用的java类：

 package com.dasea.test.core;
 public class TestSetData {
     // 主要是类ID和字段ID，方法ID的缓存
     static {
         OnNative();
     }

     public native static void OnNative();

     public boolean bData;
     public double  dData;
     public int     iData;
     public byte    cData;
     public String  sData;
     public byte    byteArr[];

     public int     intArr[];

     public TestSetData() {
         // TODO Auto-generated constructor stub
         bData = true;
         dData = 100.11;
         iData = 333;
         cData = 100;
         sData = "20150204";
         byteArr = new byte[10];
         for (int i = 0; i < byteArr.length; i++) {
             byteArr[i] = '2';
         }

         intArr = new int[10];
         for (int i = 0; i < intArr.length; i++) {
             intArr[i] = i * 10;
         }
     }
 }

3，使用类接口定义：

①java端：

　　public native TestSetData testData(TestSetData obj);

②c++端：

　　 JNIEXPORT jobject JNICALL Java_com_dasea_test_core_JniDemo_testData(JNIEnv* env, jobject obj, jobject jobj) ;

4,完整c++端接口实现：

 JNIEXPORT jobject JNICALL Java_com_dasea_test_core_JniDemo_testData(JNIEnv* env, jobject obj, jobject jobj){
     DEBUG_OUT("test set data start");

     jclass jcSetDataMgr = env->FindClass("com/dasea/test/core/TestSetData");
     if(NULL == jcSetDataMgr){
         DEBUG_OUT("Not find class!");
         return NULL;
     }
     DEBUG_OUT("Find class succ!");

     jfieldID jfbdata = env->GetFieldID(jcSetDataMgr, "bData", "Z");
     if(NULL == jfbdata){
         DEBUG_OUT("jfbdata fail!");
     }
     jfieldID jfddata = env->GetFieldID(jcSetDataMgr, "dData", "D");
     if(NULL == jfbdata){
         DEBUG_OUT("jfddata fail!");
     }
     jfieldID jfidata = env->GetFieldID(jcSetDataMgr, "iData", "I");
     if(NULL == jfbdata){
         DEBUG_OUT("jfidata fail!");
     }
     jfieldID jfcdata = env->GetFieldID(jcSetDataMgr, "cData", "B");
     if(NULL == jfbdata){
         DEBUG_OUT("jfcdata fail!");
     }
     jfieldID jfsdata = env->GetFieldID(jcSetDataMgr, "sData", "Ljava/lang/String;");
     if(NULL == jfbdata){
         DEBUG_OUT("jfsdata fail!");
     }

     DEBUG_OUT("Get end!");

     env->SetBooleanField(jobj, jfbdata, false);
     DEBUG_OUT("SetBooleanField end!");

     env->SetDoubleField(jobj, jfddata, 209.22);
     DEBUG_OUT("SetDoubleField end!");

     env->SetIntField(jobj, jfidata, );
     DEBUG_OUT("SetIntField end!");

     env->SetByteField(jobj, jfcdata, );
     DEBUG_OUT("Set field succ!");

     char data[] = "";
     env->SetObjectField(jobj, jfsdata, env->NewStringUTF(data));

     jfieldID jiarr = env->GetFieldID(jcSetDataMgr, "intArr", "[I");
     if(NULL == jiarr){
         DEBUG_OUT("jfbdata fail!");
     }

     // 获取Java中数组属性arrays的对象
     jintArray jint_arr = (jintArray)env->GetObjectField(jobj, jiarr);

     int arrInt[] = {};
     for(int i = ; i < ; ++i){
        arrInt[i] = +i;
     }
     env->SetIntArrayRegion(jint_arr, , , arrInt);

     jfieldID jbyteArr = env->GetFieldID(jcSetDataMgr, "byteArr", "[B");
     char arrByte[] = "";
     jbyteArray jbyte_arr = (jbyteArray)env->GetObjectField(jobj, jbyteArr);
     env->SetByteArrayRegion(jbyte_arr, , , (const signed char*)arrByte);

     DEBUG_OUT("test set data end!");

     return NULL;
 }

5，单独讲解：

①查找java类：

jclass jcSetDataMgr = env->FindClass("com/dasea/test/core/TestSetData");

②查找类成员变量：

 jfieldID jfbdata = env->GetFieldID(jcSetDataMgr, "bData", "Z");
 jfieldID jfddata = env->GetFieldID(jcSetDataMgr, "dData", "D");
 jfieldID jfidata = env->GetFieldID(jcSetDataMgr, "iData", "I");
 jfieldID jfcdata = env->GetFieldID(jcSetDataMgr, "cData", "B");
 jfieldID jfsdata = env->GetFieldID(jcSetDataMgr, "sData", "Ljava/lang/String;");
 jfieldID jbyteArr = env->GetFieldID(jcSetDataMgr, "byteArr", "[B"