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：

 1 package com.dasea.test.core;
 2 public class TestSetData {
 3     // 主要是类ID和字段ID，方法ID的缓存
 4     static {
 5         OnNative();
 6     }
 7 
 8     public native static void OnNative();
 9 
10     public boolean bData;
11     public double  dData;
12     public int     iData;
13     public byte    cData;
14     public String  sData;
15     public byte    byteArr[];
16 
17     public int     intArr[];
18 
19     public TestSetData() {
20         // TODO Auto-generated constructor stub
21         bData = true;
22         dData = 100.11;
23         iData = 333;
24         cData = 100;
25         sData = "20150204";
26         byteArr = new byte[10];
27         for (int i = 0; i < byteArr.length; i++) {
28             byteArr[i] = '2';
29         }
30 
31         intArr = new int[10];
32         for (int i = 0; i < intArr.length; i++) {
33             intArr[i] = i * 10;
34         }
35     }
36 }

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：

 1 JNIEXPORT jobject JNICALL Java_com_dasea_test_core_JniDemo_testData(JNIEnv* env, jobject obj, jobject jobj){
 2     DEBUG_OUT("test set data start");
 3 
 4     jclass jcSetDataMgr = env->FindClass("com/dasea/test/core/TestSetData");
 5     if(NULL == jcSetDataMgr){
 6         DEBUG_OUT("Not find class!");
 7         return NULL;
 8     }
 9     DEBUG_OUT("Find class succ!");
10 
11     jfieldID jfbdata = env->GetFieldID(jcSetDataMgr, "bData", "Z");
12     if(NULL == jfbdata){
13         DEBUG_OUT("jfbdata fail!");
14     }
15     jfieldID jfddata = env->GetFieldID(jcSetDataMgr, "dData", "D");
16     if(NULL == jfbdata){
17         DEBUG_OUT("jfddata fail!");
18     }
19     jfieldID jfidata = env->GetFieldID(jcSetDataMgr, "iData", "I");
20     if(NULL == jfbdata){
21         DEBUG_OUT("jfidata fail!");
22     }
23     jfieldID jfcdata = env->GetFieldID(jcSetDataMgr, "cData", "B");
24     if(NULL == jfbdata){
25         DEBUG_OUT("jfcdata fail!");
26     }
27     jfieldID jfsdata = env->GetFieldID(jcSetDataMgr, "sData", "Ljava/lang/String;");
28     if(NULL == jfbdata){
29         DEBUG_OUT("jfsdata fail!");
30     }
31 
32     DEBUG_OUT("Get end!");
33 
34     env->SetBooleanField(jobj, jfbdata, false);
35     DEBUG_OUT("SetBooleanField end!");
36 
37     env->SetDoubleField(jobj, jfddata, 209.22);
38     DEBUG_OUT("SetDoubleField end!");
39 
40     env->SetIntField(jobj, jfidata, 3653);
41     DEBUG_OUT("SetIntField end!");
42 
43     env->SetByteField(jobj, jfcdata, 67);
44     DEBUG_OUT("Set field succ!");
45 
46     char data[10] = "4611354";
47     env->SetObjectField(jobj, jfsdata, env->NewStringUTF(data));
48 
49     jfieldID jiarr = env->GetFieldID(jcSetDataMgr, "intArr", "[I");
50     if(NULL == jiarr){
51         DEBUG_OUT("jfbdata fail!");
52     }
53 
54     // 获取Java中数组属性arrays的对象
55     jintArray jint_arr = (jintArray)env->GetObjectField(jobj, jiarr);
56 
57     int arrInt[10] = {0};
58     for(int i = 0; i < 10; ++i){
59        arrInt[i] = 220+i;
60     }
61     env->SetIntArrayRegion(jint_arr, 0, 10, arrInt);
62 
63     jfieldID jbyteArr = env->GetFieldID(jcSetDataMgr, "byteArr", "[B");
64     char arrByte[10] = "20200825";
65     jbyteArray jbyte_arr = (jbyteArray)env->GetObjectField(jobj, jbyteArr);
66     env->SetByteArrayRegion(jbyte_arr, 0, 8, (const signed char*)arrByte);
67 
68     DEBUG_OUT("test set data end!");
69 
70     return NULL;
71 }

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：

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

转载于:https://www.cnblogs.com/dhf-0214/p/4612618.html