android NDK 实用学习（一）-获取java端类及其类变量

向右看齐 2021-12-24 03:23 160阅读 0赞

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：

![1335772891_3871.jpg][]

![1335773449_4298.jpg][]

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

[1335772891_3871.jpg]: https://img-my.csdn.net/uploads/201204/30/1335772891_3871.jpg
[1335773449_4298.jpg]: https://img-my.csdn.net/uploads/201204/30/1335773449_4298.jpg