JNI转换接口

最新推荐文章于 2021-03-19 18:54:23 发布

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最新推荐文章于 2021-03-19 18:54:23 发布

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本文链接：https://blog.youkuaiyun.com/woshi750814343/article/details/49534507

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本文主要介绍了作者在学习和使用JNI转换Android接口过程中的经验，从完全不懂到逐步理解，详细记录了结构体信息和获取类信息的关键步骤。

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最近在写JNI转换Android接口，我是完全不懂，照着别人的套路写，现在总结一下

结构体信息入下：

struct PICTURECFG
{
	BYTE byUseType;
	BASEMAP_CFG struBasemapCfg;
	BYTE[NAME_LEN] sPicName;
	int dwVideoWallNo;
};

struct BASEMAP_CFG
{
	BYTE byScreenIndex;
	int wSourWidth;
};

转换函数：

JNIEXPORT jint JNICALL Java_com_netsdk_HCNetSDK_NET_1DVR_1PicUpload
  (JNIEnv *env, jobject obj, jint lUserID, jstring sFileName, jobject oPictureCfg)
{
	if(oPictureCfg == NULL)
	{
		return -1;
	}
	if(!env->IsInstanceOf(oPictureCfg,env->FindClass("com/hikvision/netsdk/PICTURECFG")))
	{
		return -1;
	}

	jclass cPictureCfg = env->GetObjectClass(oPictureCfg);
	jfieldID idbyUseType = env->GetFieldID(cPictureCfg,"byUseType","B");
	jfieldID idstruBasemapCfg = env->GetFieldID(cPictureCfg,"struBasemapCfg","[Lcom/netsdk/BASEMAP_CFG;");
	jfieldID idsPicName = env->GetFieldID(cPictureCfg,"sPicName","[B");
	jfieldID iddwVideoWallNo = env->GetFieldID(cPictureCfg,"dwVideoWallNo","I");

	PICTURECFG struPicCfg = {0};
	struPicCfg.byUseType = env->GetByteField(oPictureCfg,idbyUseType);
	jbyteArray arrPicName = (jbyteArray)env->GetObjectField(oPictureCfg,idsPicName);
	env->GetByteArrayRegion(arrPicName,0,NAME_LEN,(jbyte*)struPicCfg.sPicName);
	struPicCfg.dwVideoWall = env->GetIntField(oPictureCfg,iddwVideoWallNo);

	jobject oBasemapCfg = env->GetObjectField(oPictureCfg,idstruBasemapCfg);
	jclass cBasemapCfg = env->GetObjectClass(oBasemapCfg);
	jfieldID idbyScreenIndex = env->GetFieldID(cBasemapCfg,"byScreenIndex","B");
	jfieldID idwSourWidth = env->GetFieldID(cBasemapCfg,"wSourWidth","I");

	struPicCfg.struBasemapCfg.byScreenIndex = env->GetByteField(oBasemapCfg,idbyScreenIndex);
	struPicCfg.struBasemapCfg.wSourWidth = env->GetIntField(oBasemapCfg,idwSourWidth);

	const char *strFileName = env->GetStringUTFChars(sFileName, 0);
	return  PicUpload(lUserID,strFileName,&struPicCfg);

}

1.首先判断类oPictureCfg是否为空，java里面是否定义了这个类

	if(oPictureCfg == NULL)
	{
		return -1;
	}
	if(!env->IsInstanceOf(oPictureCfg,env->FindClass("com/hikvision/netsdk/PICTURECFG")))
	{
		return -1;
	}

2.获取类信息

jclass cPictureCfg = env->GetObjectClass(oPictureCfg);

3.获取id信息（类的成员变量的id）

jfieldID idbyUseType = env->GetFieldID(cPictureCfg,"byUseType","B");

如果里面还有类的成员变量

jfieldID idstruBasemapCfg = env->GetFieldID(cPictureCfg,"struBasemapCfg","[Lcom/netsdk/BASEMAP_CFG;");

4.定义结构体并获取值

PICTURECFG struPicCfg = {0};
struPicCfg.byUseType = env->GetByteField(oPictureCfg,idbyUseType);

如有数组

jbyteArray arrPicName = (jbyteArray)env->GetObjectField(oPictureCfg,idsPicName);
env->GetByteArrayRegion(arrPicName,0,NAME_LEN,(jbyte*)struPicCfg.sPicName);

里面的类，在递归，获取object，获取class,获取id，获取值

jobject oBasemapCfg = env->GetObjectField(oPictureCfg,idstruBasemapCfg);
jclass cBasemapCfg = env->GetObjectClass(oBasemapCfg);
jfieldID idbyScreenIndex = env->GetFieldID(cBasemapCfg,"byScreenIndex","B");
jfieldID idwSourWidth = env->GetFieldID(cBasemapCfg,"wSourWidth","I");

struPicCfg.struBasemapCfg.byScreenIndex = env->GetByteField(oBasemapCfg,idbyScreenIndex);
struPicCfg.struBasemapCfg.wSourWidth = env->GetIntField(oBasemapCfg,idwSourWidth);

string转换为char*

const char *strFileName = env->GetStringUTFChars(sFileName, 0);

5.调用C++的函数

return  PicUpload(lUserID,strFileName,&struPicCfg);