Android Jni and NDK Learning (--JNI) instance two pass-through class objects

1 Application Layer Code

Ndkparam.java is the invocation class for the JNI function, and its code is as follows:

PackageCOM.SKYWANG.NDK;Importandroid.app.Activity;ImportAndroid.os.Bundle;ImportAndroid.util.Log;PublicClass NdkparamExtendsActivity {PublicStaticFinal String tag= "Skywang--ndkparam";/**Called when the activity is first created.*/Private person person=Null; @OverridePublicvoidOnCreate (Bundle savedinstancestate) {Super. OnCreate (Savedinstancestate); Setcontentview (R.layout.main); LOG.D (TAG, "on Create.")); person = New Person (); for (int. i=0; i<3; i++) {Getpersoninfobyindex (person, i); LOG.D (TAG, "person[" +i+ "]--" + person ";}} method registered in// JNI private native int getpersoninfobyindex (person person, int index); static { // load local libndk_load.so library file system.loadlibrary ("Ndk_param");}}    

Person.java is the data class used to pass between Java and JNI, and its code is as follows:

Package COM.SKYWANG.NDK;  Class person {        privateintfloatpublicreturn ' mname: ' +mname+ ', MAge: ' +mage+ ', Mheight: "+Mheight;}}        

2 JNI Layer Code

NDK_PARAM.C is the file that implements and registers JNI, and its code is as follows:

#include <stdlib.h>#include <String.h>#include <stdio.h>#include <jni.h>#include <assert.h>//Gets the size of the array # define NELEM (x) (int) (sizeof (x)/sizeof ((x) [0])))//Specifies the class to register, corresponding to the full Java class name#define JNIREG_CLASS "Com/skywang/ndk/ndkparam"#define JNIPAR_CLASS "Com/skywang/ndk/person"//Introduction of log header file # include <android/log.h>//Log label#define TAG "Hello_param"//Defining Info Info#define Logi (...) __android_log_print (android_log_info,tag,__va_args__)//Defining debug information#define LOGD (...) __android_log_print (Android_log_debug, TAG, __va_args__)//Define error information#define LOGE (...) __android_log_print (android_log_error,tag,__va_args__)//Jfieldid structure for preserving the Filedid of class "Person.java"structpersonoffsets{jfieldid name; Jfieldid age; jfieldid height;} gpersonoffsets;//The structure corresponding to "Person.java", which holds the data and assigns the data to the member typedef of PERSON.JAVAstructtagperson{Char mname[10];IntMAge;FloatMheight;} person;//3 person definedstatic person gpersons[] ={ {"Skywang",25,175}, {"Eman" ,30,166}, {"Dan" ,41M172},};#define Gperson_num Nelem (gpersons)/** Get person information based on index. * Parameter Description: * ENV:JNI interface pointer. * Claszz:java class object. * Person: Input parameter, Java Object * Index: input parameter, serial number.*/Jniexport jint jnicall getpersoninfobyindex (jnienv *Env, Jobject clazz, jobject person, jint index) {//If index is invalid, returns 1 directly.if ((int) index<0 | | (int) index>=Gperson_num)Return-1;//Assigns the index member of the person Array (gpersons) to the Pperson pointer *pperson = &Gpersons[index];//Set the Java object mname jstring name = (*env)->newstringutf (env, pperson->Mname); (*env)Setobjectfield (env, person, gpersonoffsets.name, name);//Set Java Object Person's mage (*env)->setintfield (env, person, Gpersonoffsets.age, pperson->MAGE);//Set Java Object Person's mheight (*env)->setfloatfield (env, person, Gpersonoffsets.height, pperson->Mheight); LOGD ("%s index-%d mname:%s, mage:%d, mheight:%f\n", __func__, Index, Pperson->mname, Pperson->mage, pperson->Mheight);Return0;}//Initializes the function to obtain the corresponding FieldID for each member of the Java.Staticvoid Nativeclassinit (JNIENV *ENV) {Jclass Personclass = (*env)Findclass (env, jnipar_class);//Gets the mname member of the person corresponding to the FieldID, and saves it to gpersonoffsets gpersonoffsets.name = (*env)->getfieldid (env, Personclass,"Mname" ,"ljava/lang/string;");//Gets the mage member of the person corresponding to the FieldID, and saves it to gpersonoffsets gpersonoffsets.age = (*env)->getfieldid (env, Personclass,"MAge" ,"I");//Gets the mheight member of the person corresponding to the FieldID, and saves it to gpersonoffsets gpersonoffsets.height = (*env)->getfieldid (env, Personclass,"Mheight","F");}//Binding tables for Java and JNI functionsStatic Jninativemethod method_table[] ={ {"Getpersoninfobyindex","(Lcom/skywang/ndk/person;i) I", (void*) Getpersoninfobyindex},//Binding};//Registering the native method in JavaStaticint Registernativemethods (jnienv* env,Constchar*ClassName, jninativemethod* Gmethods,IntNummethods) {Jclass clazz; clazz = (*env)Findclass (env, className);if (Clazz = =NULL) {ReturnJni_false; }if (*env)->registernatives (env, Clazz, Gmethods, Nummethods) <0) {ReturnJni_false; }ReturnJni_true;}int Register_ndk_param (JNIENV *ENV) {nativeclassinit (env);//Calling the registration methodReturnregisternativemethods (env, Jnireg_class, method_table, Nelem (method_table));} // jni_onload when JNI is registered, it is executed by callback. Jniexport jint jni_onload (javavm* vm, void* reserved) {jnienv* env = NULL; jint result =-1; if (*VM)->getenv (VM, (void**) &env, jni_version_1_4)! = Jni_ok) { return result;} registe R_ndk_param (env); // return to JNI version return jni_version_1_4;}           

The code for ANDROID.MK is as follows:

Local_path: = $ (call my-dir) include $ (clear_vars) local_module    : = ndk_paramlocal_src_files: = ndk_ param.c# add support for the Log Library local_ldlibs:=-l$ (sysroot)/usr/lib-llog#  if a static. A is generated, simply add local_ldlibs:=-llog Include $ (build_shared_library) Local_path: = $ (call my-dir)      

3 Running the project

Logcat information is as follows:

d/skywang--Ndkparam:on Create. D/hello_param:getpersoninfobyindex index-0 Mname:skywang, MAge:Mheight:175.000000d/skywang--ndkparam:person[0]--Mname:skywang, MAge:mheight:175.0d/hello_param:getpersoninfobyindex index-1 Mname:eman, MAge: +, mheight : 166.000000d/skywang--ndkparam:person[1]--Mname:eman, MAge: +, mheight:166.0D/hello_param: Getpersoninfobyindex index-2 Mname:dan, MAge:Wuyi, Mheight:172.000000d/skywang--ndkparam:person[ 2]--Mname:dan, MAge:Wuyi, Mheight:172.0          

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Android Jni and NDK Learning (--JNI) instance two pass-through class objects