JNI Learning 2:android calls the C language method and calls the Android method with C language

#include <jni.h> #include <stdio.h> #include <stdlib.h> #include <jni.h> #include <android/ log.h> #define LOG_TAG "System.out"//log garbled when you set the project file encoding to Utf-8/**debug level log: Android_log_debug: level, Log_tag: tags, __va_ ARGS__: Log content) **/#define LOGD (...) __android_log_print (android_log_debug,log_tag,__va_args__)/**info level log: ANDROID_ Log_info: Level, Log_tag: tags, __va_args__: log content) **/#define Logi (...) __android_log_print (Android_log_info,log_tag,__va_ args__) extern "C" {/***java language string to C language char***/char* Jstringtochar (jnienv *env, jstring jstr) {char* RTN = Null;jclass cl asstring = Env->findclass ("java/lang/string"); jstring Strencode = Env->newstringutf ("GB2312"); JmethodID mid = Env->getmethodid (classtring, "GetBytes", "(ljava/lang/string;) [B"); Jbytearray Barr = (Jbytearray) env-> Callobjectmethod (Jstr, Mid, Strencode); Jsize alen = Env->getarraylength (Barr); jbyte* ba = env-> Getbytearrayelements (Barr, Jni_false); if (Alen > 0) {rtn = (char*) malloc (alen + 1); memcpy (RTN, BA, Alen); Rtn[alen] = 0;} Env->releasebytearrayelements (Barr, BA, 0); return RTN;} Jniexport jstring Java_com_example_ndktest_jniprovideer_hello (jnienv *env,jobject obj) {LOGD ("%s", "haha"); return Env->newstringutf ("Hello from JNI!");} /***2 integer Add ***/jniexport jint java_com_example_ndktest_jniprovideer_add (jnienv *env,jobject obj,jint x,jint y) {return X+y;} /*** string Conversion ***/jniexport jstring Java_com_example_ndktest_jniprovideer_sayhello (jnienv *env,jobject obj,jstring jstr) {char* P=jstringtochar (ENV,JSTR); Logi ("sss%s", p);//strcat (p,helloword) means Helloword? Stitching to P back Env->newstringutf (strcat (P, "Helloword"));} /*** an array of integers with each element plus 10***/jniexport Jintarray java_com_example_ndktest_jniprovideer_getintarray (JNIEnv *env,jobject obj, Jintarray Jintarr) {//Get array length int len=env->getarraylength (JINTARR);  Logi ("len=%d", Len);//get integer array address jint* arr=env->getintarrayelements (jintarr,0); for (int i=0; i < Len; i++) {* (arr+i) +=10;} return Jintarr;} /*** calls the Java object in the active method String getString () * () ljava/lang/string; indicates that the parameter is empty and the return value is sTring***/jniexport void java_com_example_ndktest_jniprovideer_getjavamethodforgetstring (JNIEnv *env,jobject obj) { Jclass Classz=env->findclass ("Com/example/ndktest/jniprovideer"), if (classz==0) {Logi ("Can ' t find Class");} Else{logi ("Find Class");} Jmethodid Javamethod=env->getmethodid (CLASSZ, "getString", "() ljava/lang/string;"); if (javamethod==0) {Logi ("can ' t find Menthod");}    Else{logi ("Find Menthod");} Jstring result= (jstring) Env->callobjectmethod (Obj,javamethod); char* P=jstringtochar (Env,result); Logi ("result=%s", p);} /*** the active call to the Java object in the method int getadd (int x,int y) * (II) I means the parameter is 2 integers, the return value is an integer ***/jniexport void java_com_example_ndktest_ Jniprovideer_getjavamethodforgetadd (jnienv *env,jobject obj) {jclass Classz=env->findclass ("Com/example/ndktest /jniprovideer "), if (classz==0) {Logi (" Can ' t find Class ");} Else{logi ("Find Class");} Jmethodid Javamethod=env->getmethodid (CLASSZ, "Getadd", "(II) I"), if (javamethod==0) {Logi ("can ' t find Menthod");} Else{logi ("Find Menthod");} int result= Env->callintmeThod (obj,javamethod,7,7); Logi ("result=%d", result);} /*** active call in Java object method void Getvoidmethod (String x) * (ljava/lang/string;) v for argument is String, return value is null ***/jniexport void Java_com_ Example_ndktest_jniprovideer_getjavamethodforgetvoidmethod (jnienv *env,jobject obj) {jclass classz=env-> Findclass ("Com/example/ndktest/jniprovideer"), if (classz==0) {Logi ("Can ' t find Class");} Else{logi ("Find Class");} Jmethodid Javamethod=env->getmethodid (CLASSZ, "Getvoidmethod", "(ljava/lang/string;) V"); if (javaMethod==0) {LOGI ("Can ' t find Menthod");} Else{logi ("Find Method");} Env->callvoidmethod (Obj,javamethod,env->newstringutf ("abc"));}}

　　

Package Com.example.ndktest;import Android.util.log;public class Jniprovideer {  static{  system.loadlibrary ( "Ndktest");  }  public native int Add (int x,int y);  Public native string SayHello (string s);  Public native int[] Getintarray (int[] ints);  Public native String hello ();  public native void Getjavamethodforgetstring ();  public native void Getjavamethodforgetadd ();  public native void Getjavamethodforgetvoidmethod ();  /**   * method to make the C language active call * @return */public String getString () {  return "Hello";  } /** * method to make the C language active call * @return *  /public int getadd (int x,int y) {  return x+y;  }  /**   * method to make the C language active call * @return */public    void Getvoidmethod (String x) {          log.i ("test", "Input value:" +x) ;    }}

　　

Package Com.example.ndktest;import Android.app.activity;import Android.os.bundle;import android.view.View;import Android.view.view.onclicklistener;import Android.widget.button;import Android.widget.toast;public Class Mainactivity extends Activity {public native String hello (); @Overrideprotected void OnCreate (Bundle savedinstancestate ) {super.oncreate (savedinstancestate); Setcontentview (R.layout.fragment_main); Button tx= (button) Findviewbyid (r.id.test) Tx.setonclicklistener (new Onclicklistener () {@Overridepublic void OnClick (View v) {Jniprovideer jniprovideer=new jniprovideer (); String result= "";//result=jniprovideer.hello ();//int Add=jniprovideer.add (4, 5);//result=add+ "";//int[] intarray= Jniprovideer.getintarray (New int[]{3,5,5,4});//for (int i = 0; i < intarray.length; i++) {//result+=intarray[i];//}// Result=jniprovideer.sayhello ("say:");//jniprovideer.getjavamethodforgetstring ();// Jniprovideer.getjavamethodforgetadd (); Jniprovideer.getjavamethodforgetvoidmethod ();//Toast.makeTExt (Getapplicationcontext (), result, 0). Show ();}});}} 

　　

JNI Learning 2:android calls the C language method and calls the Android method with C language