Passing data to C language using JNI java

1. first, create the DataProvider class: [java] package com. pl. ndkpassdata; public class DataProvider {static {System. loadLibrary ("passdata"); // Load Library}/*** pass the int values in two java classes to the C language. After the C language completes processing, return the added result to java */public native int add (int x, int y ); /*** return the result of the C language processing subtraction operation to java */public static native int sub (int x, int y ); /*** pass the string in java to the C language. After the C language obtains the string in java, add a hello string */public native String getHell to the string. OString (String s);/*** pass an int array in java to the C language. After the C language completes processing this java array * add each element in the int array to + 10, then return the result to java */public native int [] getIntArr (int [] iNum);} 2. find it after creation. class: com_pl_ndkpassdata_DataProvider.h: [java]/* do not edit this file-it is machine generated */# include <JNI. h>/* Header for class com_pl_ndkpassdata_DataProvider */# ifndef _ Included_com_pl_ndkpassdata_DataProvider # define _ Included_com_pl_ndkpassdata_DataProvider # ifdef _ cplusplus extern "C" {# endif/** Class: com_pl_ndkpassdata_DataProvider * Method: add * Signature: (II) I */JNIEXPORT jint JNICALL inline (JNIEnv *, jobject, jint, jint);/** Class: com_pl_ndkpassdata_DataProvider * Method: sub * Signature: (II) I */JNIEXPORT jint JNICALL Java_com_pl_ndkpassdata_DataProvider_su B (JNIEnv *, jclass, jint, jint);/** Class: com_pl_ndkpassdata_DataProvider * Method: getHelloString * Signature: (Ljava/lang/String;) Ljava/lang/String; */JNIEXPORT jstring JNICALL values (JNIEnv *, jobject, jstring);/** Class: Optional * Method: getIntArr * Signature: ([I) [I */JNIEXPORT jintArray JNICALL values Data_DataProvider_getIntArr (JNIEnv *, jobject, jintArray); # ifdef _ cplusplus} # endif # The above is generated using the javah-jni command. 3. create a jni directory in the root directory of the project (level-1 with directories such as src and bin); 1. copy com_pl_ndkpassdata_DataProvider.h to the jni directory; 2. create Android in the jni directory. mk file and passdata. c file; (for c language. c and. the difference between the H file is that the function definition should be placed in. c, and. h only declares .) the following is Android. mk content: [java] LOCAL_PATH: = $ (call my-dir) include $ (CLEAR_VARS) LOCAL_MODULE: = passdata LOCAL_SRC_FILES: = passdata. c # liblog. c LOCAL_LDLIBS + =-llog include $ (BUILD_SHARED_LIBRARY) the following is passdata. c [java] # include <stdio. h> # include <Jni. h> # include <stdlib. h> # include "com_pl_ndkpassdata_DataProvider.h" # include <android/log. h> # define LOG_TAG "System. out. c "# define LOGD (...) _ android_log_print (ANDROID_LOG_DEBUG, LOG_TAG, _ VA_ARGS _) # define LOGI (...) _ android_log_print (ANDROID_LOG_INFO, LOG_TAG, _ VA_ARGS __) /*** converts a String in java to a pointer type that can point to a character in c. *** <jni. h> pointer function in: * jclass (* FindClass) (JNIEnv *, const char *); // get Class * jstring (* NewStringUTF) (JNIEnv *, const char *); // get a String object * jmethodID (* GetMethodID) (JNIEnv *, jclass, const char *, const char *); // method for getting the class * jobject (* CallObjectMethod) (JNIEnv *, jobject, jmethodID ,...); // call the Class Method * jsize (* GetArrayLength) (JNIEnv *, jarray); // obtain the array length * jbyte * (* GetByteArrayElements) (JNIEnv *, jbyteArray, jboolean *); // converts to byte pointer types available for c */char * Jstring2CStr (JNIEnv * env, jstring s ){ // JNIEnv *: pointer of the C language implementation of the struct structure of the Java Virtual Machine, including many jni Methods char * rtn = NULL; jclass classstring = (* env)-> FindClass (env, "java/lang/String"); // call the String class jstring strencode = (* env) in java-> NewStringUTF (env, "GB2312 "); // obtain the encoding format // obtain the method. Parameter 2: Specifies the class, parameter 3: method name, parameter 4 :( Ljava/lang/String;) is the parameter of getBytes; [B indicates that the returned value is a byte array jmethodID mid = (* env)-> GetMethodID (env, classstring, "getBytes", "(Ljava/lang/String ;) [B "); jbyteArray barr = (jbyteArray) (* env)-> CallObjectMethod (env, s, mid, strencode ); // equivalent to calling java's getBytes // get the length of the byte array jsize size = (* env)-> GetArrayLength (env, barr); jbyte * ba = (* env) -> GetByteArrayElements (env, barr, JNI_FALSE); if (size> 0) {rtn = (Char *) malloc (size + 1); // apply for a piece of memory // + "\ 0" memcpy (rtn, ba, size ); // copy the string rtn [size] = 0; // '\ 0'} (* env)-> ReleaseByteArrayElements (env, barr, ba, 0 ); // release the memory space return rtn;} JNIEXPORT jint JNICALL encode (JNIEnv * env, jobject obj, jint x, jint y) {LOGD ("add () x: % d, y: % d ", x, y); return x + y;} JNIEXPORT jint JNICALL Java_com_pl_ndkpassdata_DataProvider_sub (JNIEnv * env, jclass c Lazz, jint x, jint y) {LOGD ("sub () x: % d, y: % d", x, y); return x-y ;} JNIEXPORT jstring JNICALL values (JNIEnv * env, jobject obj, jstring s) {char * cs = Jstring2CStr (env, s); LOGD ("cs = % s", cs ); char carr [7] = {'', 'h', 'E', 'l', 'l', 'O', '\ 0'}; strcat (cs, carr); // concatenate LOGD ("new cs = % s", cs); LOGD ("end getHelloString ()"); return (* env)-> NewStringUTF (env, cs);} // jsize (* GetArrayLength) (JNIEnv *, jarray); // get the array length // jint * (* GetIntArrayElements) (JNIEnv *, jintArray, jboolean *) // convert to c available int pointer type JNIEXPORT jintArray JNICALL struct (JNIEnv * env, jobject obj, jintArray jarr) {jsize len = (* env)-> GetArrayLength (env, jarr); LOGD ("len = % d", len); jint * carr = (* env)-> GetIntArrayElements (env, jarr, JNI_FALSE); int I; for (I = 0; I <len; I ++ ){ * (Carr + I) + = 10;} LOGD ("end getIntArr ()"); return jarr;} ing implementation, which is generated using Cygwin. so library file. it's almost done. Don't forget to clean the project. Basically, this is done. The following is the test code: MainActivity. java [java] package com. pl. ndkpassdata; import android. OS. bundle; import android. app. activity; import android. view. view; import android. view. view. onClickListener; import android. widget. button; import android. widget. toast; public class MainActivity extends Activity implements OnClickListener {private Button bt1, bt2, bt3, bt4; private DataProvider provider; @ Override protected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. main); bt1 = (Button) this. findViewById (R. id. bt1); bt2 = (Button) this. findViewById (R. id. bt2); bt3 = (Button) this. findViewById (R. id. bt3); bt4 = (Button) this. findViewById (R. id. bt4); bt1.setOnClickListener (this); bt2.setOnClickListener (this); bt3.setOnClickListener (this); bt4.setOnClickListener (this); provider = new DataProvider ();} public void onClick (View v) {switch (v. getId () {case R. id. bt1: int result = provider. add (10, 10); Toast. makeText (this, "added result:" + result, 1 ). show (); break; case R. id. bt2: String str = provider. getHelloString ("pengliang"); Toast. makeText (this, str, 1 ). show (); break; case R. id. bt3: int [] arr = {7, 8, 9, 10, 6}; provider. getIntArr (arr); String arrtostr = "["; for (int I = 0; I <arr. length; I ++) {arrtostr + = arr [I] + "," ;}arrtostr + = "]"; Toast. makeText (this, arrtostr, 1 ). show (); break; case R. id. bt4: int subresult = DataProvider. sub (100, 24); Toast. makeText (this, "subtraction Result:" + subresult, 1 ). show (); break ;}} main. xml: [java] <LinearLayout xmlns: android = "http://schemas.android.com/apk/res/android" android: layout_width = "fill_parent" android: layout_height = "fill_parent" android: orientation = "vertical"> <Button android: id = "@ + id/bt1" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "pass two intors to c code"/> <Button android: id = "@ + id/bt2" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "Pass string to c code"/> <Button android: id = "@ + id/bt3" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "pass the int array to the c code"/> <Button android: id = "@ + id/bt4" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "Call static native METHOD"/> </LinearLayout>