本博客主要是在Ubuntu 下開發,且默認你已經安裝了Eclipse,Android SDK, Android NDK, CDT插件。java
在Eclipse中添加配置NDK,路徑以下Eclipse->Window->Preferences->Android->NDK ,選擇NDK的路徑,而後Apply便可。android
新建一個名爲AndroidJNI_Object的Android工程,新建一個jni的文件夾,其目錄下文件樹列表以下:數組
├── jni
│ ├── Android.mk
│ ├── Application.mk
│ └── object
│ ├── Android.mk
│ ├── logger.h
│ └── object_jni.capp
jni/Application.mk文件內容以下:ide
APP_ABI := all
jni/Android.mk,主要用來指定順序執行全部子文件夾下面的makefile文件,內容以下:函數
include $(call all-subdir-makefiles)
jni/object/Android.mk,主要用來指定須要編譯出的動態庫的名稱,以及須要編譯的源文件,內容以下:spa
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := object_jni LOCAL_SRC_FILES := object_jni.c LOCAL_LDLIBS := -llog include $(BUILD_SHARED_LIBRARY)
jni/object/logger.h 主要用來在JNI層打印日誌,內容以下:插件
#include <jni.h> #include <android/log.h> /** * 定義log標籤 */ #define TAG "jni_logger" /** * 定義info信息 */ #define LOGI(...) __android_log_print(ANDROID_LOG_INFO, TAG, __VA_ARGS__) /** * 定義debug信息 */ #define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, TAG, __VA_ARGS__) /** * 定義error信息 */ #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, TAG, __VA_ARGS__)
jni/object/object_jni.c,主要用來註冊綁定java函數和native函數,以及java函數在c中相應函數的具體實現, 內容以下:debug
#include "logger.h" #ifndef NULL #define NULL ((void *) 0) #endif /** * 獲取數組的大小 */ #define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0]))) /** * 指定要註冊的類,對應的完整的java類名 */ #define JNIREG_CLASS "com/clarck/jni/MainActivity" #define JNIPAR_CLASS "com/clarck/jni/Person" struct PersonOffsets { jfieldID name; jfieldID age; jfieldID height; } gPersonOffsets; typedef struct tagPerson { char mName[10]; int mAge; float mHeight; } Person; static Person gPersons[] = { {"clarck", 25, 175}, {"lilei", 30, 166}, {"hanmeimei", 51, 172}, }; #define GPERSON_NUM NELEM(gPersons) JNIEXPORT jint JNICALL native_object(JNIEnv *env, jobject clazz, jobject person, jint index) { if ((int) index < 0 || (int) index >= GPERSON_NUM) return -1; //將Person數組中的第index個成員賦值給pPerson指針 Person *pPerson = &gPersons[index]; //設置java對象的person的mName jstring name = (*env)->NewStringUTF(env, pPerson->mName); (*env)->SetObjectField(env, person, gPersonOffsets.name, name); //設置java對象person的mAge (*env)->SetIntField(env, person, gPersonOffsets.age, pPerson->mAge); //設置java對象person的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); return 0; } static void nativeClassInit(JNIEnv *env) { jclass personClass = (*env)->FindClass(env, JNIPAR_CLASS); gPersonOffsets.name = (*env)->GetFieldID(env, personClass, "mName", "Ljava/lang/String;"); gPersonOffsets.age = (*env)->GetFieldID(env, personClass, "mAge", "I"); gPersonOffsets.height = (*env)->GetFieldID(env, personClass, "mHeight", "F"); } /** * Java和JNI函數綁定 */ static JNINativeMethod method_table[] = { { "getPersonInfoByIndex", "(Lcom/clarck/jni/Person;I)I", (void*) native_object }, }; /** * 註冊native方法到java中 */ static int registerNativeMethods(JNIEnv* env, const char* className, JNINativeMethod* gMethods, int numMethods) { jclass clazz; clazz = (*env)->FindClass(env, className); if (clazz == NULL) { return JNI_FALSE; } if ((*env)->RegisterNatives(env, clazz, gMethods, numMethods) < 0) { return JNI_FALSE; } return JNI_TRUE; } /** * 調用註冊方法 */ int register_ndk_load(JNIEnv* env) { nativeClassInit(env); return registerNativeMethods(env, JNIREG_CLASS, method_table, NELEM(method_table)); } 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; } register_ndk_load(env); //返回jni的版本 return JNI_VERSION_1_4; }
接着在Project中右鍵Android Tools->Add Native Support,最後java層調用以下:指針
package com.clarck.jni; import android.app.Activity; import android.os.Bundle; import android.util.Log; public class MainActivity extends Activity { private Person mPerson = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Log.d("Test", "onCreate"); mPerson = new Person(); for (int i = 0; i < 3; i++) { getPersonInfoByIndex(mPerson, i); Log.d("Test", "mPersion[" + i + "] -- " + mPerson); } } private native int getPersonInfoByIndex(Person person, int index); static { System.loadLibrary("object_jni"); } }
package com.clarck.jni; public class Person { private String mName; private int mAge; private float mHeight; @Override public String toString() { return "mName: " + mName + ", mAge: " + mAge + ", mHeight: " + mHeight; } }
運行結果以下:
04-15 15:37:30.916: D/Test(31477): onCreate
04-15 15:37:30.916: D/jni_logger(31477): native_object index-0 mName:clarck, mAge:25, mHeight:175.000000
04-15 15:37:30.916: D/Test(31477): mPersion[0] -- mName: clarck, mAge: 25, mHeight: 175.0
04-15 15:37:30.916: D/jni_logger(31477): native_object index-1 mName:lilei, mAge:30, mHeight:166.000000
04-15 15:37:30.916: D/Test(31477): mPersion[1] -- mName: lilei, mAge: 30, mHeight: 166.0
04-15 15:37:30.916: D/jni_logger(31477): native_object index-2 mName:hanmeimei, mAge:51, mHeight:172.000000
04-15 15:37:30.916: D/Test(31477): mPersion[2] -- mName: hanmeimei, mAge: 51, mHeight: 172.0