Android 開發筆記 - 使用 Android NDK / JNI 回傳 HashMap 物件至 Java 端

C/C++ Code:

#include <jni.h>

extern "C" {

jobject Java_YourPackageName_getHashMap(JNIEnv *env, jobject thiz) {

    jclass mapClass = env->FindClass("java/util/HashMap");
    jmethodID obj_init = env->GetMethodID(mapClass, "<init>", "(I)V");
    jmethodID obj_put = env->GetMethodID(mapClass, "put", "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;");
    jobject hashMap = env->NewObject(mapClass, obj_init, 1);

    /*
    const char * input_data = "HelloWorld";
    int input_data_length = strlen(input_data);

    jbyteArray data = env->NewByteArray(input_data_length);
    env->SetByteArrayRegion(data, 0, input_data_length, (const jbyte *)input_data);
    env->CallObjectMethod(hashMap, obj_put, (jbyteArray)data, (jbyteArray)data);
    env->DeleteLocalRef(data);
    */
    jstring key = env->NewStringUTF("Hello");
    jstring value = env->NewStringUTF("World");
    env->CallObjectMethod(hashMap, obj_put, key, value);
    env->DeleteLocalRef(key);
    env->DeleteLocalRef(value);

    //env->DeleteLocalRef(hashMap);
    return hashMap;
}

}

Android Java code:

public native HashMap getHashMap();
static {
        System.loadLibrary("native");
}

void usage() {
HashMap<String, String> mHashMap = getHashMap();

        Log.d(tag, "HashMap size: "+mHashMap.size());
        Log.d(tag, "HashMap data with key(Hello): "+mHashMap.get("Hello"));
        Iterator it = mHashMap.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry pair = (Map.Entry)it.next();
            Log.d(tag, "HashMap key: ["+pair.getKey()+"], value: ["+pair.getValue().toString()+"]");
        }
}