如何在不同的語言/平台中獲取Android ID#

最近開發工作中需要使用到AndroidID,在Unity和native code中也需要使用，java獲取很方便，Unity中也不難，最難的是在native code中獲取。

獲取android ID需要有一個上下文實例，也就是Context實例，看下面的java獲取方式：

在java中獲取##

Android原生代碼，這個是最簡單的：

public static String GetAndroid(Context context){
    final String androidId;
    androidId = android.provider.Settings.Secure.getString(context.getContentResolver(), android.provider.Settings.Secure.ANDROID_ID);
    return androidId;
 }

在Unity中獲取##

Unity獲取androidID首先需要獲取Unity環境中當前的activity，由activiy調用getContentResolver。

	private String GetAndroidID()
	{
		AndroidJavaClass up = new AndroidJavaClass ("com.unity3d.player.UnityPlayer");
		AndroidJavaObject currentActivity = up.GetStatic<AndroidJavaObject> ("currentActivity");
		AndroidJavaObject contentResolver = currentActivity.Call<AndroidJavaObject> ("getContentResolver");  
		AndroidJavaClass secure = new AndroidJavaClass ("android.provider.Settings$Secure");
		string android_id = secure.CallStatic<string> ("getString", contentResolver, "android_id");
		return android_id;
	}

在C中獲取

在C代碼中只能通過JNI方式調用java來獲取,代碼看起來比較亂，有很多同java進行交互的部分。獲取流程如下:

• 首先JVM加載native code所在動態庫的時候（loadlibrary）會自動調用JNI_OnLoad，這時候會初始化一個全局的JavaJVM，一個進程只能有一個JavaJVM。

• 當前線程獲取JNIEnv,調用AttachCurrentThread來獲得。

• 通過JNI獲取Java中的相關類，方法。獲取Context（getGlobalContext）的方法研究了很長時間，網上搜了好多資料。

• 得到jstring類型的Android,轉換成char *

• 最后返回。

#include <jni.h>
#include <assert.h>
#include "libavutil/avassert.h"

#define JNI_CLASS_PATH     /JNI/CLASS/path
static JavaVM* g_jvm=NULL;

static jobject getGlobalContext(JNIEnv *env)
{

    jclass activityThread = (*env)->FindClass(env,"android/app/ActivityThread");
    jmethodID currentActivityThread = (*env)->GetStaticMethodID(env,activityThread, "currentActivityThread", "()Landroid/app/ActivityThread;");
    jobject at = (*env)->CallStaticObjectMethod(env,activityThread, currentActivityThread);

    jmethodID getApplication = (*env)->GetMethodID(env,activityThread, "getApplication", "()Landroid/app/Application;");
    jobject context = (*env)->CallObjectMethod(env,at, getApplication);
    return context;
}

static jstring
_getAndroidID(JNIEnv *env, jobject thiz)
{
  
    jclass c_settings_secure = (*env)->FindClass(env, "android/provider/Settings$Secure");
    jclass c_context = (*env)->FindClass(env,"android/content/Context");
    if(c_settings_secure == NULL || c_context == NULL){
        return NULL;
    }
    //Get the getContentResolver method
    jmethodID m_get_content_resolver = (*env)->GetMethodID(env, c_context, "getContentResolver",
                                                           "()Landroid/content/ContentResolver;");
    if(m_get_content_resolver == NULL){
        return NULL;
    }
    //Get the Settings.Secure.ANDROID_ID constant
    jfieldID f_android_id = (*env)->GetStaticFieldID(env, c_settings_secure, "ANDROID_ID", "Ljava/lang/String;");

    if(f_android_id == NULL){
        return NULL;
    }
    jstring s_android_id = (*env)->GetStaticObjectField(env, c_settings_secure, f_android_id);
  
    //create a ContentResolver instance context.getContentResolver()
    jobject o_content_resolver = (*env)->CallObjectMethod(env, getGlobalContext(env), m_get_content_resolver);
    if(o_content_resolver == NULL || s_android_id == NULL){
        return NULL;
    }
    //get the method getString
    jmethodID m_get_string = (*env)->GetStaticMethodID(env, c_settings_secure, "getString",
                                                       "(Landroid/content/ContentResolver;Ljava/lang/String;)Ljava/lang/String;");

    if(m_get_string == NULL){
        return NULL;
    }
    //get the Android ID
    jstring android_id = (*env)->CallStaticObjectMethod(env, c_settings_secure,
                                                        m_get_string,
                                                        o_content_resolver,
                                                        s_android_id);
    return android_id;
}


static  char* jstringTostr( jstring jstr)
{    

    JNIEnv* env = NULL;
    if ((*g_jvm)->GetEnv(g_jvm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {

        return -1;
    }
    assert(env != NULL);    
    char* pStr = NULL;

    jclass     jstrObj   = (*env)->FindClass(env, "java/lang/String");
    jstring    encode    = (*env)->NewStringUTF(env, "utf-8");
    jmethodID  methodId  = (*env)->GetMethodID(env, jstrObj, "getBytes", "(Ljava/lang/String;)[B");
    jbyteArray byteArray = (jbyteArray)(*env)->CallObjectMethod(env, jstr, methodId, encode);
    jsize      strLen    = (*env)->GetArrayLength(env, byteArray);
    jbyte      *jBuf     = (*env)->GetByteArrayElements(env, byteArray, JNI_FALSE);

    if (jBuf > 0)
    {
        pStr = (char*)malloc(strLen + 1);
        if (!pStr)
        {
            return NULL;
        }
        memcpy(pStr, jBuf, strLen);
        pStr[strLen] = 0;
    }
   
    (*env)->ReleaseByteArrayElements(env, byteArray, jBuf, 0);
    //av_log(NULL, AV_LOG_INFO, "the android is end%s\n", pStr);
    return pStr;
}


char * getAndroidID()
{
    JNIEnv* env = NULL;
    if((*g_jvm)->AttachCurrentThread(g_jvm, &env, NULL) != JNI_OK)
    {
       return NULL;
    }
    jstring androidID = _getAndroidID(env,NULL);
    return jstringTostr(androidID);
}

JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved)
{
    JNIEnv* env = NULL;
    g_jvm = vm;
    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
       return -1;
    }
    assert(env != NULL);
    return JNI_VERSION_1_4;
}