使用JNI从本机线程调用Java方法时遇到问题(C++)

Question

我有一个JNI问题,我希望有人可以帮助我.
我正在尝试从本机线程调用名为LUSOutputJNI的Java类的构造函数.
它一直在这个特定类的FindClass(...)上失败.

这是代码:

 LOGE("1");
    JNIEnv *env = NULL;

    LOGE("2");
    int res = -1;
    res = g_vm->AttachCurrentThread(&env, NULL);

    if(env == NULL)
    {
        LOGE("env is NULL, AttachCurrentThread failed");;
    }


    if(res >= 0)
        LOGE("AttachCurrentThread was successful");
    jclass clazz = NULL;
    jmethodID cid;

    jclass clazzESEngine;
    jmethodID callbackid;

    jobject jCoreOut;
    static jfieldID fid_ActionState = NULL;
    static jfieldID fid_nSpeed = NULL;
    static jfieldID fid_nType = NULL;
    static jfieldID fid_nInProcess = NULL;
    static jfieldID fid_nX = NULL;
    static jfieldID fid_nY = NULL;
    LOGE("3");

    static const char* const ECOClassName = "lus/android/sdk/LUSOutputJNI";
    //static const char* const ECOClassName = "android/widget/TextView";
    clazz = env->FindClass(ECOClassName);
    if (clazz == NULL) {
        LOGE("Can't find class LUSOutputJNI");

    }
    else
        LOGE("lus/android/sdk/LUSOutputJNI was found, YEY!!");

    LOGE("4");
    cid = env->GetMethodID(clazz,"<init>", "()V");
    LOGE("5");
    jCoreOut = env->NewObject(clazz, cid);

    LOGE("6");    

这是失败时的logcat输出:

E/lusCore_JNI( 3040): 1
E/lusCore_JNI( 3040): 2
E/lusCore_JNI( 3040): AttachCurrentThread was successful
E/lusCore_JNI( 3040): 3
E/lusCore_JNI( 3040): Can't find class LUSOutputJNI
E/lusCore_JNI( 3040): 4
W/dalvikvm( 3040): JNI WARNING: JNI method called with exception raised  

观察:

• 我从AttachCurrentThread得到一个0的结果,这意味着这个附件成功+ env指针不再是NULL.
• 我确定LUSOutputJNI的包名声明(三重检查......)
• 当我尝试使用更流行的类名(如android/widget/TextView)运行FindClass(..)时,我获得了积极的匹配.它就在那里.意味着线程附件和env变量都可以.(我能假设吗？)
• 当我尝试从运行它的JNI线程的JNI方法运行以下代码时,它会发现LUSOutputJNI类没有问题.

我究竟做错了什么？

帮助将不胜感激:)

谢谢你的时间,

伊达

Answer 1

找到答案\在这里工作.(寻找常见问题解答:"FindClass在JNI提示中找不到我的课程" )

我基本上保存了一个全局引用到所需的jclass对象.
然而,为了编译代码,却必须克服C/JNI和C++/JNI之间的一些邪恶的JNI变化.
这就是我如何编译和工作NewGlobalRef.

jclass localRefCls = env->FindClass(strLUSClassName);
if (localRefCls == NULL) {
    LOGE("Can't find class %s",strLUSCoreClassName);
    return result;
}

//cache the EyeSightCore ref as global
 /* Create a global reference */
 clazzLUSCore = (_jclass*)env->NewGlobalRef(localRefCls);

 /* The local reference is no longer useful */
 env->DeleteLocalRef(localRefCls);

 /* Is the global reference created successfully? */
 if (clazzLUSCore == NULL) {
     LOGE("Error - clazzLUSCore is still null when it is suppose to be global");
     return result; /* out of memory exception thrown */
 }  

我希望这可以帮助任何人.