I'm trying to call a non static java method from C++ using the JNI on an Android project, but GetMethodID always return NULL.
this is my code:
void Java_com_kungfu_rabbit_KungFuRabbitActivity_nativeOnCreate(JNIEnv *env, jobject obj)
{
// this code works fine
jclass cls = env->FindClass("com/kungfu/rabbit/KungFuRabbitActivity");
jmethodID mid = env->GetStaticMethodID(cls, "foo", "()V");
env->CallStaticVoidMethod(cls, mid);
// this one fails:
jclass cls = env->GetObjectClass(obj);
jmethodID mid = env->GetMethodID(cls, "foo2", "()V");
env->CallVoidMethod(obj, mid);
}
I'm calling this native function from the class that extends Activity. foo is a public static void function, and foo2 is a public void function.
I can't understand why it fails...
Can anyone help me to understand?
Thanks in advance
Related
I have a layout design in Java that I am currently porting over to C++ via JNI. I am practically done at this point, but I am currently puzzled on how I am supposed to set up event handlers like setOnClickListener for example. I have gone through the JNI specification and have not gotten much luck.
If anyone can port the following snippet to C++ or lead me in the right direction (more reasonable due to how much code the result would be), that would be greatly appreciated.
public void setOnClickListener(boolean modification, int index, int commandIndex, final TextView textView){
final int key = index;
final int command = commandIndex;
if(modification) {
textView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
changingMenu(key, command, textView);
Runnable r = new Runnable() {
#Override
public void run() {
resetMenu(key, command, textView);
}
};
Handler h = new Handler();
h.postDelayed(r, 250);
}
});
return;
}
menuTitle.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
toggleMenu();
}
});
}
EDIT: Passing bad argument to setOnClickListener
Java
Object getProxy (MyInvocationHandler mih) {
ClassLoader classLoader = new ClassLoader() {
#Override
public Class<?> loadClass(String name) throws ClassNotFoundException {
return super.loadClass(name);
}
};
return java.lang.reflect.Proxy.newProxyInstance(classLoader, new Class[] { }, mih);
}
C++
jobject createProxyInstance(JNIEnv *env, jclass cls, CFunc cfunc) {
jclass cls_IH = env->FindClass("com/app/core/MyInvocationHandler");
jmethodID cst_IH = env->GetMethodID(cls_IH, "<init>", "(J)V");
jobject myIH = env->NewObject(cls_IH, cst_IH, (jlong)cfunc);
jclass klass = env->FindClass("com/app/core/Activity");
jmethodID method = env->GetMethodID(klass, "getProxy", "(Lcom/app/core/MyInvocationHandler;)Ljava/lang/Object;");
return env->CallObjectMethod(context, method, myIH); //Returning wrong object?
}
jobject aa (JNIEnv *env, jobject obj, jobject proxy, jobject method, jobjectArray args) {
__android_log_print(ANDROID_LOG_ERROR, "TEST", "SUCCESS");
}
void setListeners() {
jclass klass = env->FindClass("android/view/View");
jmethodID method = env->GetMethodID(klass, "setOnClickListener", "(Landroid/view/View$OnClickListener;)V");
klass = env->FindClass("android/view/View$OnClickListener");
env->CallVoidMethod(imageView, method, createProxyInstance(env, klass, &aa));
}
The syntax you show boils down to creating anonymous inner classes at compile time and inserting calls to create objects of these classes (with the correct variables in scope) in place of the new View.OnClickListener() { ... } expression.
I see the following two options:
For each different interface, you create a small Java class that implements the interface, with a native implementation of the interface's method(s). This is the most direct approach, but it does require you to keep the tens or hundreds of interface implementations straight.
You use java.lang.reflect.Proxy.newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) to dynamically create objects that implement the necessary interfaces. This will re-route each method invocation to your InvocationHandler implementation, which should be a Java class that has a native Object invoke(Object proxy, Method method, Object[] args) implementation.
To make all this reusable, you can implement this InvocationHandler to wrap a std::function object, so the final call to eg menuTitle.setOnClickListener might look like the following:
env->CallVoidMethod(menuTitle, menuTitle_setOnClickListener,
createProxyInstance(env, cls_View_OnClickListener, [](JNIEnv *env, jobject proxy, jobject method, jobjectArray args) {
...
});
For the latter solution, define the following Java class:
class MyInvocationHandler implements InvocationHandler {
private long cfunc;
MyInvocationHandler(long cfunc) { this.cfunc = cfunc; }
public native static Object invoke(Object proxy, Method method, Object[] args);
}
Which you implement on the C++ side as:
typedef jobject (*CFunc)(JNIEnv *env, jobject obj, jobject proxy, jobject method, jobjectArray args)
extern "C" jobject Java_MyInvocationHandler_invoke(JNIEnv *env, jobject obj, jobject proxy, jobject method, jobjectArray args) {
jclass cls_myIH = env->GetObjectClass(obj);
jfieldID fld_myIH_cfunc = env->GetFieldID(cls_myIH, "cfunc", "J");
CFunc cfunc = (CFunc)env->GetLongField(obj, fld_myIH_cfunc);
cfunc(env, proxy, method, args);
return nullptr;
}
Finally, we can implement createProxyInstance as follows:
jobject createProxyInstance(JNIEnv *env, jclass cls, CFunc cfunc) {
jclass cls_IH = env->GetClass("MyInvocationHandler");
jmethodID cst_IH = env->GetMethodID(cls_ID, "<init>", "(J)V");
jobject myIH = env->NewObject(cls_ID, cst_IH, (jlong)cfunc);
// now call Proxy.createProxyInstance with this object as InvocationHandler
}
I am trying to call a method in my java class from within a thread in the native code but not having any success. These are the global vars:
JavaVM* javaVM = NULL;
jclass activityClass;
jobject activityObj;
Code called on initialisation of the native code:
extern "C" {
JNIEXPORT jint JNICALL
naInit(JNIEnv *pEnv, jobject pObj, jstring pFileName, jstring, defaultStorageDirectory) {
pEnv->GetJavaVM(&javaVM);
jclass cls = pEnv->GetObjectClass(pObj);
activityClass = reinterpret_cast<jclass>((jclass) pEnv->NewGlobalRef(cls));
activityObj = pEnv->NewGlobalRef(pObj);
}
}
Code used within the thread function:
void *decodeAndRender(void * args) {
JNIEnv *env;
javaVM->AttachCurrentThread(&env, NULL);
jmethodID retryStartVideoMethodID = env->GetMethodID(activityClass, "retryStartVideo", "()V");
env->CallVoidMethod(activityObj, retryStartVideoMethodID);
javaVM->DetachCurrentThread();
return 0;
}
Java code :
public void retryStartVideo() {
Log.d(TAG, "METHOD CALLED FROM CPP ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
}
Error in logcat:
JNI DETECTED ERROR IN APPLICATION: JNI CallVoidMethodV called with pending exception java.lang.NoSuchMethodError: no non-static method "Ljava/lang/Class;.retryStartVideo()V"
I have set the instances of the calling class to be a global ref and used that when calling from within the thread function but it is still failing to find the method. I can use similar code to call a static method no problem but I need to be able to call a non static one.
I'm currently developping an android app with android studio, for this project i need to use a custom library written in c/c++ .
So i in order to do that i needed to use NDK.
The library contain methods that i need to implements in order to have access to specifics fonctions in android
My question is : how can I call my jni method inside the method existing in c
which will call a java method to store session key in the android system
So for a pratical exemple since it's maybe not clear:
In a file called lib_exemple.c i have three methods
the first one is the initialisation call to the library (jni to library c) -->working
JNIEXPORT void JNICALL
Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1init
(JNIEnv *env, jobject instance) {
lib_Example_init('0'); // c func of the library
}
then the second one is the jni who call a java method (jni to java) -> working
JNIEXPORT jint
JNICALL Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1store_1session_1key
(JNIEnv * env, jobject jobject1, jbyte jbyte1, jchar jchar1, jbyte jbyte2){
jclass clazz = (*env)->FindClass(env, "com/example/libExemple/Libs/ExempleLib");
jmethodID mCurrentActivityId = (*env)->GetMethodID(env, clazz, "KeyStoreSessionKey", "(BCB)I");
jint result = (*env)->CallIntMethod(env, jobject1, mCurrentActivityId, jbyte1, jchar1, jbyte2);
return result;
}
and the third method is the one the library c have in it (library C to jni)
int lib_Exemple_store_session_key(uint8_t Session, P_KEY_ST_T pKey, uint8_t keyType) {
//i want to call jni func here , so the librairy can access the native android function
return 0;
}
then to configure the ndk in a file called ExempleLib.java i have defined
static {
System.loadLibrary("LibExemple");
}
then the prototype of the initialisation of the library
public native void libExemple_init();
the prototype of the first method in lib_exemple.c
public native int lib_Exemple_store_session_key(byte pKey, char key_length, byte keyIndex);
and the java fonction called by it
protected int KeyStoreSessionKey(byte pKey, char key_length, byte keyIndex) {
...
}
my mainActivity contain
ExempleLib LibFunc = new ExempleLib();
Log.d(TAG, "init lib" );
LibFunc.lib_Exemple_init();
My goal is that after initialising my library and call an init function , it can call the first method in the second method of lib_exemple.c (the one used in the library )
thanks
EDIT :
The solution of my problem is when i initialize the lib , i need to save jvm
so i can access the JNIenv in the library method directly
jobject Savedinstance = NULL;
static JavaVM *cachedJVM;
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *jvm, void *reserved) {
cachedJVM = jvm;
return JNI_VERSION_1_6;
}
JNIEnv *AttachJava() {
JavaVMAttachArgs args = {JNI_VERSION_1_6, 0, 0};
JNIEnv *java;
(*cachedJVM)->AttachCurrentThread(cachedJVM, &java, &args);
return java;
}
JNIEXPORT jint JNICALL
Java_com_example_vgosselin_libExemple_Libs_ExempleLib_lib_1init(JNIEnv *env,
jobject instance) {
Savedinstance = instance;
void *element = 0;
jint result;
result = lib_Exemple_init_();
return result;
}
so i can call the java method in
int lib_Exemple_store_session_key(uint8_t Session, P_KEY_ST_T pKey, uint8_t keyType) {
JNIEnv *NewEnv = AttachJava();
jclass clazz = (*NewEnv)->FindClass(NewEnv,"com/example/vgosselin/libExemple/Libs/ExempleLib");
jmethodID mCurrentActivityId = (*NewEnv)->GetMethodID(NewEnv,clazz,"KeystoreStoreKey","([BCB)I");
jint result;
jbyteArray Data = 0;
jchar Key = 0;
jbyte Type = 0;
result = (*NewEnv)->CallIntMethod(NewEnv, Savedinstance, mCurrentActivityId, Data, Key, Type);
return result;
}
and now i don't need the method in jni syntax anymore
JNIEXPORT jint JNICALL Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1store_1session_1key
I a Library in C that I'm leveraging for an Android application. This library has an audio stream that it occasionally flushes. When this happens it calls a write callback function of my design.
My intent is to have that C callback call a method on a specific Java Object which will handle stuff with the strem.
Currently I have code like so:
methodID compressionHandler=0;
jobject compressionHandlerClass;
int audioBufferChunkSize;
static JavaVM *gJavaVM;
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
gJavaVM = vm;
return JNI_VERSION_1_6;
}
JNIEXPORT void JNICALL
Java_com_my_code_init(JNIEnv* env, jobject obj, /*classpath of the class we want to call against*/jstring compressedAudioHandlerPath, /*class instance we want to call against*/jobject callbackClass) {
......
// this is a global ref as per:
//http://stackoverflow.com/questions/14765776/jni-error-app-bug-accessed-stale-local-reference-0xbc00021-index-8-in-a-tabl
compressionHandlerClass = (*env)->NewGlobalRef(env,callbackClass);
// name of the class
const char *classLocation;
// convert jString to c String
classLocation = (*env)->GetStringUTFChars( env, compressedAudioHandlerPath , NULL ) ;
// tmp variable for holding the class location, relates to the above issue with garbage collection
jclass clazz = (*env)->FindClass(env, classLocation);
// the actual method that we want to call, this gets used in the writeCallback
compressionHandler = (*env)->GetMethodID(env, clazz, "handleCompressedAudio", "([B)V");
......
}
The callback method looks like so:
void writeCallback(const FLAC__StreamEncoder *encoder, const FLAC__byte buffer[], size_t bytes, unsigned samples, unsigned current_frame, void *client_data) {
JNIEnv *env;
int isAttached = 0;
if ((status = (*gJavaVM)->GetEnv(gJavaVM, (void**)&env, JNI_VERSION_1_6)) < 0) {
if ((status = (*gJavaVM)->AttachCurrentThread(gJavaVM, &env, NULL)) < 0) {
return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
}
isAttached = 1;
}
if(*env!=0 && compressionHandler!=0){
jbyteArray arr = (*env)->NewByteArray(env,bytes);
(*env)->SetByteArrayRegion(env,arr, 0, bytes, (jbyte*)buffer);
(*env)->CallVoidMethod(env,compressionHandlerClass, compressionHandler,arr);
free(arr);
free(env);
free(isAttached);
}
}
I'm getting crashes at the CallVoidMethod, that signature of which is an interface implemented by whatever object I pass in:
public interface CompressedAudioHandler {
void handleCompressedAudio(byte[] buff);
}
I suspect that I am improperly attaining/keep references to these objects, but I haven't found a great way to handle that. Any advice on how I can more correctly handle this?
I am having a problem with JNI, calling a method from C++ to Java.
I am trying to call a void method that takes a boolean. My java code is the following:
public void setStatus(boolean bool) {
// Do stuff...
}
public native void initialize(int defaultPort);
In my C++ code, I am making a struct to hold the env and object and pass it to a thread:
JNIEXPORT void JNICALL Java_com_device_client_HostConnection_initialize
(JNIEnv * env, jobject obj, jint port)
{
struct javaInfo* data = (struct javaInfo*) malloc(sizeof(struct javaInfo));
data->env = env;
data->javaObjHost = obj;
pthread_t pth;
pthread_create(&pth, NULL, startServer, (void *) data);
free(data);
}
In the actual function, I am trying to obtain the class and then the MethodID and then call the void method, as follows:
void *startServer(void* arg) {
struct javaInfo* data = (struct javaInfo*) arg;
JNIEnv* env = data->env;
jobject javaObjHost = data->javaObjHost;
cls = env->GetObjectClass(javaObjHost);
mid = env->GetMethodID(cls, "setStatus", "(Z)V");
if (mid == 0) {
exit(-1);
}
env->CallVoidMethod(javaObjHost, mid, true);
}
It is hard for me to debug with JNI. I have tried putting a breakpoint in Eclipse in setStatus() but it never gets called. exit() is not called as well. The programs stomps for a second or two, then continues. I am not sure what is going on.
Could anyone please help me?
Thank you very much.
You cannot pass env pointers to other threads. You need to join the thread to the JVM.
In the original thread, called GetJavaVM to obtain a JavaVM pointer:
JavaVM *vm = 0;
env->GetJavaVM(&vm);
Then in the other thread, attach the VM to that thread and get a new env pointer:
vm->AttachCurrentThread(&env, 0);