android - AndroidRuntime::getJNIEnv() returns NULL -

i have below code snippet in jni part:

jnienv* env = androidruntime::getjnienv(); 

the above statement returns null in function. use env , call method in java code using callback mechanism.

it's part of code in getjnienv() returns null.

if (vm->getenv((void**) &env, jni_version_1_4) != jni_ok) {         return null; } 

can please tell me what's wrong code? looks pretty normal me since other functions in jni have similar implementation.

first, don't use androidruntime::getjnienv(). that's not part of ndk api. should using jni getenv function instead.

second, getenv returns null if current thread not attached vm. (remember, jnienv thread-specific.) if created thread yourself, need use jni attachcurrentthread function attach it.

both of these require javavm pointer. there's 1 of these per process, can during jni_onload or setup call program (getjavavm function) when have jnienv passed in.

if haven't yet, read through jni tips page (which includes references comprehensive jni docs).