Question

I’m currently using SWIG/jni to call C++ functions from java for an Android app. However, I’m having difficulty whenever the function returns a jstring. I get the following errors in LogCat upon application launch…

ERROR: Unable to find decl for native Lcom/example/swigJNI;.plugin_name:L()java/lang/String

ERROR: Unable to find decl for native Lcom/example/swigJNI;.plugin_description:L()java/lang/String

Here is some code that might be useful to examine…

SWIG generated wrapper code:

 SWIGEXPORT jstring JNICALL Java_swigJNI_1plugin_1name(JNIEnv *jenv, jclass jcls) {
  jstring jresult = 0 ;
  char *result = 0 ;

  (void)jenv;
  (void)jcls;
  result = (char *)plugin_name();
  if (result) jresult = jenv->NewStringUTF((const char *)result);
  return jresult;
}


SWIGEXPORT jstring JNICALL Java_swigJNI_1plugin_1description(JNIEnv *jenv, jclass     jcls) {
  jstring jresult = 0 ;
  char *result = 0 ;

  (void)jenv;
  (void)jcls;
  result = (char *)plugin_description();
  if (result) jresult = jenv->NewStringUTF((const char *)result);
  return jresult;
}

Declaration of JNI Native methods:

static const JNINativeMethod methods[] = {
    {"plugin_name", "()Ljava/lang/String", (void*) Java_swigJNI_1plugin_1name},
    {"plugin_description", "()Ljava/lang/String", (void*) Java_swigJNI_1plugin_1description}
};

I’ve been successful in executing JNI_onLoad() and RegisterNatives() when the functions return int’s, however strings have been quite problematic for me. I don’t quite understand how these functions aren’t being found. Is there something that I’m missing?

Answer 1

Ahh, I feel like a fool!

The signature I was using for string was…

()Ljava/lang/String

when it should really be…

()Ljava/lang/String;

Forgot the semi-colon. Ack!