get application name from NDK

Question

I need to get name of my android application from the native side somethin like that:

 android.content.context context=(android.content.context) this;//current activiy
 Resources appR =context.getResources();
 String packageName=context.getPackageName();
 int id=appR.getIdentifier("app_name","string",packageName );
 CharSequence txt = appR.getText(id);

my native code like that:

  jstring Java_com_AnalyticToolC_AnalyticToolActivity_JNISendData(JNIEnv* env,jobject entryObject,jobject contxt)
 {

   char *realAppName;
 realAppName=(char *)malloc(16 * 1024);
 jclass android_content_Context =(*env)->GetObjectClass(env, contxt);
    jmethodID midGetPackageName = (*env)->GetMethodID(env, android_content_Context, "getPackageName", "()Ljava/lang/String");
 jstring packageName=(*env)->CallObjectMethod(env, contxt, midGetPackageName);
jmethodID midGetResources = (*env)->GetMethodID(env, android_content_Context, "getResources", "()L");
    jobject jResource=(*env)->CallObjectMethod(env, context, midGetResources);

   jclass resource_Class=(*env)->GetObjectClass(env, jResource);
   jmethodID midGetIdentifier = (*env)->GetMethodID(env, resource_Class, "getIdentifier", "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String)I");
   jstring app_name=(*env)->NewStringUTF(env,"app_name");
   jstring TypeName=(*env)->NewStringUTF(env,"string");
   int id=(*env)->CallObjectMethod(env, jResource, midGetIdentifier,app_name,TypeName,packageName);

  jmethodID midGetAppName = (*env)->GetMethodID(env, resource_Class,"getText","(I)Ljava/lang/String");
  jstring appName=(*env)->CallObjectMethod(env, jResource, midGetAppName,id);   

  realAppName=(*env)->GetStringUTFChars(env, appName, NULL);
}

and i just pass the activity to my native methon from java code.

and i don't have a chance to write this code in java class then call it form my NDK application I'm trying a lot to pass a context object as jobject to my native code but it always crash. dose any one have any idea?

Answer 1

Reflected Java access in C is ugly, ugly, ugly, just like you've demonstrated. Pass the app name as an extra string parameter.

EDIT: OK, you want reflection, reflection you'll get.

Your native method belongs to class AnalyticToolActivity. As a nonstatic class method, it has a this pointer on every call. Unlike C++ and Java methods, this pointer is passed explicitly as the second parameter. The method has two mandatory parameters - a JNIEnv * and a jobject. The second one corresponds to the this pointer of the Java object.

So if your AnalyticToolActivity is a subclass of Activity - quite likely - the entryObject parameter is an instance of Activity, meaning it's an instance of Context. So get rid of the third parameter (contxt), and your JNI code can go like this:

jclass android_content_Context =(*env)->GetObjectClass(env, entryObject);
//or use FindClass

jmethodID midGetPackageName = (*env)->GetMethodID(env,
    android_content_Context,
    "getPackageName",
    "()Ljava/lang/String;");

jstring packageName=(*env)->CallObjectMethod(env, entryObject, midGetPackageName); 

and so forth.