Solution posted by Denys S. in the question post:
I quite messed it up with c to c++ conversion (basically env variable stuff), but I got it working with the following code for C++:
#include <string.h>
#include <stdio.h>
#include <jni.h>
jstring Java_the_package_MainActivity_getJniString( JNIEnv* env, jobject obj){
jstring jstr = (*env)->NewStringUTF(env, "This comes from jni.");
jclass clazz = (*env)->FindClass(env, "com/inceptix/android/t3d/MainActivity");
jmethodID messageMe = (*env)->GetMethodID(env, clazz, "messageMe", "(Ljava/lang/String;)Ljava/lang/String;");
jobject result = (*env)->CallObjectMethod(env, obj, messageMe, jstr);
const char* str = (*env)->GetStringUTFChars(env,(jstring) result, NULL); // should be released but what a heck, it's a tutorial :)
printf("%s\n", str);
return (*env)->NewStringUTF(env, str);
}
And next code for java methods:
public class MainActivity extends Activity {
private static String LIB_NAME = "thelib";
static {
System.loadLibrary(LIB_NAME);
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView tv = (TextView) findViewById(R.id.textview);
tv.setText(this.getJniString());
}
// please, let me live even though I used this dark programming technique
public String messageMe(String text) {
System.out.println(text);
return text;
}
public native String getJniString();
}