Mr. CJ Technical Record: 2015

MainActivity.java

package com.example.test;

import android.app.Activity;

import android.os.Bundle;

import android.util.Log;

public class MainActivity extends Activity {

    //Load Jni library

    static {

  System.loadLibrary("JniLibrary");

}

    //Declare Jni method

    public native int callPknName(Context context);

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Log.i("Tag", "length of package name: " + callPknName(this));

}

}

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JniLibrary.c

#include <jni.h>

#include <stdlib.h>

#include <string.h>

#include <stdio.h>

JNIEXPORT jint JNICALL Java_com_example_test_pkg_callPknName (JNIEnv *env, jobject obj, jobject activity) {

 //Get java context class

 jclass java_class = (*env)->GetObjectClass(env, activity);

 //Check if get class

 if (java_class == 0) {

     return 0; // did not get class

}

 //Get method "java Context.getPackageName()"

 //"()Ljava/lang/String;" means this method has no input argument, and returns "String" type

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

 //Check if get method

 if (java_method == 0) {

     return 0;  //did not get method

}

 //Convert java string object to jstring

 jstring java_string = (*env)->CallObjectMethod(env, activity, java_method);

 //Check if get java string value

 if (java_string == 0) {

     return 0;  //did not get method

}

 //Conver jstring to char*

 const char *inputLic = (*env)->GetStringUTFChars(env, java_string, NULL);

     return strlen(inputLic);

}

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Reference:

6.1 Callback the Constructor to Create a New Java Object in the Native Code:

Stack Overflow:

Mr. CJ Technical Record