A way to get PackageInfo when app start

 package com.splash5.spa;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

import android.app.Application;
import android.content.pm.PackageInfo;
import android.util.Log;

public class MyApplication extends Application
{
    private static PackageInfo getPackageInfo() throws Exception
    {
        PackageInfo pi = null;

        final Class<?> activity_thread_class = Class.forName("android.app.ActivityThread");
        final Class<?> package_manager_interface = Class.forName("android.content.pm.IPackageManager");
        final Class<?> android_version_class = Class.forName("android.os.Build$VERSION");

        final Method current_package_name_method = activity_thread_class.getMethod("currentPackageName");
        final Method get_package_manager_method = activity_thread_class.getMethod("getPackageManager");
        final Field sdk_int_field = android_version_class.getField("SDK_INT");

        final Object package_manager = get_package_manager_method.invoke(activity_thread_class);
        final Object packageName = current_package_name_method.invoke(activity_thread_class);
        final int sdk_int = sdk_int_field.getInt(android_version_class);

        if (sdk_int < 16)
        {
            final Method get_package_info = package_manager_interface.getMethod("getPackageInfo", new Class<?>[]{String.class, int.class});
            pi = (PackageInfo)get_package_info.invoke(package_manager, packageName, 0);
        }
        else
        {
            // 4.1 : android.os.UserId, 4.2+ : android.os.UserHandle
            final Class<?> user_handle_class = Class.forName((sdk_int < 17 ? "android.os.UserId" : "android.os.UserHandle"));

            final Method get_package_info = package_manager_interface.getMethod("getPackageInfo", new Class<?>[]{String.class, int.class, int.class});
            final Method my_user_id = user_handle_class.getMethod("myUserId");
            final Object userId = my_user_id.invoke(user_handle_class);

            pi = (PackageInfo)get_package_info.invoke(package_manager, packageName, 0, userId);
        }

        return pi;
    }

    static
    {
        try
        {
            final PackageInfo pi = getPackageInfo();

            Log.d("Reward", "package name = " + pi.packageName);
            Log.d("Reward", "version name = " + pi.versionName);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}