Read Version number from Gradle build file

MainActivity.java

    /**
     * Called when an item in the navigation menu is selected.
     *
     * @param item The selected item
     * @return true to display the item as the selected item
     */
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {

        int id = item.getItemId();
        switch (id) {

          case R.id.nav_version: // App Version      
            String version = "";
            try {
              PackageInfo pInfo = this.getPackageManager().getPackageInfo(getPackageName(), 0);
              version = "version: " + pInfo.versionName;              
            } catch (PackageManager.NameNotFoundException e) {           
              e.printStackTrace();            
            }
            
            AlertDialog.Builder versionDialogBuilder = new AlertDialog.Builder(this);            
            versionDialogBuilder.setTitle(getString(R.string.app_name));            
            versionDialogBuilder.setMessage(version);            
            versionDialogBuilder.setNeutralButton("OK", new DialogInterface.OnClickListener() {            
              public void onClick(DialogInterface dialog, int which) {              
                //do nothing                
              }
              
            });

            AlertDialog versionDialog = versionDialogBuilder.create();            
            versionDialog.show();            
            break;

            
          case R.id.nav_logout: // Logout            
            
            /* Get confirmation from user before logout*/            
            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);            
            alertDialogBuilder.setTitle(getString(R.string.sign_out));
            
            alertDialogBuilder.setMessage("Are you sure you want to logout?");            
            alertDialogBuilder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            
              public void onClick(DialogInterface dialog, int which) {              
                //do nothing                
              }           
            });
            
            alertDialogBuilder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {            
              @Override              
              public void onClick(DialogInterface dialog, int which) {                               
                if (which == AlertDialog.BUTTON_POSITIVE) {                
                  /* Remove the saved email ID and password*/                  
                  SharedPreferences sp = getSharedPreferences(Utils.SP_FILE, Context.MODE_PRIVATE);                  
                  SharedPreferences.Editor Ed = sp.edit();                  
                  Ed.putString("Email", "");                  
                  Ed.putString("Passwd", "");
                  Ed.apply();
                  /* Relaunch the Welcome Activity and ask user to Login */
                  startActivity(new Intent(MainActivity.this, WelcomeActivity.class)); 
                } 
              }
            });
            AlertDialog alertDialog = alertDialogBuilder.create();
            alertDialog.show();
            break;
        }
      DrawerLayout drawer = findViewById(R.id.drawer_layout_main);
      drawer.closeDrawer(GravityCompat.START);
      return true;
    }