/** Show the about popup */
 private void showPopup() {
   if (mPopupWindow == null) {
     LayoutInflater inflater =
         (LayoutInflater) MainActivity.this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
     mPopupLayout =
         inflater.inflate(R.layout.about_popup, (ViewGroup) findViewById(R.id.popup_element));
     mPopupLayout.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
     mPopupWindow = new DragablePopupWindow(mPopupLayout);
     int height = mPopupLayout.getMeasuredHeight();
     int width = mPopupLayout.getMeasuredWidth();
     mPopupWindow.setWidth(width);
     mPopupWindow.setHeight(height);
     TextView websiteLink = (TextView) mPopupLayout.findViewById(R.id.about_website);
     websiteLink.setOnClickListener(
         new View.OnClickListener() {
           public void onClick(View v) {
             // open the link on the default browser
             String url = "http://www.robbertvdzon.com";
             Intent i = new Intent(Intent.ACTION_VIEW);
             i.setData(Uri.parse(url));
             startActivity(i);
           }
         });
   }
   mPopupWindow.showAtLocation(mPopupLayout, Gravity.CENTER, 0, 0);
   mPopupWindow.moveToLastPosition(); // in case popup was moved before
 }