Android popup popup by oncreate

You are trying to show the popup even before the activity window is displayed. With the post method, we can wait for all the required lifecycle methods to complete.

Try the following:

private void loadingPopup() {
    LayoutInflater inflater = this.getLayoutInflater();
    final View layout = inflater.inflate(R.layout.loading_dialog, null);

    final PopupWindow windows = new PopupWindow(layout , 300,300,true);
    windows.setFocusable(false);
    windows.setTouchable(true); 
    windows.setOutsideTouchable(true);
    layout.post(new Runnable() {
        public void run() {
            windows.showAtLocation(layout,Gravity.CENTER, 0, 0);
        }
    });
}