Showing Dialog

 @FXML
    public void showDialogPane() {
        // using Dialog methods
        Dialog<ButtonType> dialog = new Dialog<>();

        // we must set owner which invokes the dialog
        dialog.initOwner(mainBorderPane.getScene().getWindow());

        // setting a header title to dialog pane
        dialog.setHeaderText("Enter your new To Do schedule");

        // setting a window title to dialog
        dialog.setTitle("Add new item");

        // we need to instantiate the FXMLLoader to use it
        FXMLLoader fxmlLoader = new FXMLLoader();

        // setting the FXML file location which will be loaded later
        fxmlLoader.setLocation(getClass().getResource("additemdialog.fxml"));

        try {
            // trying to load the content from FXML file into the dialog pane
            dialog.getDialogPane().setContent(fxmlLoader.load());
        } catch (IOException e ) {
            e.getStackTrace();
            return;
        }

        // creating OK and Cancel button to dialog window
        dialog.getDialogPane().getButtonTypes().add(ButtonType.OK);
        dialog.getDialogPane().getButtonTypes().add(ButtonType.CANCEL);

        // showing the dialog window and waiting for response by the buttons created above
        Optional<ButtonType> result = dialog.showAndWait();

        if ( result.isPresent() && result.get() == ButtonType.OK) {
            // check for pressing an OK button

            // we must get DialogController instance
            DialogController controller = fxmlLoader.getController();

            // getting the newest ToDo item added in the list
            TodoItem item = controller.processResult();

            // auto-selecting the newest todo item
            todoListView.getSelectionModel().select(item);
        }
        else {
            System.out.println("Cancel is pressed!");
        }
    }