How can I bypass the JavaFX's TableView "placeholder"?


Question

JavaFX's TableView has a placeholder property that is basically a Node that gets displayed in the TableView whenever it is empty. If this property is set to null (its default value), it appears as a Label or some other text based Node that says "There is no content in the table."

But if there are any rows of data in the table, then the placeholder Node disappears and the entire vertical space in the TableView gets filled with rows, including empty rows if there isn't enough data to fill the whole table.

These empty rows are what I want, even when the table is empty. In other words, I don't want to use the placeholder at all. Does anyone know how I can do this?

I'd rather not do something kludgey like put a empty-looking row in the TableView whenever it's supposed to be actually empty.

1
9
6/7/2013 8:43:42 PM

Unfortunately, the old issue is still not fixed in fx9 nor fx10. So revisited the hacks in the context of fx9. There had been changes, good and bad ones:

  • Skins moved into a public package which now allows to subclass them without accessing hidden classes (good)
  • the move introduced a bug which doesn't allow to install a custom VirtualFlow (fixed in fx10)
  • reflective access to hidden members will be strongly disallowed (read: not possible) sometime in future

While digging, I noticed ever so slight glitches with the hacks (note: I did not run them against fx8, so these might be due differences in fx8 vs fx9!)

  • the forced in-/visibility of placeholder/flow worked fine except when starting up with an empty table (placeholder was shown) and enlarging the table while empty (the "new" region looks empty)
  • faking the itemCount to not-empty lets the rows dissappear on pressing navigation keys (which probably is not a big problem because users tend to not navigate an empty table) - this is definitely introduced in fx9, working fine in fx8

So I decided to go with the visibility enforcement: the reason for the slight glitches is that layoutChildren doesn't layout the flow if it thinks the placeholder is visible. That's handled by including the flow in the layout if super didn't.

The custom skin:

/**
 * TableViewSkin that doesn't show the placeholder.
 * The basic trick is keep the placeholder/flow in-/visible at all 
 * times (similar to https://stackoverflow.com/a/27543830/203657).
 * <p> 
 * 
 * Updated for fx9 plus ensure to update the layout of the flow as
 * needed.
 * 
 * @author Jeanette Winzenburg, Berlin
 */
public class NoPlaceHolderTableViewSkin<T> extends TableViewSkin<T>{

    private VirtualFlow<?> flowAlias;
    private TableHeaderRow headerAlias;
    private Parent placeholderRegionAlias;
    private ChangeListener<Boolean> visibleListener = (src, ov, nv) -> visibleChanged(nv);
    private ListChangeListener<Node> childrenListener = c -> childrenChanged(c);

    /**
     * Instantiates the skin.
     * @param table the table to skin.
     */
    public NoPlaceHolderTableViewSkin(TableView<T> table) {
        super(table);
        flowAlias = (VirtualFlow<?>) table.lookup(".virtual-flow");
        headerAlias = (TableHeaderRow) table.lookup(".column-header-background");

        // startet with a not-empty list, placeholder not yet instantiatet
        // so add alistener to the children until it will be added
        if (!installPlaceholderRegion(getChildren())) {
            installChildrenListener();
        }
    }


    /**
     * Searches the given list for a Parent with style class "placeholder" and
     * wires its visibility handling if found.
     * @param addedSubList
     * @return true if placeholder found and installed, false otherwise.
     */
    protected boolean installPlaceholderRegion(
            List<? extends Node> addedSubList) {
        if (placeholderRegionAlias !=  null) 
            throw new IllegalStateException("placeholder must not be installed more than once");
        List<Node> parents = addedSubList.stream()
                .filter(e -> e.getStyleClass().contains("placeholder"))
                .collect(Collectors.toList());
        if (!parents.isEmpty()) {
            placeholderRegionAlias = (Parent) parents.get(0);
            placeholderRegionAlias.visibleProperty().addListener(visibleListener);
            visibleChanged(true);
            return true;
        }
        return false;
    }


    protected void visibleChanged(Boolean nv) {
        if (nv) {
            flowAlias.setVisible(true);
            placeholderRegionAlias.setVisible(false);
        }
    }


    /**
     * Layout of flow unconditionally.
     * 
     */
    protected void layoutFlow(double x, double y, double width,
            double height) {
        // super didn't layout the flow if empty- do it now
        final double baselineOffset = getSkinnable().getLayoutBounds().getHeight() / 2;
        double headerHeight = headerAlias.getHeight();
        y += headerHeight;
        double flowHeight = Math.floor(height - headerHeight);
        layoutInArea(flowAlias, x, y,
                width, flowHeight,
                baselineOffset, HPos.CENTER, VPos.CENTER);
    }


    /**
     * Returns a boolean indicating whether the flow should be layout.
     * This implementation returns true if table is empty.
     * @return
     */
    protected boolean shouldLayoutFlow() {
        return getItemCount() == 0;
    }


    /**
     * {@inheritDoc} <p>
     * 
     * Overridden to layout the flow always.
     */
    @Override
    protected void layoutChildren(double x, double y, double width,
            double height) {
        super.layoutChildren(x, y, width, height);
        if (shouldLayoutFlow()) {
            layoutFlow(x, y, width, height);

        }
    }

    /**
     * Listener callback from children modifications.
     * Meant to find the placeholder when it is added.
     * This implementation passes all added sublists to 
     * hasPlaceHolderRegion for search and install the 
     * placeholder. Removes itself as listener if installed.
     * 
     * @param c the change 
     */
    protected void childrenChanged(Change<? extends Node> c) {
        while (c.next()) {
            if (c.wasAdded()) {
                if (installPlaceholderRegion(c.getAddedSubList())) {
                    uninstallChildrenListener();
                    return;
                }

            }
        }
    }


    /**
     * Installs a ListChangeListener on the children which calls
     * childrenChanged on receiving change notification. 
     * 
     */
    protected void installChildrenListener() {
        getChildren().addListener(childrenListener);
    }

    /**
     * Uninstalls a ListChangeListener on the children:
     */
    protected void uninstallChildrenListener() {
        getChildren().removeListener(childrenListener);
    }


}

Usage example:

public class EmptyPlaceholdersInSkin extends Application {

    private Parent createContent() {
        // initially populated
        //TableView<Person> table = new TableView<>(Person.persons()) {
        // initially empty
        TableView<Person> table = new TableView<>() {

            @Override
            protected Skin<?> createDefaultSkin() {
                return new NoPlaceHolderTableViewSkin<>(this);
            }

        };
        TableColumn<Person, String> first = new TableColumn<>("First Name");
        first.setCellValueFactory(new PropertyValueFactory<>("firstName"));

        table.getColumns().addAll(first);

        Button clear = new Button("clear");
        clear.setOnAction(e -> table.getItems().clear());
        clear.disableProperty().bind(Bindings.isEmpty(table.getItems()));
        Button fill = new Button("populate");
        fill.setOnAction(e -> table.getItems().setAll(Person.persons()));
        fill.disableProperty().bind(Bindings.isNotEmpty(table.getItems()));
        BorderPane pane = new BorderPane(table);
        pane.setBottom(new HBox(10, clear, fill));
        return pane;
    }


    @Override
    public void start(Stage stage) throws Exception {
        stage.setScene(new Scene(createContent()));
        stage.show();
    }

    public static void main(String[] args) {
        Application.launch(args);
    }

    @SuppressWarnings("unused")
    private static final Logger LOG = Logger
            .getLogger(EmptyPlaceholdersInSkin.class.getName());

}
2
1/26/2018 1:26:46 PM

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