JavaFX 的 TableView 有一个 placeholder属性基本上是一个 Node，只要它为空，它就会显示在 TableView 中。如果此属性设置为 null(其默认值)，它将显示为 Label 或其他一些基于文本的 Node，表示“表中没有内容”。

但是如果表格中有任何数据行，那么占位符 Node 就会消失并且 TableView 中的整个垂直空间会被行填充，包括空行如果没有足够的数据来填满整个表格。

这些空行是我想要的，即使表格是空的。换句话说，我根本不想使用占位符。有谁知道我该怎么做？

我宁愿不做一些笨拙的事情，比如在 TableView 中放一个看起来空的行，但实际上它应该是空的。

最佳答案

不幸的是，old issue在 fx9 和更高版本(包括 fx18)中仍未修复。

fx9 的原始皮肤修改(见水平线下方)似乎仍适用于 fx18。尽管可以稍微改进，因为 fx12 引入了对流和 tableHeaderRow 的访问。

在尝试将其调整为更新的 api 时，我想出了一个 - 同样肮脏 且未经测试的 - 方法。这个想法是覆盖实际的布局方法，即在布置表格的各个子项时调用的方法，注意占位符并将其替换为流程:

public class NoPlaceHolderSkin<T> extends TableViewSkin<T> {

    public NoPlaceHolderSkin(TableView<T> control) {
        super(control);
    }

    @Override
    protected void layoutInArea(Node child, double areaX, double areaY, double areaWidth,
            double areaHeight, double areaBaselineOffset, HPos halignment, VPos valignment) {
        if (child.getStyleClass().contains("placeholder")) {
            child.setVisible(false);
            child = getVirtualFlow();
            child.setVisible(true);
        }
        super.layoutInArea(child, areaX, areaY, areaWidth, areaHeight, areaBaselineOffset, halignment, valignment);
    }
}

因此在 fx9 的上下文中重新审视了黑客。有好有坏的变化:

• 皮肤已移至公共(public)包中，现在允许在不访问隐藏类的情况下对其进行子类化(好)
• 移动introduced a bug不允许安装自定义 VirtualFlow(已在 fx10 中修复)
• 将来某个时候将强烈禁止对隐藏成员的反射访问(阅读:不可能)

在挖掘过程中，我注意到这些 hack 有非常轻微的故障(注意:我没有针对 fx8 运行它们，所以这些可能是 fx8 与 fx9 的差异造成的!)

• 占位符/流的强制可见性工作正常，除非从空表开始(显示占位符)并在空表时放大表("new"区域看起来是空的)
• 将 itemCount 伪造为非空让行在按下导航键时消失(这可能不是一个大问题，因为用户往往不会导航空表)——这在 fx9 中肯定引入，在 fx8 中工作正常

所以我决定继续执行可见性:出现轻微故障的原因是 layoutChildren 在认为占位符可见时不会对流进行布局。如果 super 没有，则通过在布局中包含流来处理。

自定义皮肤:

/**
 * 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);
    }
    
    
}

使用示例:

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());

}

关于java - 如何绕过 JavaFX 的 TableView "placeholder"？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16992631/