如何将焦点监听器放在 JavaFX 中的 Treecell 上？

Question

我正在构建一个应用程序，我需要在显示数据的窗格旁边有一个树视图。当有人在树视图中选择一个项目时，应用程序必须识别他们选择的内容并从数据库中寻找正确的数据，然后以我选择的格式显示它。用户在树形视图中如何选择项目（鼠标单击、Tab 键、箭头键等）必须无关紧要，只要当项目获得焦点时，就会触发一个方法将数据呈现给用户。

我通过以下方式完美地实现了鼠标点击：

    // Application thread method to build the tree map, used in the generateTree
    // method.
    public void treeBuilder(TreeMap<ModelSites, ArrayList<ModelPlants>> map) {
        
        TreeMap<ModelSites, ArrayList<ModelPlants>> treeMap = map;

        final TreeItemProperties<String, String> rootTreeItem = new TreeItemProperties<String, String>("EMT", null);

        TreeItemProperties<String, Integer> site = null;
        TreeItemProperties<String, Integer> plant = null;
        
        for (Map.Entry<ModelSites, ArrayList<ModelPlants>> entry : treeMap.entrySet()) {
            site = new TreeItemProperties<String, Integer>(entry.getKey().getLongName(), entry.getKey().getPrimaryKey());
            rootTreeItem.getChildren().add(site);

            if (site.getValue().equalsIgnoreCase("test item")) {
                site.setExpanded(true);
            }

            for (int i = 0; i < entry.getValue().size(); i++) {
                plant = new TreeItemProperties<String, Integer>(entry.getValue().get(i).getSitePlantId() + " " + entry.getValue().get(i).getShortName(), entry.getValue().get(i).getPrimaryKey());
                site.getChildren().add(plant);
            }
        }
        
        //Cell Factory is used to effectively turn the tree items into nodes, which they are not natively.
        //This is necessary to have actions linked to the tree items (eg. double click an item to open an edit window).
        emtTree.setCellFactory(new Callback<TreeView<String>, TreeCell<String>>() {

            @Override
            public TreeCell<String> call(TreeView<String> param) {
                FactoryTreeCell<String> cell = new FactoryTreeCell<String>();

                cell.setOnMouseClicked(event -> {
                    if (!cell.isEmpty()) {
                        @SuppressWarnings("unchecked")
                        TreeItemProperties<String, Integer> treeItem = (TreeItemProperties<String, Integer>) cell.getTreeItem();
                        generateEquipmentPanes(treeItem.getPropertyValue());
                    }
                });
                return cell;
            }
        });

        rootTreeItem.setExpanded(true);
        emtTree.setRoot(rootTreeItem);
    }

// Populate the main screen with all equipment items in the selected plant.
    public void generateEquipmentPanes(int plantId) {

        int plant = plantId;
        
        Task<LinkedList<ModelEquipment>> task = new Task<LinkedList<ModelEquipment>>() {
            @Override
            public LinkedList<ModelEquipment> call() {
                LinkedList<ModelEquipment> equipmentList = DAOEquipment.listEquipmentByPlant(plant);
                return equipmentList;
            }
        };

        // When list is built successfully, send the results back to the application
        // thread to load the equipment panes in the GUI.
        task.setOnSucceeded(e -> equipmentPaneBuilder(task.getValue()));
        task.setOnFailed(e -> task.getException().printStackTrace());
        task.setOnCancelled(null);

        String methodName = new Object() {}.getClass().getEnclosingMethod().getName();

        Thread thread = new Thread(task);
        thread.setName(methodName);
        //System.out.println("Thread ID: " + thread.getId() + ", Thread Name: " + thread.getName());
        thread.setDaemon(true);
        thread.start();
    }

    // Application thread method to build the equipment panes, used in the
    // generateEquipmentPanes method.
    public void equipmentPaneBuilder(LinkedList<ModelEquipment> list) {
        LinkedList<ModelEquipment> equipmentList = list;
        
        EquipmentPanels.getChildren().clear();

        for (int i = 0; i < equipmentList.size(); i++) {
            ModelEquipment item = equipmentList.get(i);

            try {
                PaneEquipment equipmentPane = new PaneEquipment();
                equipmentPane.updateFields(item.getTechId(), item.getShortName(), item.getLongDesc()); equipmentPane.setId("equipPane" + i);
                            
                EquipmentPanels.getChildren().add(equipmentPane);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

我已经进行了大量的搜索，并且我想出了如何实现侦听器而不是处理程序，因为这似乎是我想要的方式 - 将侦听器放在单元格的属性上。但是当用监听器替换事件处理程序时，就像下面的两个例子，我遇到了很多问题。

                emtTree.getSelectionModel().selectedItemProperty().addListener((observable, oldValue, newValue) -> {
                    if (newValue != null) {
                        @SuppressWarnings("unchecked")
                        TreeItemProperties<String, Integer> treeItem = (TreeItemProperties<String, Integer>) cell.getTreeItem();
                        generateEquipmentPanes(treeItem.getPropertyValue());
                    }
                });

                cell.focusedProperty().addListener(new ChangeListener<Boolean>() {

                    @Override
                    public void changed(ObservableValue<? extends Boolean> observable, Boolean oldValue, Boolean newValue) {
                        if (!cell.isEmpty()) {
                            @SuppressWarnings("unchecked")
                            TreeItemProperties<String, Integer> treeItem = (TreeItemProperties<String, Integer>) cell.getTreeItem();
                            generateEquipmentPanes(treeItem.getPropertyValue());
                        }
                    }
                    
                });

首先，每次单击来自行generateEquipmentPanes(treeItem.getPropertyValue()); 的树项时，我都会得到nullpointerexceptions。其次，它倾向于从错误的项目中选择数据，而不是我选择的项目。然后点击几下后，它似乎完全崩溃了，除了提供更多 nullpointerexceptions 之外什么也不做。

据我了解，我认为问题在于侦听器相对于需要传递给方法generateEquipmentPanes 的变量的位置。还有一些关于在某个时间点移除监听器并在以后重新添加它们的东西。

我应该以某种方式将侦听器放入单元工厂吗？目前它看起来像这样：

import javafx.scene.control.TreeCell;

public class FactoryTreeCell<T> extends TreeCell<T> {
    
    public FactoryTreeCell() {
    }
    
    /*  
     * The update item method simply displays the cells in place of the tree items (which disappear when setCellFactory is set.
     * This can be used for many more things (such as customising appearance) not implemented here.
    */
    @Override
    protected void updateItem(T item, boolean empty) {
        super.updateItem(item, empty);
        
        if (empty || item == null) {
            setText(null);
            setGraphic(null);   //Note that a graphic can be many things, not just an image.  Refer openJFX website for more details.
        } else {
            setText(item.toString());
        }
    }
    
}

我注意到的另一件事是，还有其他方法可以实现Callback，这可能更适合听众，但我不知道该怎么做。

我多年来一直坚持这一点，所以突破会很棒。

Answer 1

您不应该使用树形单元格来检查所选值。您的 ChangeListener 已经直接接收到新值：

emtTree.getSelectionModel().selectedItemProperty().addListener(
    (observable, oldSelection, newSelection) -> {
        if (newSelection != null) {
            TreeItemProperties<String, Integer> treeItem = newSelection;
            generateEquipmentPanes(treeItem.getPropertyValue());
        }
    });