JavaFX：TreeTableView和扩展没有子项的项目 [英] JavaFX: TreeTableView and expanding items without children

问题描述

我有TreeTableView项目。即使项目没有子项，我希望该用户看到箭头展开。原因很简单 - 懒惰负载。当用户点击箭头程序时检查是否有可能的项目（例如在DB中）。如果此项目的子项存在，则将它们添加到项目中。如果它们不存在，箭头必须消失。怎么做？

I have TreeTableView with items. I want that user see the "arrow" to expand even if item has no children. The reason is very simple - lazy load. When user clicks at arrow program checks if there are possible items (for example in DB). If children for this item exist then they are added to item. If they don't exist the "arrow" must disappear. How to do it?

推荐答案

TreeItem 的Javadocs 显示了一个基本上这样做的例子。您可以覆盖 isLeaf 和 getChildren 方法来懒惰地实例化子项。以下是适用于 TreeTableView 的相同想法：

The Javadocs for TreeItem show an example that basically does this. You can override the isLeaf and getChildren methods to lazily instantiate the children. Here's the same idea adapted for a TreeTableView:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javafx.application.Application;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.ObservableList;
import javafx.event.Event;
import javafx.scene.Scene;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class LazyTreeTable extends Application {

    @Override
    public void start(Stage primaryStage) {
        TreeTableView<Item> treeTable = new TreeTableView<>();
        TreeTableColumn<Item, String> nameCol = new TreeTableColumn<>("Name");
        nameCol.setCellValueFactory(cellData -> cellData.getValue().getValue().nameProperty());
        nameCol.setPrefWidth(250);
        TreeTableColumn<Item, Number> valueCol = new TreeTableColumn<>("Value");
        valueCol.setCellValueFactory(cellData -> cellData.getValue().getValue().valueProperty());
        valueCol.setPrefWidth(150);
        treeTable.getColumns().addAll(Arrays.asList(nameCol, valueCol));

        treeTable.setRoot(new ItemTreeNode(new Item(1)));

        primaryStage.setScene(new Scene(new BorderPane(treeTable), 400, 600));
        primaryStage.show();
    }

    public static class ItemTreeNode extends TreeItem<Item> {
        private boolean childrenLoaded = false ;

        public ItemTreeNode(Item value) {
            super(value);
        }

        @Override
        public boolean isLeaf() {
            if (childrenLoaded) {
                return getChildren().isEmpty() ;
            }
            return false ;
//          return getChildren().isEmpty();
        }

        @Override
        public ObservableList<TreeItem<Item>> getChildren() {
            if (childrenLoaded) {
                return super.getChildren();
            }

            childrenLoaded = true ;
            if (getValue().getValue() < 100_000) {
                List<TreeItem<Item>> children = new ArrayList<>();
                for (int i = 0 ; i < 10; i++) {
                    children.add(new ItemTreeNode(new Item(getValue().getValue() * 10 + i)));
                }
                super.getChildren().addAll(children);
            } else {
                // great big hack:
                super.getChildren().add(null);
                super.getChildren().clear();
            }
            return super.getChildren() ;
        }
    }

    public static class Item {
        private IntegerProperty value = new SimpleIntegerProperty();
        private StringProperty name = new SimpleStringProperty();

        public Item(String name, int value) {
            setName(name);
            setValue(value);
        }

        public Item(int value) {
            this(String.format("Item %,d", value), value);
        }

        public final IntegerProperty valueProperty() {
            return this.value;
        }

        public final int getValue() {
            return this.valueProperty().get();
        }

        public final void setValue(final int value) {
            this.valueProperty().set(value);
        }

        public final StringProperty nameProperty() {
            return this.name;
        }

        public final java.lang.String getName() {
            return this.nameProperty().get();
        }

        public final void setName(final java.lang.String name) {
            this.nameProperty().set(name);
        }


    }

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

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