FXML 为 ComboBox 和 TableView 动态初始化 ObservableList

Question

我正在尝试制作 Dan Nicks 在 对 this question 的评论 中提出的自定义生成器。
这个想法是在构造它之前设置组合的数据。
combo.fxml:

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.ComboBox?>

<ComboBox  fx:id="combo1" items="${itemLoader.items}"  prefWidth="150.0" 
   xmlns:fx="http://javafx.com/fxml/1">
</ComboBox>

提供数据的class：

public class ComboLoader {

    public ObservableList<Item> items;

    public ComboLoader() {

        items = FXCollections.observableArrayList(createItems());
    }

    private List<Item> createItems() {
            return IntStream.rangeClosed(0, 5)
                    .mapToObj(i -> "Item "+i)
                    .map(Item::new)
                    .collect(Collectors.toList());
        }

    public ObservableList<Item> getItems(){

        return items;
    }

    public static class Item {

        private final StringProperty name = new SimpleStringProperty();

        public Item(String name) {
            this.name.set(name);
        }

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

测试：

public class ComboTest extends Application {

    @Override
    public void start(Stage primaryStage) throws IOException {

        primaryStage.setTitle("Populate combo from custom builder");

        Group group = new Group();

        GridPane grid = new GridPane();
        grid.setPadding(new Insets(25, 25, 25, 25));
        group.getChildren().add(grid);

        FXMLLoader loader = new FXMLLoader();
        ComboBox combo = loader.load(getClass().getResource("combo.fxml"));
        loader.getNamespace().put("itemLoader", new ComboLoader());
        grid.add(combo, 0, 0);

        Scene scene = new Scene(group, 450, 175);

         primaryStage.setScene(scene);
         primaryStage.show();
    }

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

没有产生错误，但没有填充组合。
缺少什么？

顺便说一句：TableView 的类似解决方案工作正常：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.TableView?>
<?import javafx.scene.control.TableColumn?>
<?import javafx.scene.control.cell.PropertyValueFactory?>

 <TableView items="${itemLoader.items}"   xmlns:fx="http://javafx.com/fxml/1">
     <columns>
         <TableColumn text="Item">
             <cellValueFactory><PropertyValueFactory property="name" /></cellValueFactory>
         </TableColumn>
     </columns>
 </TableView>

Answer 1

编辑了 kleopatra 的以下评论：
使用以下加载程序可以使用字符串加载问题中给出的 combo.fxml：

//load observable list with strings
public class ComboStringLoader {

    private final ObservableList<String> items;

    public ComboStringLoader() {
        items = FXCollections.observableArrayList(createStrings());
    }

    private List<String> createStrings() {
            return IntStream.rangeClosed(0, 5)
                    .mapToObj(i -> "String "+i)
                    .map(String::new)
                    .collect(Collectors.toList());
    }

    //name of this method corresponds to itemLoader.items in xml.
    //if xml name was itemLoader.a this method should have been getA(). 
    public ObservableList<String> getItems(){
        return items;
    }
}

以类似的方式加载具有 Item 个实例的组合仅意味着 Item#toString 对于组合中的文本：

//load observable list with Item#toString
public class ComboObjectLoader1 {

    public ObservableList<Item> items;

    public ComboObjectLoader1() {
        items = FXCollections.observableArrayList(createItems());
    }

    private List<Item> createItems() {
        return IntStream.rangeClosed(0, 5)
                .mapToObj(i -> "Item "+i)
                .map(Item::new)
                .collect(Collectors.toList());
    }

    public ObservableList<Item> getItems(){
        return items;
    }
}

其中项目定义为：

class Item {

    private final StringProperty name = new SimpleStringProperty();

    public Item(String name) {
        this.name.set(name);
    }

    public final StringProperty nameProperty() {
        return name;
    }

    @Override
    public String toString() {
        return name.getValue();
    }
}

更好的方法是使用自定义加载组合 ListCell<item>:

//load observable list with custom ListCell
public class ComboObjectLoader2 {

    private final ObservableList<ItemListCell> items;

    public ComboObjectLoader2() {
        items =FXCollections.observableArrayList (createCells());
    }

    private List<ItemListCell> createCells() {
            return IntStream.rangeClosed(0, 5)
                    .mapToObj(i -> "Item "+i)
                    .map(Item::new)
                    .map(ItemListCell::new)
                    .collect(Collectors.toList());
    }

    public ObservableList<ItemListCell> getItems(){
        return items;
    }
}

class ItemListCell extends ListCell<Item> {

    private final Label text;

    public ItemListCell(Item item) {
        text = new Label(item.nameProperty().get());
        setGraphic(new Pane(text));
    }

    @Override
    public void updateItem(Item item, boolean empty) {
        super.updateItem(item, empty);
        if (empty) {
            setText(null);
            setGraphic(null);
        } else {
            text.setText(item.nameProperty().get());
        }
    }
}

最后但并非最不重要的替代方法是将自定义 ListCell<Item> 设置为组合的细胞工厂。
这可以通过向 fxml 文件添加控制器来完成：
combo2.fxml:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.ComboBox?>
<ComboBox fx:id="combo1" items="${itemLoader.items}" prefWidth="150.0" xmlns:fx="http://javafx.com/fxml/1" 
      xmlns="http://javafx.com/javafx/10.0.1" fx:controller="test.ComboObjectLoaderAndController">
</ComboBox>

其中 ComboObjectLoaderAndController 既是加载程序又是控制器：

//loads observable list with Items and serves as controller to set cell factory
public class ComboObjectLoaderAndController {

    public ObservableList<Item> items;
    @FXML ComboBox<Item> combo1;

    public ComboObjectLoaderAndController() {
        items = FXCollections.observableArrayList(createItems());
    }

    @FXML
    public void initialize() {
        combo1.setCellFactory(l->new ItemListCell());
    }

    private List<Item> createItems() {
        return IntStream.rangeClosed(0, 5)
                .mapToObj(i -> "Item "+i)
                .map(Item::new)
                .collect(Collectors.toList());
    }

    public ObservableList<Item> getItems(){
        return items;
    }

    class ItemListCell extends  ListCell<Item>{

        @Override
        public void updateItem(Item item, boolean empty) {
            super.updateItem(item, empty);
            if (empty) {
                setText(null);
                setGraphic(null);
            } else {
                setText(item.nameProperty().get());
            }
        }
    }
}

编辑：
在之后我添加了一个通用自定义 ListCell

public class ObjectListCell<T> extends ListCell<T> {

    Function<T,String> textSupplier;

    public  ObjectListCell(Function<T,String> textSupplier) {
        this.textSupplier = textSupplier;
    }

    public Callback<ListView<T>, ListCell<T>> getFactory() {
        return cc -> new ObjectListCell<>(textSupplier);
    }

    public ListCell<T> getButtonCell() {
        return getFactory().call(null);
    }

    @Override
    public void updateItem(T t, boolean empty) {
        super.updateItem(t, empty);
        if (t== null || empty) {
            setText(null);
            setGraphic(null);
        } else {
            setText(textSupplier.apply(t));
        }
    }
}

工厂设置在fxml文件中：
combo3.fxml:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.ComboBox?>
<ComboBox fx:id="combo1" items="${itemLoader.items}"  cellFactory="${cellFactoryProvider.factory}" 
   buttonCell = "${cellFactoryProvider.buttonCell}"
   prefWidth="150.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/10.0.1">
</ComboBox>

测试class:

public class ComboTest extends Application {

    @Override
    public void start(Stage primaryStage) throws IOException {

        primaryStage.setTitle("Populate combo from custom builder");

        //Combo of Strings
        FXMLLoader loader = new FXMLLoader(getClass().getResource("combo.fxml"));
        loader.getNamespace().put("itemLoader", new ComboStringLoader());
        ComboBox<String>stringCombo = loader.load();

        //Combo of Item
        loader = new FXMLLoader(getClass().getResource("combo.fxml"));
        loader.getNamespace().put("itemLoader", new ComboObjectLoader1());
        ComboBox<Item>objectsCombo1 = loader.load();

        //Combo of custom ListCell
        loader = new FXMLLoader(getClass().getResource("combo.fxml"));
        loader.getNamespace().put("itemLoader", new ComboObjectLoader2());
        ComboBox<ItemListCell>objectsCombo2 = loader.load();

        //Combo of Item with custom ListCell factory
        loader = new FXMLLoader(getClass().getResource("combo2.fxml"));
        loader.getNamespace().put("itemLoader", new ComboObjectLoaderAndController());
        ComboBox<Item>objectsCombo3 = loader.load();

        //Combo of Item with custom ListCell factory. Factory is set in FXML
        loader = new FXMLLoader(getClass().getResource("combo3.fxml"));
        loader.getNamespace().put("itemLoader", new ComboObjectLoader1());
        loader.getNamespace().put("cellFactoryProvider", new ObjectListCell<Item>(t -> t.nameProperty().get()));
        ComboBox<Item>objectsCombo4 = loader.load();

        HBox pane = new HBox(25, stringCombo, objectsCombo1,objectsCombo2, objectsCombo3, objectsCombo4);
        pane.setPadding(new Insets(25, 25, 25, 25));

        Scene scene = new Scene(pane, 550, 175);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

Answer 2

从吹毛求疵开始，我做了一些关于如何实际实施我在对的评论中概述的内容的实验。

基本思想是对 listCell 遵循与数据相同的方法，即通过命名空间配置内容和外观（我今天的学习项目）。成分：

可配置的通用自定义 listCell，具有将项目转换为文本的功能
通用“cellFactory 工厂”class 用于提供创建该单元的 cellFactory

cell/factory:

public class ListCellFactory<T> {
    
    private Function<T, String> textProvider;

    public ListCellFactory(Function<T, String> provider) {
        this.textProvider = provider;
    }

    public Callback<ListView<T>, ListCell<T>> getCellFactory() {
        return cc -> new CListCell<>(textProvider);
    }
    
    public ListCell<T> getButtonCell() {
        return getCellFactory().call(null);
    }
    
    public static class CListCell<T> extends ListCell<T> {
        
        private Function<T, String> converter;

        public CListCell(Function<T, String> converter) {
            this.converter = Objects.requireNonNull(converter, "converter must not be null");
        }

        @Override
        protected void updateItem(T item, boolean empty) {
            super.updateItem(item, empty);
            if (empty) {
                setText(null);
            } else {
                setText(converter.apply(item));
            }
        }
        
    }

}

用于创建和配置组合的 fxml：

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.ComboBox?>

<ComboBox  fx:id="combo1" items="${itemLoader.items}"  
    cellFactory="${cellFactoryProvider.cellFactory}" 
    buttonCell = "${cellFactoryProvider.buttonCell}"
    prefWidth="150.0" 
   xmlns:fx="http://javafx.com/fxml/1">
</ComboBox>

使用示例：

public class LocaleLoaderApp extends Application {

    private ComboBox<Locale> loadCombo(Object itemLoader, Function<Locale, String> extractor) throws IOException {
        FXMLLoader loader = new FXMLLoader(getClass().getResource("comboloader.fxml"));
        loader.getNamespace().put("itemLoader", itemLoader);
        loader.getNamespace().put("cellFactoryProvider", new ListCellFactory<Locale>(extractor));
        ComboBox<Locale> combo = loader.load();
        return combo;
    }
    
    @Override
    public void start(Stage primaryStage) throws IOException {

        primaryStage.setTitle("Populate combo from custom builder");

        Group group = new Group();
        GridPane grid = new GridPane();
        grid.setPadding(new Insets(25, 25, 25, 25));
        group.getChildren().add(grid);
        LocaleProvider provider = new LocaleProvider();
        grid.add(loadCombo(provider, Locale::getDisplayName), 0, 0);
        grid.add(loadCombo(provider, Locale::getLanguage), 1, 0);
        Scene scene = new Scene(group, 450, 175);

        primaryStage.setScene(scene);
        primaryStage.show();
    }
    
    public static class LocaleProvider {
        ObservableList<Locale> locales = FXCollections.observableArrayList(Locale.getAvailableLocales());
        
        public ObservableList<Locale> getItems() {
            return locales;
        }
    }
    

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

FXML 为 ComboBox 和 TableView 动态初始化 ObservableList

FXML Dynamically initialize ObservableList for ComboBox and TableView

javafx

items

loader

fxml

observablelist