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Question

我有一个Label需要显示ObservableList. 我有IntegerBinding设置，但我还需要Label根据列表中的元素数量调整 的措辞。

对于下面的 MCVE，如果列表中只有一个元素，则应显示“列表包含 1 个项目”。但是如果列表为空或包含多个项目，则“项目”需要是复数形式：“列表包含 3 个项目”。

我尝试使用三元运算符和 a 来这样做BooleanBinding，但两者都没有任何效果，因为三元表达式似乎只计算一次。单击“添加”按钮不会更改Label.

编码

import javafx.application.Application;

import javafx.beans.binding.Bindings;

import javafx.beans.binding.IntegerBinding;

import javafx.collections.FXCollections;

import javafx.collections.ObservableList;

import javafx.geometry.Insets;

import javafx.geometry.Pos;

import javafx.scene.Scene;

import javafx.scene.control.Button;

import javafx.scene.control.Label;

import javafx.scene.layout.VBox;

import javafx.stage.Stage;

public class Main extends Application {

    ObservableList<String> items = FXCollections.observableArrayList();

    private IntegerBinding listSize = Bindings.size(items);

    public static void main(String[] args) {

        launch(args);

    }

    @Override

    public void start(Stage primaryStage) {

        // Simple Interface

        VBox root = new VBox(10);

        root.setAlignment(Pos.CENTER);

        root.setPadding(new Insets(10));

        Label label = new Label();

        // Bind the label to display a size-aware notification

        label.textProperty().bind(

                Bindings.concat("The list contains ", listSize,

                        ((items.size() != 1) ? " items!" : " item!"))

        );

        // Button to add items

        Button button = new Button("Add");

        button.setOnAction(event -> items.add("new item"));

        root.getChildren().addAll(label, button);

        // Show the stage

        primaryStage.setScene(new Scene(root));

        primaryStage.setTitle("Sample");

        primaryStage.show();

    }

}

当列表的大小发生变化时，我是否需要包含一个侦听器？

Answer 1

这是使用自定义 StringBinding() 的快速解决方案// Bind the label to display a size-aware notificationlabel.textProperty().bind(new StringBinding() {&nbsp; &nbsp; { bind(listSize); }&nbsp; &nbsp; @Override&nbsp; &nbsp; protected String computeValue() {&nbsp; &nbsp; &nbsp; &nbsp; return "The list contains " + listSize.get() + ((items.size() != 1) ? " items!" : " item!");&nbsp; &nbsp; }});在上面的代码中，您将监听 listSize 的更改，然后您将在 computeValue() 中创建新的 String。

Answer 2

这是较短的等价物：label.textProperty().bind(Bindings.createStringBinding(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; () -> "The list contains " + listSize.get() + ((itemSize.get() != 1) ? " items!" : " item!",&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; listSize&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ));或者另一种选择：label.textProperty.bind(Bindings&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.when(listSize.isEqualTo(1))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.then("The list contains 1 item!")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.otherwise(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Bindings.concat("The list contains " + listSize + " items!")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;);