swing - 在 JavaFX GUI 设计中利用观察者模式

Question

如前所述here在 Swing 环境中，GUI 设计经常使用 observer pattern .经常使用 EventListenerList 中规定的方案，有没有Java FX的例子，比如 Converter ，专注于模式本身？

Answer 1

如前所述here ，JavaFX 体系结构倾向于通过实现 Observable 的类来绑定(bind) GUI 元素。界面。为此，Irina Fedortsova 改编了原版 Converter JavaFX for Swing Developers 第 5 章中的 JavaFX:Implementing a Swing Application in JavaFX .

我已经概括了下面的程序，更新到 Java 8并移除对现在 deprecated builder API 的依赖.在下面的变体中，

一个 DoubleProperty 命名为 meters用作应用程序的Observable模型。

Control 的实例，如 TextField , ComboBox和 Slider ，每个功能都作为模型的 View ，以及为用户提供一种控制交互的方式。

在 ConversionPanel 内, 一个 InvalidationListener添加到 ComboBox更新 TextField根据需要查看模型以反射(reflect)当前选择的 Unit ;一个类似的监听器添加到 TextField在用户键入时更新模型本身。

ConversionPanel 的实例之间共享相同的模型由 Slider ，链接 slider 和任何监听模型的控件。

  slider.valueProperty().bindBidirectional(meters);

每个ComboBox还有一个型号， ObservableList ，用户可以从中选择 Unit 的实例.

代码:

/*
 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package converter;

/**
 * @see http://docs.oracle.com/javafx/2/swing/port-to-javafx.htm
 */
public class Unit {

    String description;
    double multiplier;

    Unit(String description, double multiplier) {
        super();
        this.description = description;
        this.multiplier = multiplier;
    }

    @Override
    public String toString() {
        String s = "Meters/" + description + " = " + multiplier;
        return s;
    }
}

/*
 * Copyright (c) 2012, 2013 Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 */
package converter;

/**
 * @see http://docs.oracle.com/javafx/2/swing/port-to-javafx.htm
 */
import java.text.NumberFormat;
import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.beans.property.DoubleProperty;
import javafx.collections.ObservableList;
import javafx.scene.control.*;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.util.StringConverter;

public class ConversionPanel extends TitledPane {

    private static final int MAX = 10000;
    private static final int DIGITS = 3;

    private final TextField textField = new TextField();
    private final Slider slider = new Slider(0, MAX, 0);
    private final ComboBox<Unit> comboBox;
    private NumberFormat numberFormat = NumberFormat.getNumberInstance();
    private DoubleProperty meters;

    {
        numberFormat.setMaximumFractionDigits(DIGITS);
    }

    private InvalidationListener fromMeters = (Observable o) -> {
        if (!textField.isFocused()) {
            textField.setText(numberFormat.format(meters.get() / getMultiplier()));
        }
    };

    private InvalidationListener toMeters = (Observable o) -> {
        if (textField.isFocused()) {
            try {
                Number n = numberFormat.parse(textField.getText());
                meters.set(n.doubleValue() * getMultiplier());
            } catch (Exception ignored) {
            }
        }
    };

    public ConversionPanel(String title, ObservableList<Unit> units, DoubleProperty meters) {
        setText(title);
        setCollapsible(false);
        comboBox = new ComboBox<>(units);
        comboBox.getSelectionModel().select(0);
        comboBox.setConverter(new StringConverter<Unit>() {

            @Override
            public String toString(Unit t) {
                return t.description;
            }

            @Override
            public Unit fromString(String string) {
                throw new UnsupportedOperationException("Not supported yet.");
            }
        });
        setContent(new HBox(new VBox(textField, slider), comboBox));

        this.meters = meters;
        meters.addListener(fromMeters);
        comboBox.valueProperty().addListener(fromMeters);
        textField.textProperty().addListener(toMeters);
        slider.valueProperty().bindBidirectional(meters);
        fromMeters.invalidated(null);
    }

    /**
     * Returns the multiplier for the currently selected unit of measurement.
     */
    public double getMultiplier() {
        return comboBox.getValue().multiplier;
    }
}

/*
 * Copyright (c) 2012, 2013 Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 */
package converter;

import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

/**
 * @see https://stackoverflow.com/a/31909942/230513
 * @see http://docs.oracle.com/javafx/2/swing/port-to-javafx.htm
 */
public class Converter extends Application {

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

    private final ObservableList<Unit> metricDistances;
    private final ObservableList<Unit> usaDistances;
    private final DoubleProperty meters = new SimpleDoubleProperty(1);

    public Converter() {
        //Create Unit objects for metric distances, and then
        //instantiate a ConversionPanel with these Units.
        metricDistances = FXCollections.observableArrayList(
            new Unit("Centimeters", 0.01),
            new Unit("Meters", 1.0),
            new Unit("Kilometers", 1000.0));

        //Create Unit objects for U.S. distances, and then
        //instantiate a ConversionPanel with these Units.
        usaDistances = FXCollections.observableArrayList(
            new Unit("Inches", 0.0254),
            new Unit("Feet", 0.3048),
            new Unit("Yards", 0.9144),
            new Unit("Miles", 1609.34));
    }

    @Override
    public void start(Stage stage) {
        stage.setScene(new Scene(new VBox(
            new ConversionPanel("Metric System", metricDistances, meters),
            new ConversionPanel("U.S. System", usaDistances, meters))));
        stage.show();
    }
}