如何从 ObservableValue 获取调用者阶段<? extends Boolean>焦点变化监听器

Question

我希望将焦点侦听器作为静态变量传递给 throw 静态方法，它的功能是在该阶段失去焦点时关闭该阶段。

我有代码：

主班

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        FXMLLoader loader = new FXMLLoader(getClass().getResource("sample.fxml"));
        Scene scene = new Scene(loader.load(), 565, 551);
        primaryStage.setScene(scene);
        Controller controller = loader.getController();
        primaryStage.show();
        controller.setStage1InitOwner();
    }

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

控制器类

 public class Controller implements Initializable {
    @FXML
    private AnchorPane anchorPane;

    // stage1 suppose to be a small dialogs
    private final Stage stage1 = new Stage();

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        stage1.setScene(new Scene(new Pane(new Label("a Dialog")), 200, 200));

        // giving the listener to stage1 from static method
        stage1.focusedProperty().addListener(Prepare.getFocusListener());
        stage1.initStyle(StageStyle.TRANSPARENT);
    }

    public void setStage1InitOwner() {
        stage1.initOwner(anchorPane.getScene().getWindow());
        stage1.show();
    }
}

准备类（里面的静态方法和变量）

  public class Prepare  {
    public static ChangeListener<Boolean> focusListener = new ChangeListener<Boolean>() {
        @Override
        public void changed(ObservableValue<? extends Boolean> observableValue, Boolean aBoolean, Boolean t1) {
            if (!t1) ;
            // get the stage from observableValue and close it when focus is lost.
        }
    };
    public static ChangeListener<Boolean> getFocusListener()
    {
        return focusListener;
    }
}

.xml 文件

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

<?import javafx.scene.layout.*?>

<AnchorPane fx:id="anchorPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="551.0" prefWidth="565.0" style="-fx-background-color: #fffe00;" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
   </children>
</AnchorPane>

现在我想从 ChangeListener 中的 ObservableValue 中获取调用者阶段。 我试图将它转换为 BooleanProperty 然后使用 getBean()

 if (!t1) {
            BooleanProperty booleanProperty = (BooleanProperty) observableValue;
            Stage stage = (Stage) booleanProperty.getBean();
            stage.close();
        }

，但我收到以下错误：

    Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: class javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl cannot be cast to class javafx.beans.property.BooleanProperty (javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl and javafx.beans.property.BooleanProperty are in module javafx.base of loader 'app')
    at sample.Prepare$1.changed(Prepare.java:13)
    at sample.Prepare$1.changed(Prepare.java:9)
    at javafx.base/com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:360)
    at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.base/javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:78)
    at javafx.base/javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:103)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:111)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
    at javafx.graphics/javafx.stage.Window.setFocused(Window.java:678)
    at javafx.graphics/javafx.stage.Window$1.setFocused(Window.java:150)
    at javafx.graphics/com.sun.javafx.stage.WindowHelper.setFocused(WindowHelper.java:112)
    at javafx.graphics/com.sun.javafx.stage.WindowPeerListener.changedFocused(WindowPeerListener.java:64)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:126)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:40)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.lambda$handleWindowEvent$4(GlassWindowEventHandler.java:178)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:176)
    at javafx.graphics/com.sun.glass.ui.Window.handleWindowEvent(Window.java:1336)
    at javafx.graphics/com.sun.glass.ui.Window.notifyFocus(Window.java:1315)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    at java.base/java.lang.Thread.run(Thread.java:833)
Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: class javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl cannot be cast to class javafx.beans.property.BooleanProperty (javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl and javafx.beans.property.BooleanProperty are in module javafx.base of loader 'app')
    at sample.Prepare$1.changed(Prepare.java:13)
    at sample.Prepare$1.changed(Prepare.java:9)
    at javafx.base/com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:360)
    at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.base/javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:78)
    at javafx.base/javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:103)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:111)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
    at javafx.graphics/javafx.stage.Window.setFocused(Window.java:678)
    at javafx.graphics/javafx.stage.Window$1.setFocused(Window.java:150)
    at javafx.graphics/com.sun.javafx.stage.WindowHelper.setFocused(WindowHelper.java:112)
    at javafx.graphics/com.sun.javafx.stage.WindowPeerListener.changedFocused(WindowPeerListener.java:64)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:126)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:40)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.lambda$handleWindowEvent$4(GlassWindowEventHandler.java:178)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:176)
    at javafx.graphics/com.sun.glass.ui.Window.handleWindowEvent(Window.java:1336)
    at javafx.graphics/com.sun.glass.ui.Window.notifyFocus(Window.java:1315)
    at javafx.graphics/com.sun.glass.ui.win.WinWindow._close(Native Method)
    at javafx.graphics/com.sun.glass.ui.Window.close(Window.java:352)
    at javafx.graphics/com.sun.glass.ui.win.WinWindow.close(WinWindow.java:316)
    at javafx.graphics/com.sun.javafx.tk.quantum.WindowStage.lambda$close$4(WindowStage.java:824)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithRenderLock(QuantumToolkit.java:442)
    at javafx.graphics/com.sun.javafx.tk.quantum.WindowStage.close(WindowStage.java:817)
    at javafx.graphics/javafx.stage.Window$12.invalidated(Window.java:1157)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
    at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
    at javafx.graphics/javafx.stage.Window.setShowing(Window.java:1190)
    at javafx.graphics/javafx.stage.Window.hide(Window.java:1215)
    at javafx.graphics/com.sun.javafx.stage.WindowCloseRequestHandler.dispatchBubblingEvent(WindowCloseRequestHandler.java:45)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/com.sun.javafx.stage.WindowPeerListener.closing(WindowPeerListener.java:93)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:147)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:40)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.lambda$handleWindowEvent$4(GlassWindowEventHandler.java:178)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:176)
    at javafx.graphics/com.sun.glass.ui.Window.handleWindowEvent(Window.java:1336)
    at javafx.graphics/com.sun.glass.ui.Window.notifyClose(Window.java:1241)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    at java.base/java.lang.Thread.run(Thread.java:833)

那么问题是什么，以及获得舞台的最佳方式是什么。

非常感谢 StackOverflow 团队。

Answer 1

错误告诉你出了什么问题：

 java.lang.ClassCastException: class javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl cannot be cast to class javafx.beans.property.BooleanProperty (javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl and javafx.beans.property.BooleanProperty are in module javafx.base of loader 'app')

您正在尝试将ReadOnlyBooleanProperty实例强制转换为BooleanProperty ，这显然是不可能的。 但是您实际上并不需要处理这种“狭窄”的实现。 您所关心的只是获取“bean”，并且只需要类型为ReadOnlyProperty<?> （这是属性类层次结构的顶部）。

ChangeListener<Boolean> listener = (obs, wasFocused, isFocused) -> {
  if (!isFocused) {
    var property = (ReadOnlyProperty<?>) obs;
    var stage = (Stage) property.getBean();
    stage.close();
  }
};

但是，您根本不需要处理铸造问题。 如果您的目标是简单地避免代码重复，那么只需创建一个接受Stage并将侦听器添加到其focused属性的实用程序方法。

例如：

import javafx.beans.value.ChangeListener;
import javafx.stage.Stage;

public final class CloseOnFocusLost {

  private static final Object KEY = new Object();

  public static void installListener(Stage stage) {
    @SuppressWarnings("unchecked")
    var listener = (ChangeListener<Boolean>) stage.getProperties().get(KEY);
    if (listener == null) {
      listener = (obs, wasFocused, isFocused) -> {
        if (!isFocused) {
          stage.close();
        }
      };
      stage.getProperties().put(KEY, listener);
      stage.focusedProperty().addListener(listener):
    }
  }

  public static void uninstallListener(Stage stage) {
    @SuppressWarnings("unchecked")
    var listener = (ChangeListener<Boolean>) stage.getProperties().remove(KEY);
    if (listener != null) {
      stage.focusedProperty().removeListener(listener):
    }
  }

  // prevent instantiation of utility class
  private CloseOnFocusLost() {}
}

与您的代码相比，上述内容有一些优点：

• 它更加类型安全。
  • 您的代码容易受到第二个ClassCastException的攻击，因为可以将侦听器添加到不属于Stage的属性。
• 您不必处理强制转换，因为您可以直接访问Stage实例。
• 它具有防止向同一focused属性添加多个侦听器的保护措施。

如果您不关心最后一点，并且不需要删除侦听器，那么您可以将代码简化为以下内容：

import javafx.stage.Stage;

public final class CloseOnFocusLost {

  public static void installListener(Stage stage) {
    stage.focusedProperty().addListener((obs, wasFocused, isFocused) -> {
      if (!isFocused) {
        stage.close();
      }
    });
  }

  // prevent instantiation of utility class
  private CloseOnFocusLost() {}
}

在任何一种情况下，您都需要添加 close-on-focus-lost 侦听器：

CloseOnFocusLost.installListener(theStageInstance);

Answer 2

一个简单的可执行应用程序，演示了Slaw 的回答中的一些技术，以及一两个以上的技术。 我不会对这些技术添加任何额外的解释，因为这在 Slaw 的回答中已经很好地涵盖了。

此示例中只有最后一个选项以编程方式演示确保侦听器不会多次添加到同一阶段。

import javafx.application.Application;
import javafx.beans.property.ReadOnlyProperty;
import javafx.beans.value.ChangeListener;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.stage.Stage;

public class StageClosureApp extends Application {
    private static final ChangeListener<Boolean> CLOSE_ON_FOCUS_LOSS_USING_BEAN_LISTENER =
            (o, wasFocused, isFocused) -> {
                if (!isFocused) ((Stage) ((ReadOnlyProperty<?>) o).getBean()).close();
            };

    private static ChangeListener<Boolean> closeOnFocusLossListener(Stage stage) {
        return (o, wasFocused, isFocused) -> {
            if (!isFocused) stage.close();
        };
    }

    private static void closeOnFocusLoss(Stage stage) {
        stage.focusedProperty().removeListener(CLOSE_ON_FOCUS_LOSS_USING_BEAN_LISTENER);
        stage.focusedProperty().addListener(CLOSE_ON_FOCUS_LOSS_USING_BEAN_LISTENER);
    }

    @Override
    public void start(Stage stage) {
        // all options perform the same function (close the stage on losing focus).
        // when testing, only enable one option, commenting the others out.

        // option 1: use a closure to reference the stage in a lambda function defined inline.
        stage.focusedProperty().addListener((o, wasFocused, isFocused) -> {
            if (!isFocused) stage.close();
        });

        // option 2: pass the stage instance to a static listener generation function.
        stage.focusedProperty().addListener(closeOnFocusLossListener(stage));

        // option 3: get the stage from the bean in an inline lambda function.
        stage.focusedProperty().addListener((o, wasFocused, isFocused) -> {
            if (!isFocused) ((Stage) ((ReadOnlyProperty<?>) o).getBean()).close();
        });

        // option 4: use a single instance static change listener that get the stage from the bean.
        stage.focusedProperty().addListener(CLOSE_ON_FOCUS_LOSS_USING_BEAN_LISTENER);

        // option 5: update stage to add a focus loss listener when it is not focused (can safely be called multiple time for a stage)
        closeOnFocusLoss(stage);
            
        stage.setScene(new Scene(new Label("hello, world")));
        stage.show();
    }
    
    public static void main(String[] args) {
        launch();
    }
}

如果失去焦点的阶段是应用程序中显示的唯一阶段（就像在这些测试用例中一样），则默认情况下，一旦失去焦点，应用程序将根据应用程序生命周期自动关闭.

我不确定这个例子对 Slaw 的回答有多大帮助，但它可能有用，所以我暂时保留这个帖子。