binding - 无法设置 Javafx 组合框绑定(bind)值异常

Question

我正在尝试使用带有单元工厂的 javafx 组合框来呈现列表，我在我的 CellList 的覆盖 updateItem() 上使用 setText，但是当我更改基础模型的值时我发现了，这不会影响组合框上的已部署列表。所以我尝试让它绑定(bind)两个属性并且它有效但是当尝试清除选择时我有一个异常。这是代码:

    import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
import javafx.util.Callback;

public class BasicComboBoxSample extends Application {
    public static void main(String[] args) { launch(args); }

    @Override public void start(Stage stage) {
        final Employee john = new Employee("John");
        final Employee jill = new Employee("Jill");
        final Employee jack = new Employee("Jack");

        final ComboBox<Employee> cboEmployees = new ComboBox();

        cboEmployees.getItems().addAll(john, jill, jack);
        cboEmployees.setValue(jill);

        Button b = new Button("ChangeName");
        b.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                john.setName("Maria");
            }
        });

        Button c = new Button("Clear");
        c.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                cboEmployees.getSelectionModel().clearSelection();
            }
        });

        Button d = new Button("Select First");
        d.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                cboEmployees.getSelectionModel().select(john);
            }
        });

        Callback<ListView<Employee>, ListCell<Employee>> cellFactory = new Callback<ListView<Employee>, ListCell<Employee>>() {
            @Override
            public ListCell<Employee> call(ListView<Employee> listView) {
                return new EmployeeListCell();  //To change body of implemented methods use File | Settings | File Templates.
            }
        };

        cboEmployees.setButtonCell(new EmployeeListCell());
        cboEmployees.setCellFactory(cellFactory);

        final StackPane layout = new StackPane();
        VBox v = new VBox();

        v.getChildren().add(cboEmployees);
        v.getChildren().add(b);
        v.getChildren().add(c);
        v.getChildren().add(d);
        layout.getChildren().add(v);

        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 15;");
        stage.setScene(new Scene(layout));
        stage.show();
    }

    class Employee {
        public Employee(String name) { this.setName(name); }
        private SimpleStringProperty name = new SimpleStringProperty("");

        String getName() {
            return name.get();
        }

        SimpleStringProperty nameProperty() {
            return name;
        }

        void setName(String name) {
            this.name.set(name);
        }
    }


    public class EmployeeListCell extends ListCell<Employee> {

        @Override
        protected void updateItem(Employee emp, boolean b) {
            super.updateItem(emp, b);
            if(emp != null){
                textProperty().bind(emp.nameProperty());
            }
        }
    }
}

异常是:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: A bound value cannot be set.
at javafx.beans.property.StringPropertyBase.set(StringPropertyBase.java:157)
at javafx.beans.property.StringPropertyBase.set(StringPropertyBase.java:67)
at javafx.beans.property.StringProperty.setValue(StringProperty.java:84)
at javafx.scene.control.Labeled.setText(Labeled.java:135)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.updateDisplayText(ComboBoxListViewSkin.java:420)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.updateDisplayNode(ComboBoxListViewSkin.java:399)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.getDisplayNode(ComboBoxListViewSkin.java:229)
at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.updateDisplayArea(ComboBoxBaseSkin.java:125)
at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.handleControlPropertyChanged(ComboBoxBaseSkin.java:120)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.handleControlPropertyChanged(ComboBoxListViewSkin.java:198)
at com.sun.javafx.scene.control.skin.SkinBase$3.changed(SkinBase.java:282)
at javafx.beans.value.WeakChangeListener.changed(WeakChangeListener.java:107)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:367)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:100)
at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:123)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:130)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:163)
at javafx.scene.control.ComboBoxBase.setValue(ComboBoxBase.java:148)
at javafx.scene.control.ComboBox.updateValue(ComboBox.java:416)
at javafx.scene.control.ComboBox.access$300(ComboBox.java:166)
at javafx.scene.control.ComboBox$6.changed(ComboBox.java:401)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:367)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:100)
at javafx.beans.property.ReadOnlyObjectWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyObjectWrapper.java:195)
at javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:161)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:130)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:163)
at javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:101)
at javafx.scene.control.ComboBox$ComboBoxSelectionModel$1.invalidated(ComboBox.java:448)
at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:155)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:100)
at javafx.beans.property.ReadOnlyIntegerWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:195)
at javafx.beans.property.ReadOnlyIntegerWrapper.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:161)
at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:130)
at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:163)
at javafx.scene.control.SelectionModel.setSelectedIndex(SelectionModel.java:67)
at javafx.scene.control.SingleSelectionModel.updateSelectedIndex(SingleSelectionModel.java:208)
at javafx.scene.control.SingleSelectionModel.clearSelection(SingleSelectionModel.java:67)
at de.thomasbolz.javafx.BasicComboBoxSample$2.handle(BasicComboBoxSample.java:45)
at de.thomasbolz.javafx.BasicComboBoxSample$2.handle(BasicComboBoxSample.java:42)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Node.fireEvent(Node.java:6863)
at javafx.scene.control.Button.fire(Button.java:179)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3328)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3168)
at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3123)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1563)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2265)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:250)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:173)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:292)
at com.sun.glass.ui.View.handleMouseEvent(View.java:528)
at com.sun.glass.ui.View.notifyMouse(View.java:922)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication$3$1.run(GtkApplication.java:82)
at java.lang.Thread.run(Thread.java:722)

Answer 1

如果 emp 为 null，您需要取消绑定(bind) textProperty