无法在JavaFX组合框中强制转换Object

Question

我有这个组合框，用户可以按ID和名称显示数据：

public class Listobject extends Application
{


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

    @Override
    public void start(Stage stage)
    {

        // Insert Some data

        final ComboBox<ListGroupsObj> listGroups = new ComboBox();


        listGroups.setButtonCell(new GroupListCell());
        listGroups.setCellFactory(new Callback<ListView<ListGroupsObj>, ListCell<ListGroupsObj>>()
        {
            @Override
            public ListCell<ListGroupsObj> call(ListView<ListGroupsObj> p)
            {
                return new GroupListCell();
            }
        });

        listGroups.setEditable(true);

        ListGroupsObj ob = ListGroupsObj.newInstance().groupId(12).groupName("Group12");
        listGroups.getItems().addAll(ob);
        ListGroupsObj osb = ListGroupsObj.newInstance().groupId(13).groupName("Group13");
        listGroups.getItems().addAll(osb);
        ListGroupsObj oa = ListGroupsObj.newInstance().groupId(14).groupName("Group14");
        listGroups.getItems().addAll(oa);
        ListGroupsObj oz = ListGroupsObj.newInstance().groupId(15).groupName("Group15");
         listGroups.getItems().addAll(oz);


        // second way to add object
        listGroups.getItems().add(new ListGroupsObj(12, "Group 12"));

        listGroups.setValue(ob);

        // Display the selected Group
        listGroups.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<ListGroupsObj>()
        {

            @Override
            public void changed(ObservableValue<? extends ListGroupsObj> arg0, ListGroupsObj arg1, ListGroupsObj arg2)
            {
                if (arg2 != null)
                {
                    System.out.println("Selected Group: " + arg2.getGroupId() + " - " + arg2.getGroupName());
                }
            }
        });

        final StackPane layout = new StackPane();
        layout.getChildren().add(listGroups);
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 15;");
        stage.setScene(new Scene(layout));
        stage.show();
    }

    class GroupListCell extends ListCell<ListGroupsObj>
    {
        @Override
        protected void updateItem(ListGroupsObj item, boolean empty)
        {
            super.updateItem(item, empty);
            if (item != null)
            {
                setText(item.getGroupId() + " - " + item.getGroupName());
            }
        }
    }

    private List<ListGroupsObj> lisGroups;

    public static class ListGroupsObj
    {

        private int groupId;
        private String groupName;

        public static ListGroupsObj newInstance()
        {
            return new ListGroupsObj();
        }

        public ListGroupsObj()
        {
        }

        public ListGroupsObj(int groupId, String groupName)
        {
            this.groupId = groupId;
            this.groupName = groupName;
        }

        public ListGroupsObj groupId(int groupId)
        {
            this.groupId = groupId;
            return this;
        }

        public ListGroupsObj groupName(String groupName)
        {
            this.groupName = groupName;
            return this;
        }

        public int getGroupId()
        {
            return groupId;
        }

        public String getGroupName()
        {
            return groupName;
        }

        @Override
        public String toString()
        {
            return groupId + " - " + groupName;
        }
    }
}

当我运行代码时，我收到此错误：

Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: java.lang.String cannot be cast to listobject.Listobject$ListGroupsObj
    at listobject.Listobject$2.changed(Listobject.java:79)
    at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.beans.property.ReadOnlyObjectWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyObjectWrapper.java:176)
    at javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:142)
    at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
    at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:145)
    at javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:102)
    at javafx.scene.control.ComboBox$2.changed(ComboBox.java:221)
    at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:105)
    at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
    at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:145)
    at javafx.scene.control.ComboBoxBase.setValue(ComboBoxBase.java:167)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.setTextFromTextFieldIntoComboBoxValue(ComboBoxListViewSkin.java:511)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.access$200(ComboBoxListViewSkin.java:57)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$6.changed(ComboBoxListViewSkin.java:416)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$6.changed(ComboBoxListViewSkin.java:406)
    at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:72)
    at javafx.scene.Node$FocusedProperty.notifyListeners(Node.java:7486)
    at javafx.scene.Node.setFocused(Node.java:7537)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$FakeFocusTextField.setFakeFocus(ComboBoxListViewSkin.java:696)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$2.changed(ComboBoxListViewSkin.java:145)
    at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$2.changed(ComboBoxListViewSkin.java:141)
    at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:72)
    at javafx.scene.Node$FocusedProperty.notifyListeners(Node.java:7486)
    at javafx.scene.Node.setFocused(Node.java:7537)
    at javafx.scene.Scene$KeyHandler.setWindowFocused(Scene.java:3856)
    at javafx.scene.Scene$KeyHandler$1.invalidated(Scene.java:3875)
    at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:135)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:178)
    at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.access$100(ReadOnlyBooleanWrapper.java:148)
    at javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:144)
    at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
    at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:143)
    at javafx.stage.Window.setFocused(Window.java:409)
    at com.sun.javafx.stage.WindowPeerListener.changedFocused(WindowPeerListener.java:59)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:89)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:39)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:130)
    at com.sun.glass.ui.Window.handleWindowEvent(Window.java:1235)
    at com.sun.glass.ui.Window.notifyFocus(Window.java:1210)
    at com.sun.glass.ui.win.WinWindow._setVisible(Native Method)
    at com.sun.glass.ui.Window.setVisible(Window.java:570)
    at com.sun.javafx.tk.quantum.WindowStage.setVisible(WindowStage.java:443)
    at javafx.stage.Window$9.invalidated(Window.java:776)
    at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:109)
    at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:143)
    at javafx.stage.Window.setShowing(Window.java:826)
    at javafx.stage.Window.hide(Window.java:851)
    at com.sun.javafx.stage.WindowCloseRequestHandler.dispatchBubblingEvent(WindowCloseRequestHandler.java:45)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:204)
    at com.sun.javafx.stage.WindowPeerListener.closing(WindowPeerListener.java:80)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:113)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:39)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:130)
    at com.sun.glass.ui.Window.handleWindowEvent(Window.java:1235)
    at com.sun.glass.ui.Window.notifyClose(Window.java:1139)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
    at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
    at java.lang.Thread.run(Thread.java:744)

这一行是问题所在：

listGroups.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<ListGroupsObj>()
        {

            @Override
            public void changed(ObservableValue<? extends ListGroupsObj> arg0, ListGroupsObj arg1, ListGroupsObj arg2)
            {
                if (arg2 != null)
                {
                    System.out.println("Selected Group: " + arg2.getGroupId() + " - " + arg2.getGroupName());
                }
            }
        });

你能帮我解决这个问题吗？

P.S我将添加此转换器：

public class GroupConverter extends StringConverter<ListGroupsObj>
    {

        @Override
        public String toString(ListGroupsObj obj)
        {
            return obj.getGroupId() + " - " + obj.getGroupName();
        }

        @Override
        public ListGroupsObj fromString(String obj)
        {

            //TODO when you type for example "45 - NextGroup" you want to take only tyhe number"
            return ListGroupsObj.newInstance().groupName(obj);
        }

    }

Answer 1

问题是您的ComboBox是可编辑的。当您编辑它（或只是单击它）时，它会尝试将值设置为TextField中用作编辑器的值。该值是一个String：但是您已经创建了ComboBox来存储ListGroupsObj类型的值。

您需要关闭输入值的功能（即不要拨打listGroups.setEditable(true)），或者需要按listGroups.setConverter(...)提供转换器。

Answer 2

彼得使用此代码

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Callback;

/**
 *
 * @author reegan
 */
public class Listobject extends Application {

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

    @Override
    public void start(Stage stage) {

        // Insert Some data

        final ComboBox<ListGroupsObj> listGroups = new ComboBox();


        listGroups.setButtonCell(new GroupListCell());
        listGroups.setCellFactory(new Callback<ListView<ListGroupsObj>, ListCell<ListGroupsObj>>() {
            @Override
            public ListCell<ListGroupsObj> call(ListView<ListGroupsObj> p) {
                return new GroupListCell();
            }
        });

        listGroups.setEditable(true);

        ListGroupsObj ob = ListGroupsObj.newInstance().groupId(12).groupName("Group12");
        listGroups.getItems().addAll(ob);
        ListGroupsObj osb = ListGroupsObj.newInstance().groupId(13).groupName("Group13");
        listGroups.getItems().addAll(osb);
        ListGroupsObj oa = ListGroupsObj.newInstance().groupId(14).groupName("Group14");
        listGroups.getItems().addAll(oa);
        ListGroupsObj oz = ListGroupsObj.newInstance().groupId(15).groupName("Group15");
        listGroups.getItems().addAll(oz);


        // second way to add object
        listGroups.getItems().add(new ListGroupsObj(12, "Group 12"));

        listGroups.setValue(ob);

        // Display the selected Group
//        listGroups.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<ListGroupsObj>() {
//            @Override
//            public void changed(ObservableValue<? extends ListGroupsObj> arg0, ListGroupsObj arg1, ListGroupsObj arg2) {
//                if (arg2 != null) {
//                    listGroups.setEditable(true);
//                    System.out.println("Selected Group: " + arg2.getGroupId() + " - " + arg2.getGroupName());
//                }
//            }
//        });


        listGroups.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Object>() {

            @Override
            public void changed(ObservableValue<? extends Object> ov, Object t, Object t1) {
//                 System.out.println("Selected Group:  " + t1.toString());
                 System.out.println("Selected Group : " + t1);
            }
        });

        final StackPane layout = new StackPane();
        layout.getChildren().add(listGroups);
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 15;");
        stage.setScene(new Scene(layout));
        stage.show();
    }

    class GroupListCell extends ListCell<ListGroupsObj> {

        @Override
        protected void updateItem(ListGroupsObj item, boolean empty) {
            super.updateItem(item, empty);
            if (item != null) {
                setText(item.getGroupId() + " - " + item.getGroupName());
            }
        }
    }
//    private List<ListGroupsObj> lisGroups;

    public static class ListGroupsObj {

        private int groupId;
        private String groupName;

        public static ListGroupsObj newInstance() {
            return new ListGroupsObj();
        }

        public ListGroupsObj() {
        }

        public ListGroupsObj(int groupId, String groupName) {
            this.groupId = groupId;
            this.groupName = groupName;
        }

        public ListGroupsObj groupId(int groupId) {
            this.groupId = groupId;
            return this;
        }

        public ListGroupsObj groupName(String groupName) {
            this.groupName = groupName;
            return this;
        }

        public int getGroupId() {
            return groupId;
        }

        public String getGroupName() {
            return groupName;
        }

        @Override
        public String toString() {
            return groupId + " - " + groupName;
        }

    }
}

Answer 3

将combobox editable设置为false