JavaFX ComboBox 更改值导致 IndexOutOfBoundsException [英] JavaFX ComboBox change value causes IndexOutOfBoundsException

问题描述

我想检查我的组合框以限制对某些值的访问".我可以从列表中删除那些无法访问的项目，是的，但我希望用户看到其他选项，即使他(还)无法选择它们.

I want to include checks for my combobox to restrict "access" to some of the values. I could just remove those unaccessible items from the list, yes, but I'd like the user to see the other options, even if he can't select them (yet).

问题:在更改侦听器中选择另一个值会导致 IndexOutOfBoundsException，我不知道为什么.

Problem: Selecting another value inside a changelistener causes an IndexOutOfBoundsException, and I have no idea why.

这是一个 SSCCE.它创建一个带有整数值的 ComboBox，默认情况下选择第一个.然后我尽量保持简单:值的每次更改都被视为错误"，我将选择更改回第一个元素.但是，IndexOutOfBounds:

Here is a SSCCE. It creates a ComboBox with Integer values, and the first one is selected on default. Then I tried to keep it very easy: Every change of the value is considered as "wrong" and I change the selection back to the first element. But still, IndexOutOfBounds:

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.stage.Stage;

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

    @Override
    public void start(Stage stage) throws Exception {
        ComboBox<Integer> box = new ComboBox<Integer>();
        ObservableList<Integer> vals= FXCollections.observableArrayList(0,1,2,3);

        box.setItems(vals);
        box.getSelectionModel().select(0);
        /*box.valueProperty().addListener((observable, oldValue, newValue) -> {
            box.getSelectionModel().select(0);
        });*/
        /*box.getSelectionModel().selectedItemProperty().addListener((observable,oldValue,newValue)->{
            System.out.println(oldValue+","+newValue);
            box.getSelectionModel().select(0);
        });*/

        box.getSelectionModel().selectedIndexProperty().addListener((observable,oldValue,newValue)->{
            System.out.println(oldValue+","+newValue);
            box.getSelectionModel().select(0);
        });
        Scene scene = new Scene(new Group(box),500,500);
        stage.setScene(scene);
        stage.show();
    }
}

我使用 valueProperty、selectedItemProperty 和 selectedIndexProperty 以及所有这些进行了测试:

I tested it with valueProperty, selectedItemProperty and selectedIndexProperty, as well as all of these:

box.getSelectionModel().select(0);

box.getSelectionModel().selectFirst();

box.getSelectionModel().selectPrevious();

box.setValue(0);

if (oldValue.intValue() < newValue.intValue())
            box.getSelectionModel().select(oldValue.intValue());

唯一可行的想法是设置值本身:

The only think that works is setting the value itself:

box.getSelectionModel().select(box.getSelectionModel().getSelectedIndex());
box.setValue(box.getValue));

这里有一个例外:

Exception in thread "JavaFX Application Thread" java.lang.IndexOutOfBoundsException
    at com.sun.javafx.scene.control.ReadOnlyUnbackedObservableList.subList(Unknown Source)
    at javafx.collections.ListChangeListener$Change.getAddedSubList(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ListViewBehavior.lambda$new$178(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ListViewBehavior$$Lambda$126/644961012.onChanged(Unknown Source)
    at javafx.collections.WeakListChangeListener.onChanged(Unknown Source)
    at com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(Unknown Source)
    at com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(Unknown Source)
    at com.sun.javafx.scene.control.ReadOnlyUnbackedObservableList.callObservers(Unknown Source)
    at javafx.scene.control.MultipleSelectionModelBase.clearAndSelect(Unknown Source)
    at javafx.scene.control.ListView$ListViewBitSetSelectionModel.clearAndSelect(Unknown Source)
    at com.sun.javafx.scene.control.behavior.CellBehaviorBase.simpleSelect(Unknown Source)
    at com.sun.javafx.scene.control.behavior.CellBehaviorBase.doSelect(Unknown Source)
    at com.sun.javafx.scene.control.behavior.CellBehaviorBase.mousePressed(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Scene$MouseHandler.process(Unknown Source)
    at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
    at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$350(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$$Lambda$172/2037973250.get(Unknown Source)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.notifyMouse(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda$36/2117255219.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

我做错了什么?

推荐答案

在 JavaFX 中，您不能在更改正在进行时更改 ObservableList 的内容.这里发生的事情是您的侦听器(您尝试的任何侦听器)作为 box.getSelctionModel().getSelectedItems() ObservableList 更改的一部分被触发.所以基本上，您不能在处理选择更改时更改选择.

In JavaFX, you cannot change the contents of an ObservableList while a change is already in progress. What is happening here is that your listeners (any of the ones you try) are being fired as part of the box.getSelctionModel().getSelectedItems() ObservableList changing. So basically, you cannot change the selection while a selection change is being processed.

无论如何，您的解决方案有点笨拙.如果您在所选项目(或组合框值)上有另一个侦听器，即使您的方法有效，它也会暂时看到带有非法"选择的组合框.例如，在上面的示例中，如果用户尝试选择1"，另一个侦听器会看到选择更改为不允许的值1"，然后又回到0".处理不应在此侦听器中允许的值可能会使您的程序逻辑非常复杂.

Your solution is a bit unwieldy anyway. If you had another listener on the selected item (or combo box value), even if your method worked it would temporarily see the combo box with an "illegal" selection. E.g in the example above, if the user tries to select "1", another listener would see the selection change to the disallowed value "1", then back to "0". Dealing with values that are not supposed to be allowed in this listener would likely make your program logic pretty complex.

恕我直言，更好的方法是防止用户选择不允许的值.您可以使用设置单元的 disable 属性的单元工厂来执行此操作:

A better approach, imho, is to prevent the user from selecting the disallowed values. You can do this with a cell factory that sets the disable property of the cell:

    box.setCellFactory(lv -> new ListCell<Integer>() {
        @Override
        public void updateItem(Integer item, boolean empty) {
            super.updateItem(item, empty);
            if (empty) {
                setText(null);
            } else {
                setText(item.toString());
                setDisable(item.intValue() != 0);
            }
        }
    });

在外部样式表中包含以下内容会给用户通常的视觉提示，即项目不可选择:

Including the following in an external style sheet will give the user the usual visual hint that the items are not selectable:

.combo-box-popup .list-cell:disabled  {
    -fx-opacity: 0.4 ;
}

这篇关于JavaFX ComboBox 更改值导致 IndexOutOfBoundsException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！