java - 尝试清除 JavaFX ObservableMap 时出现 ConcurrentException

Question

我正在向我的 JavaFX 8 应用程序添加一些加速器，当我尝试清除场景的加速器时，我遇到了 ConcurrentModificationException。让我解释一下，而不是为每个对话框使用一个场景，我创建了一个伪对话框，它只是一个带有覆盖的 Pane 。添加 Pane 时，将删除旧 Pane 的加速器并添加新 Pane 的加速器。当对话框关闭时，旧的加速器将恢复:

public abstract class DialogController{

    private Map<KeyCombination, Runnable> accelerators;
    .
    .
    .

    protected final void loadMainPane() throws IOException {
        .
        .
        .
        pane.sceneProperty().addListener(new ChangeListener<Scene>() {
            @Override
            public void changed(ObservableValue<? extends Scene> observableValue, Scene oldScene, Scene newScene) {
                if (newScene != null)
                    enableAccelerators();
                else
                    disableAccelerators(oldScene);
            }
        });
    }

    protected void enableAccelerators() {
        accelerators = new HashMap<KeyCombination, Runnable>(pane.getScene().getAccelerators());
        pane.getScene().getAccelerators().clear();
        pane.getScene().getAccelerators().put(new KeyCodeCombination(KeyCode.ENTER, KeyCombination.ALT_DOWN), new Runnable() {
            @Override
            public void run() {
                submit(null);
            }
        });
    }

    protected void disableAccelerators(Scene scene) {
        scene.getAccelerators().putAll(accelerators);
    }
}

当子类需要添加新的加速器时，他们只需要覆盖 enableAccelerators() 方法，调用 super 并添加所需的新加速器。但是，有时，当 enableAccelerators 尝试清除场景的加速器时，会抛出此异常:

java.util.ConcurrentModificationException: null
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
at java.util.HashMap$EntryIterator.next(HashMap.java:1463)
at java.util.HashMap$EntryIterator.next(HashMap.java:1461)
at com.sun.javafx.collections.ObservableMapWrapper$ObservableEntrySet$1.next(ObservableMapWrapper.java:588)
at com.sun.javafx.collections.ObservableMapWrapper$ObservableEntrySet$1.next(ObservableMapWrapper.java:576)
at com.sun.javafx.scene.KeyboardShortcutsHandler.processAccelerators(KeyboardShortcutsHandler.java:340)
at com.sun.javafx.scene.KeyboardShortcutsHandler.dispatchBubblingEvent(KeyboardShortcutsHandler.java:168)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3949)
at javafx.scene.Scene$KeyHandler.access$2100(Scene.java:3896)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:2036)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2493)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:170)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:123)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:197)
at com.sun.glass.ui.View.handleKeyEvent(View.java:517)
at com.sun.glass.ui.View.notifyKey(View.java:927)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.access$200(GtkApplication.java:48)
at com.sun.glass.ui.gtk.GtkApplication$6$1.run(GtkApplication.java:149)
at java.lang.Thread.run(Thread.java:745)

我怀疑我的代码正在清除加速器，而 JavaFX 正在迭代它。我尝试将清除部分放在同步块(synchronized block)中，但它不起作用:

protected void enableAccelerators() {
    accelerators = new HashMap<KeyCombination, Runnable>(pane.getScene().getAccelerators());
    synchronized (pane.getScene().getAccelerators()){
        pane.getScene().getAccelerators().clear();
    }
    pane.getScene().getAccelerators().put(new KeyCodeCombination(KeyCode.ENTER, KeyCombination.ALT_DOWN), new Runnable() {
        @Override
        public void run() {
            submit(null);
        }
    });
}

如何避免这个问题？

Answer 1

您可能需要将更新加速器的代码放入 Platform.runLater() 调用中。尝试

        public void changed(ObservableValue<? extends Scene> observableValue, Scene oldScene, Scene newScene) {
            Platform.runLater(() -> {
                if (newScene != null)
                    enableAccelerators();
                else
                    disableAccelerators(oldScene);
            });
        }

如果 FX 应用程序线程在处理事件时调用您的代码，那么可以想象(如您所建议的)它会在迭代加速器集合时这样做。使用 Platform.runLater() 将导致您的代码在处理完 FX 应用程序线程上当前挂起的任何内容后执行。

(如果这看起来有点像 hack，好吧，被指控有罪......)