JavaFX ListView单元格工厂项呈现完成事件

任务: 检查项目是否在ListView的可见区域中。

解决方案: 我有JavaFX ListView,其中包含要渲染的项。为了找出哪些项目在ListView的可见区域中,我实现了计算显示给用户的项目数量的单元工厂。

1、增加项目
2.检查是否在ListView中可见。

问题是: 为了计算项目,项目添加线程(调用线程)必须等待单元工厂完成项目添加操作和渲染。然而,我不知道如何实现它,因为调用线程不知道JavaFX UI线程何时使用内部量子工具包机制完成渲染。 单元格工厂项在JavaFX内的独立线程中呈现,JavaFX无法与之同步。

添加粗略的调用线程延迟解决了一个问题,它清楚地表明了线程同步问题,但我需要更优雅和清晰的解决方案。

    public class MessengerServiceContext {
        @Override
        public void messageReceived(final MessageReceivedEvent messageReceivedEvent) {
            ...        

            //Calling thread method
            messengerServiceControl.receiveMessage(messengerMessageData);   

            //Main thread is paused for several seconds to wait JavaFX UI threads.
            //Ugly and erroneous
            //Demonstrates the cause of the problem
            try {
                Thread.sleep(2000);
            } catch (InterruptedException ex) { Logger.getLogger(MessengerServiceControl.class.getName()).log(Level.SEVERE, null, ex);
            }

            if (!messengerServiceControl.getMessageElementControlVisibility(messengerMessageData)) {
                int newMessagesCount = getNewMessagesCount().get();
                getNewMessagesCount().set(++newMessagesCount);
            }
        }
    }

    public class MessengerServiceControl implements Initializable {
        ...
        private TrackingListCellFactory<MessageElementControl> messengerOutputWindowListViewCellFactory;
        ...

        //Calling (message processing) thread method which inserts ListView item
        public void receiveMessage(final MessengerMessageData messengerMessageData) { 
            //Calling MessengerServiceControl model method to insert items in ListView using JavaFX UI thread
            MessageElementControl messageElementControl = model.createMessage(messengerMessageData, false);

            //Tried scene and parent property
           messageElementControl.sceneProperty().addListener((observable, oldValue, newValue) -> {
             if (newValue != null) {
                 if (!getMessageElementControlVisibility(messengerMessageData)) {
                     int newMessagesCount = getNewMessagesCount().get();                               
                     getNewMessagesCount().set(++newMessagesCount);
                 }
             }
         }

         boolean getMessageElementControlVisibility(final MessengerMessageData messengerMessageData) {
            return messengerOutputWindowListViewCellFactory.getItemVisibility(messengerMessageData);
         }

         //Cell factory class which is responsible for items rendering:
         private static class TrackingListCellFactory<T extends MessageElementControl> implements Callback<ListView<T>, ListCell<T>> {
             //Items which have cells visible to the user
             private final Set<T> visibleItems = new HashSet();

             TrackingListCellFactory() {    
             }

             boolean getItemVisibility(final MessengerMessageData messengerMessageData) {
                 synchronized (this) {
                     Optional<T> messageElementControlOptional = visibleItems.stream().filter((item) -> {
                         return item.getMessageData().getMessageCreatedDate().isEqual(messengerMessageData.getMessageCreatedDate());
                     }).findFirst();

                     return messageElementControlOptional.isPresent();
                 }
             } 

             @Override
             public ListCell<T> call(ListView<T> param) {
                 //Create cell that displays content
                 ListCell<T> cell = new ListCell<T>() {
                     @Override
                     protected void updateItem(T item, boolean empty) {
                         super.updateItem(item, empty);

                         if (!empty && item != null) {
                             setGraphic(item);
                         }
                     }
                 };            

                 //Add and remove item when cell is reused for different item
                 cell.itemProperty().addListener((observable, oldItem, newItem) -> { 
                     synchronized (TrackingListCellFactory.this) {
                         if (oldItem != null) {
                             visibleItems.remove(oldItem);
                         }

                         if (newItem != null) {
                             visibleItems.add(newItem);
                         }                
                     }
                 });

                 //Update set when bounds of item change
                 ChangeListener<Object> boundsChangeHandler = (observable, oldValue, newValue) -> {
                     synchronized (TrackingListCellFactory.this) {
                         T item = cell.getItem();

                         if (item != null) {
                             visibleItems.add(item);
                         }
                     }
                 });

                 //Must update either if cell changes bounds, or if cell moves within scene (e.g.by scrolling)  
           cell.boundsInLocalProperty().addListener(boundsChangeHandler);  
   cell.localToSceneTransformProperty().addListener(boundsChangeHandler);                     

             return cell;                                               
             }
         }
     }