Question

我有以下问题。我有一个CombBox，它应该显示我的Quiz类的名称（此类还有Tasks的列表），我想从可用的选择中删除每一个Quiz 。我还创建了Quizzes Teacher，我只想在第二个Quizzes中向所选所有者显示相应的ComboBox（我没有到目前为止这个部分的问题。）

这是我的代码。

QuizComboBox

public class QuizComboBox extends ComboBox {

public QuizComboBox() {
    List<Quiz> quizList = new QuizDao().getAllQuizes();

    startTask(quizList);

    Platform.runLater(() -> {
        setCellFactory(new Callback<ListView<Quiz>, ListCell<Quiz>>() {
            @Override
            public ListCell<Quiz> call(ListView<Quiz> arg0) {
                return new ListCell<Quiz>() {
                    @Override
                    protected void updateItem(Quiz item, boolean empty) {
                        super.updateItem(item, empty);

                        if (item == null || empty) {
                            setGraphic(null);
                        } else {
                            String quizText = item.getName();
                            setText(quizText);
                        }
                    }
                };
            }
        });
    });
}

public void startTask(List<Quiz> quizList){
    Runnable task = () -> removeEmptyQuizzes(quizList);
    Thread backgroundThread = new Thread(task);
    backgroundThread.setDaemon(true);
    backgroundThread.start();
}

private void removeEmptyQuizzes(List<Quiz> quizList){
    for(Quiz q : quizList){
        if(q.getTaskList().isEmpty()){
            quizList.remove(q);
        }
    }
    Platform.runLater(() -> setItems(FXCollections.observableArrayList(quizList)));
}

}

以下ComboBox的监听者Teachers更新了项目

    private void teacherComboBoxListener(){
    view.getTeacherComboBox().getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Teacher>() {
        @Override
        public void changed(ObservableValue<? extends Teacher> arg0, Teacher oldValue, Teacher newValue) {

            view.getQuizComboBox().setValue(null);

            if(newValue == view.getAllTeachersChoice()){
                List<Quiz> quizList = new QuizDao().getAllQuizes();
                view.getQuizComboBox().startTask(quizList);
            }
            else {
                Teacher selectedTeacher = (Teacher) view.getTeacherComboBox().getSelectionModel().getSelectedItem();
                List<Quiz> quizList = selectedTeacher.getQuizList();
                view.getQuizComboBox().startTask(quizList);
            }
        }
    });
}

我收到以下异常

  Exception in thread "Thread-5" java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
    at java.util.ArrayList$Itr.next(ArrayList.java:851)
    at view.controlElements.QuizComboBox.removeEmptyQuizzes(QuizComboBox.java:51)
    at view.controlElements.QuizComboBox.lambda$startTask$1(QuizComboBox.java:44)
    at java.lang.Thread.run(Thread.java:745)

编辑：我已经尝试了@ fabian的解决方案，它适用于相当大的错误，它会从我的数据库中删除所有Quizzez空TaskList。

    private void removeEmptyQuizzes(List<Quiz> quizList){
    for(Iterator<Quiz> iterator = quizList.iterator(); iterator.hasNext();){
        Quiz q = iterator.next();
        if(q.getTaskList().isEmpty()){
            iterator.remove(); // removed from db also
        }
    }
    Platform.runLater(() -> setItems(FXCollections.observableArrayList(quizList)));
}

JavaFX中的组合框和并发问题

0 个答案: