javafx:使用任务更新 UI，然后停止执行

Question

我正在开发一个应用程序来检测网络钓鱼网站，使用 javafx。我有一个“预测”按钮，它在其事件处理程序中执行所有必要的处理。我还希望能够更新 ProgressBar，其中包含有关处理过程中进度的信息。我为此使用了一个任务，调用 updateProgress 和 updateValue 来获取最终结果。

但是，如果发生异常，我想更新 UI，然后立即终止 EventHandler 的执行，使用 updateProgress 和一些错误值。但是，updateProgress 不会立即更新 UI。是否存在某种东西不仅可以从 EventHandler 内部更新 UI(例如 Task)，而且还可以让我准确控制 UI 更新的时间？

作为引用，这是我完整的事件处理程序代码:

 predict.setOnAction(new EventHandler<ActionEvent>() {

        @Override
        public void handle(ActionEvent event)
        {
            Task<Result> task = new Task<Result>()
            {
                @Override
                protected Result call() throws Exception
                {
                    String url = urlText.getText();
                    ArffData arffData = new ArffData();
                    try
                    {
                        updateProgress(1, 10);
                        URL uri = new URL(url);

                        String domain = uri.getHost();
                        arffData.setUrlSimilarity(DataGatherer.readLevenshtein(domain));
                        updateProgress(2, 10);
                        boolean redirection = DataGatherer.getRedirectionStatus(url);

                        arffData.setRedirection(redirection);
                        updateProgress(3, 10);
                        Response response = Jsoup.connect(url).execute();
                        arffData.setSpellingErrors(DataGatherer.getSpellingErrors(response).size());
                    }
                    catch (IOException e1)
                    {
                        updateProgress(-1, 10); //Should update UI before terminating
                        return null;
                    }



                    Classifier rf;
                    Instances instances;
                    try
                    {
                        updateProgress(4, 10);
                        rf = (Classifier) SerializationHelper.read("RF100.model");
                        instances = new DataSource("phishingData.arff").getDataSet();
                    }
                    catch (Exception e1)
                    {
                        updateProgress(-1, 10);
                        return null;
                    }
                    if (instances.classIndex() == -1)
                        instances.setClassIndex(instances.numAttributes() - 1);
                    String offers = offerText.getValue();
                    String lf = lfText.getValue();
                    updateProgress(5, 10);
                    Instance inst = InstanceSetup.setUpInstance(arffData, offers, lf, instances);

                    try
                    {
                        updateProgress(6, 10);
                        double clsLabel = rf.classifyInstance(inst);
                        instances.add(inst); 
                        rf.buildClassifier(instances);
                        SerializationHelper.write("RF100.model", rf);
                        Evaluation eval = new Evaluation(instances);
                        eval.crossValidateModel(rf, instances, 10, new Random(1));
                        boolean phishing = clsLabel ==0 ?true: false;
                        Result result = new Result(phishing, eval.pctCorrect());
                        updateProgress(10, 10);
                        if(clsLabel == 0)
                        {
                            predictionLabel.setText("the given website IS a phishing website.");
                        }
                        else
                        {
                            predictionLabel.setText("the given website IS NOT a phishing website.");
                        }
                        updateValue(result);
                        accuracyLabel.setText("PhishGuard is " + String.format("%.4f%%", eval.pctCorrect()) + 
                                " confident in this prediction.");
                        return result;

                    }
                    catch (Exception e)
                    {
                        updateProgress(-1, 10);
                        return null;
                    }

                }                   
            };

            task.progressProperty().addListener(new ChangeListener<Number>()
            {

                @Override
                public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue)
                {
                    switch(newValue.intValue())
                    {
                        case 1:
                        {
                            pBar.setProgress(10);
                            progressLabel.setText(progressLabels[1]);
                        }
                        case 2:
                        {
                            pBar.setProgress(30);
                            progressLabel.setText(progressLabels[2]);
                        }
                        case 3:
                        {
                            pBar.setProgress(50);
                            progressLabel.setText(progressLabels[3]);
                        }
                        case 4:
                        {
                            pBar.setProgress(70);
                            progressLabel.setText(progressLabels[4]);
                        }
                        case 5:
                        {
                            pBar.setProgress(80);
                            progressLabel.setText(progressLabels[5]);                               
                        }
                        case 6:
                        {
                            pBar.setProgress(90);
                            progressLabel.setText(progressLabels[6]);
                        }
                        case 10:
                        {
                            pBar.setProgress(100);
                            progressLabel.setText(progressLabels[0]);
                        }
                        case -1:
                        {
                            predictionLabel.setText("a prediction could not be made.");
                            accuracyLabel.setText("");
                            pBar.setProgress(0);
                            progressLabel.setText(progressLabels[0]);
                        }

                    }


                }

            });

            task.valueProperty().addListener(new ChangeListener<Result>(){

                @Override
                public void changed(ObservableValue<? extends Result> observable, Result oldValue, Result newValue)
                {
                    // TODO Auto-generated method stub
                    boolean phishing = newValue.isPhishing();
                    if(phishing)
                    {
                        predictionLabel.setText("the given website IS a phishing website.");
                    }
                    else
                    {
                        predictionLabel.setText("the given website IS NOT a phishing website.");
                    }

                    accuracyLabel.setText("PhishGuard is " + String.format("%.4f%%", newValue.getAccuracy()) + 
                            " confident in this prediction.");

                }

            });
            new Thread(task).start();
        }});

Answer 1

Task 的 progressProperty()和 ProgressBar要么是不确定，要么设置为 0 到 1(含)之间的值。对于进度条:

A positive value between 0 and 1 indicates the percentage of progress where 0 is 0% and 1 is 100%. Any value greater than 1 is interpreted as 100%.

所以当你观察任务的进度值，然后获取intValue()时，只有三种可能:-1(当进度不确定时)、1(任务完成时)或 0(所有其他值)。当您使用任务的 progressProperty 注册监听器时，它已经处于 INDETERMINATE 状态，因此您看到的第一个更改具有 intValue() 0(与您的任何情况都不匹配)，并且所有后续更改都会看到相同的值，直到任务完成(当您看到 1 时)。此时，您将进度条的进度设置为 10，如上所述，它被解释为 100%。

可能您真正想要做的只是将进度条的进度属性绑定(bind)到任务的进度属性(这样它们就会一起增加)。

要定期更新文本，您可以使用任务的 messageProperty 。

因此，我将完全删除任务进度属性上的监听器，并将其替换为

pBar.progressProperty().bind(task.progressProperty());
pBar.textProperty().bind(task.messageProperty());

根据任务中需要的每条消息调用 updateMessage()(稍后编写代码)。

为此:

However, in the event of an exception, I want to update the UI then immediately terminate execution of the EventHandler

我假设您的真正意思是“终止任务的执行”，因为事件处理程序早已完成。正如注释中所述，Task 默认情况下处理异常。因此，您可以让异常从 call() 方法传播，并在 onFailed 处理程序中执行 UI 更新。

结果看起来像这样:

predict.setOnAction(new EventHandler<ActionEvent>() {

    @Override
    public void handle(ActionEvent event)
    {
        Task<Result> task = new Task<Result>()
        {
            @Override
            protected Result call() throws Exception
            {
                String url = urlText.getText();
                ArffData arffData = new ArffData();

                updateProgress(1, 10);
                updateMessage(progressLabels[1]);
                URL uri = new URL(url);

                String domain = uri.getHost();
                arffData.setUrlSimilarity(DataGatherer.readLevenshtein(domain));
                updateProgress(2, 10);
                updateMessage(progressLabels[2]);

                boolean redirection = DataGatherer.getRedirectionStatus(url);

                arffData.setRedirection(redirection);
                updateProgress(3, 10);
                updateMessage(progressLabels[3]);
                Response response = Jsoup.connect(url).execute();
                arffData.setSpellingErrors(DataGatherer.getSpellingErrors(response).size());






                Classifier rf;
                Instances instances;

                updateProgress(4, 10);
                updateMessage(progressLabels[4]);
                rf = (Classifier) SerializationHelper.read("RF100.model");
                instances = new DataSource("phishingData.arff").getDataSet();
                if (instances.classIndex() == -1)
                    instances.setClassIndex(instances.numAttributes() - 1);
                String offers = offerText.getValue();
                String lf = lfText.getValue();
                updateProgress(5, 10);
                updateMessage(progressLabels[5]);

                Instance inst = InstanceSetup.setUpInstance(arffData, offers, lf, instances);

                updateProgress(6, 10);
                updateMessage(progressLabels[6]);

                double clsLabel = rf.classifyInstance(inst);
                instances.add(inst); 
                rf.buildClassifier(instances);
                SerializationHelper.write("RF100.model", rf);
                Evaluation eval = new Evaluation(instances);
                eval.crossValidateModel(rf, instances, 10, new Random(1));
                boolean phishing = clsLabel ==0 ?true: false;
                Result result = new Result(phishing, eval.pctCorrect());
                updateProgress(10, 10);
                updateMessage(progressLabels[0]);

                if(clsLabel == 0)
                {
                    predictionLabel.setText("the given website IS a phishing website.");
                }
                else
                {
                    predictionLabel.setText("the given website IS NOT a phishing website.");
                }
                updateValue(result);
                accuracyLabel.setText("PhishGuard is " + String.format("%.4f%%", eval.pctCorrect()) + 
                        " confident in this prediction.");
                return result;


            }                   
        };

        pBar.progressProperty().bind(task.progressProperty());
        pLabel.textProperty().bind(task.messageProperty());


        task.valueProperty().addListener(new ChangeListener<Result>(){

            @Override
            public void changed(ObservableValue<? extends Result> observable, Result oldValue, Result newValue)
            {
                // TODO Auto-generated method stub
                boolean phishing = newValue.isPhishing();
                if(phishing)
                {
                    predictionLabel.setText("the given website IS a phishing website.");
                }
                else
                {
                    predictionLabel.setText("the given website IS NOT a phishing website.");
                }

                accuracyLabel.setText("PhishGuard is " + String.format("%.4f%%", newValue.getAccuracy()) + 
                        " confident in this prediction.");

            }

        });

        task.setOnFailed(e -> {
            predictionLabel.setText("a prediction could not be made.");
            accuracyLabel.setText("");
            pBar.progressProperty().unbind();
            pBar.setProgress(0);
            progressLabel.setText(progressLabels[0]);
        });

        new Thread(task).start();
    }});