NullPointerException while fast updating TextField

Question

I'm working on an app, that searches some files in the directed folder and prints them in TableView<myFile> foundFilesList, that is stored in the Main class. myFile just extends File a bit. The searching is done using service in background thread, that puts found data to ObservableList<myFile> filesOfUser. I want to display current amount of find files in TextField foundFilesAmount in the same view, where TableView with files is located -- ResultsView

To do that, I added a ListChangeListener for foundFilesList to ResultsView controller, that uses method setText to print current size of filesOfUser. It looks like:

Main.filesOfUser.addListener(new ListChangeListener<myFile>() {
        @Override
        public void onChanged(Change<? extends myFile> c) {
               while (c.next()){
                  if (c.wasAdded())
                        setCounter(c.getAddedSize());    
              }
        }
});

void setCounter (int number) contains only

  int currValue = Integer.valueOf(foundFilesAmount.getText());
  foundFilesAmount.setText(String.valueOf(currValue + number));

And now what the problem is. Textfield with current amount of find files is updated very fast, and from one moment it stops doing it. In the console I see lots of repeated NullPointerException's from JavaFX Application Thread. Its' contents:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.text.PrismTextLayout.getRuns(PrismTextLayout.java:236)
at javafx.scene.text.Text.getRuns(Text.java:317)
at javafx.scene.text.Text.updatePGText(Text.java:1465)
at javafx.scene.text.Text.impl_updatePeer(Text.java:1500)
at javafx.scene.Node.impl_syncPeer(Node.java:503)
at javafx.scene.Scene$ScenePulseListener.synchronizeSceneNodes(Scene.java:2290)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2419)
at com.sun.javafx.tk.Toolkit.lambda$runPulse$30(Toolkit.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:354)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:381)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:510)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:490)
at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$404(QuantumToolkit.java:319)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)

I tried to set sort of delay before using setText, like updating value in foundFilesAmount only after 5'th, 10'th, 15'th update, etc. But if the search works longer, exceptions are still thrown.

Is there a correct method to show current amount of found files, that contains real amount and doesn't cause so much exceptions?

Thanks in advance.

Answer 1

The correct way is not doing the updates of the UI on a thread other than the application thread. This can otherwise lead to issues with rendering/layouting.

You could use a Task to do the updates to the updates however:

Task<ObservableList<myFile>> task = new Task<
Task<ObservableList<myFile>>() {
    @Override
    protected ObservableList<myFile> call() throws Exception {
        ObservableList<myFile> files = FXCollections.observableArrayList();

        while (...) {
            ...
            files.add(...);
            updateMessage(Integer.toString(files.size()));
            ...
        }

        return files;
    }
};
task.setOnSucceeded(evt -> tableView.setItems(task.getValue()));
Thread t = new Thread(task);
textField.textProperty().bind(task.messageProperty());
t.setDaemon(true);

t.start();

Answer 2

try something like this:

    Platform.runLater(new Runnable() {
        @Override
        public void run() {
            // update your JavaFX controls here
        }
    });