Having trouble with FolderListener and ListField

[rhen.sn]

Hi all, I'm a newbie on developing application in Blackberry. I have some issues when I try to add items to my ListField.

I've created a class that extends ListField and implements FolderListener interface. All I want is listening to the device inbox , when there a message arrive, I want to append it into my ListField class. Here is my code:

public void messagesAdded(FolderEvent e) {
Store store = Session.getDefaultInstance().getStore();
        Folder[] f = store.list(Folder.INBOX);
        if (f != null && f.length > 0) {
            try {
                //retrieve only the first inbox
                Folder _inbox = f[0];

                Message _msgInbox[] = _inbox.getMessages();
                for (int i = 0; i < _msgInbox.length; i++) {
                    if (_msgInbox[i].getMessageType() == Message.EMAIL_MESSAGE) {
                        System.out.println("Sender :" + _msgInbox[i].getFrom().getName());
                        data.insertElementAt(_msgInbox[i], i);
                        this.insert(i);
                    }
                }
                this.invalidate();
                size = data.size();
                System.out.println("Data size :"+size);

            } catch (MessagingException ex) {
                ex.printStackTrace();
            } catch(IllegalStateException ex){
                System.out.println(ex.getMessage());
            }
        } 
}

I got an

 IllegalStateException

when inserting the data
(

this.insert(i)

)


Can someone give me a clue why this happened ?

[Dougsg38p]

The UI is a single-entrant single-threaded component, and can only be accessed from the event thread.

The FolderListener thread actually belongs to another app (the message app).

A common practice is to:

1. Fire a custom global event to your application, which implements GlobalEventListener
2. From the GlobalEventListener, create a runnable object that performs the UI operation, and call it using UiApplication.invokeLater().

[rhen.sn]

thx doug...... I think you are right. I moved the listener into my main App and it suddenly works... But now I'm facing different problem. When I tested and run it in 9530 simulator, it works fine. But when I deployed on actual device I got java.lang.NullPointerException


Here is my main application code :

public class App extends UiApplication implements FolderListener {

    private MailBoxScreen _main;

    public static void main(String[] args) {
        App instance = new App();
        instance.enterEventDispatcher();
    }

    /** Creates a new instance of App */
    public App() {
        _main = new MailBoxScreen(this);
        pushScreen(_main);
    }

    public void messagesAdded(FolderEvent e) {
        //TODO: append to the vector
        final Message incoming = e.getMessage();
        if (incoming != null) {
            try {
                while (App.this == null) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                }
                App.this.invokeLater(new Runnable() {
                    public void run() {
                        //Dialog.alert("1 new mail received");
                        LED.setState(LED.STATE_BLINKING);
                        Alert.startVibrate(2000);
                        MailBoxScreen.getMailListInstance().refreshMail(incoming);
                    }
                });
            } catch (NullPointerException ex) {
            }
        }
    }

I also has surround each code on method that called from the main application with Exception. Still cannot find where i got the NullPointerException

[Dougsg38p]

Are you running on a 9530 device?

Look at the event log on the device and get the stack trace.

On a trackball device:

<alt> L G L G

On a Storm:

press and hold <?123>, then type " , 5 , 5 "