Question

I tried to listen file change event in BlackBerry base on FileExplorer example, but whenever I added or deleted file, it always showed “Deferring persistence as device is being used” and I can’t catch anything .
Here is my code:

public class FileChangeListenner implements FileSystemJournalListener{

private long _lastUSN; // = 0;     
public void fileJournalChanged() {
    long nextUSN = FileSystemJournal.getNextUSN();
    String msg = null;       
    for (long lookUSN = nextUSN - 1; lookUSN >= _lastUSN && msg == null; --lookUSN) 
    {
        FileSystemJournalEntry entry = FileSystemJournal.getEntry(lookUSN);
        // We didn't find an entry
        if (entry == null) 
        { 
            break;
        }
        // Check if this entry was added or deleted
        String path = entry.getPath();            
        if (path != null) 
        {  
            switch (entry.getEvent()) 
            {
                case FileSystemJournalEntry.FILE_ADDED:
                    msg = "File was added.";                       
                    break;

                case FileSystemJournalEntry.FILE_DELETED:
                    msg = "File was deleted.";
                    break;
            }
        }
    }        
    _lastUSN = nextUSN;        
    if ( msg != null ) 
    {           
        System.out.println(msg);
    }
}
}

Here is the caller:

Thread t = new Thread(new Runnable() {
            public void run() {
                new FileChangeListenner();
                try {
                    Thread.sleep(5000);
                    createFile();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }                   
            }
        });
        t.start();

Create file method worked fine:

   private void createFile() {
    try {
        FileConnection fc = (FileConnection) Connector
                .open("file:///SDCard/newfile.txt");
        // If no exception is thrown, then the URI is valid, but the file
        // may or may not exist.
        if (!fc.exists()) {
            fc.create(); // create the file if it doesn't exist
        }
        OutputStream outStream = fc.openOutputStream();
        outStream.write("test content".getBytes());
        outStream.close();
        fc.close();
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

and output:

 0:00:44.475: Deferring persistence as device is being used.
 0:00:46.475: AG,+CPT
 0:00:46.477: AG,-CPT
 0:00:54.476: VM:+GC(f)w=11
 0:00:54.551: VM:-GCt=9,b=1,r=0,g=f,w=11,m=0
 0:00:54.553: VM:QUOT t=1
 0:00:54.554: VM:+CR
 0:00:54.596: VM:-CR t=5
 0:00:55.476: AM: Exit net_rim_bb_datatags(291)
 0:00:55.478: Process net_rim_bb_datatags(291) cleanup started
 0:00:55.479: VM:EVTOv=7680,w=20
 0:00:55.480: Process net_rim_bb_datatags(291) cleanup done
 0:00:55.481: 06/25 03:40:41.165 BBM FutureTask Execute: net.rim.device.apps.internal.qm.bbm.platform.BBMPlatformManagerImpl$3@d1e1ec79
 0:00:55.487: 06/25 03:40:41.171 BBM FutureTask Finish : net.rim.device.apps.internal.qm.bbm.platform.BBMPlatformManagerImpl$3@d1e1ec79

I also tried to remove the thread or create or delete file in simulator ‘s sdcard directly but it doesn’t help.
Please tell me where is my problem. Thanks

Answer 1

You instantiate the FileChangeListenner, but you never register it, and also don’t keep it as a variable anywhere. You probably need to add this call

FileChangeListenner listener = new FileChangeListenner();
UiApplication.getUiApplication().addFileSystemJournalListener(listener);

You also might need to keep a reference (listener) around for as long as you want to receive events. But maybe not (the addFileSystemJournalListener() call might do that). But, you at least need that call to addFileSystemJournalListener(), or you’ll never get fileJournalChanged() called back.