FileObserver class always has null value for path in OnEvent(FileObserverEvents e, String path)

Question

This question is extension of this question. Posting another question because that is closed.

I am implementing the FileObserver Class as mentioned by @SushiHangover but when the event (OnEvent) is fired then the value of path is null and the value of e is 1073741856.

This is how I am initializing the FileObserver as suggested by @SushiHangover

[Activity(Label = "Main Menu")]
public class MainView : MvxActivity
{
    public MusicFolderObserver MusicFolderObserver;

    protected override void OnViewModelSet()
    {
        File musicFolder = new File(Environment.GetExternalStoragePublicDirectory(Environment.DirectoryMusic), "/MyFolder");
        MusicFolderObserver = new MusicFolderObserver (musicFolder.AbsolutePath);
        MusicFolderObserver.StartWatching();
        SetContentView(Resource.Layout.View_Main);
    }
}

and following is the File observer Class

public class MusicFolderObserver : FileObserver
{

    static FileObserverEvents _Events = (FileObserverEvents.AllEvents);
    const string tag = "StackoverFlow";

    public MusicFolderObserver (String rootPath) : base(rootPath, _Events)
    {
        Log.Info(tag, String.Format("Watching : {0}", rootPath));
    }

    public MusicFolderObserver (String rootPath, FileObserverEvents events) : base(rootPath, events)
    {
        Log.Info(tag, String.Format("Watching : {0} : {1}", rootPath, events));
    }

    public override void OnEvent(FileObserverEvents e, String path)
    {
        Log.Info(tag, String.Format("{0}:{1}", path, e));
    }
}

Please let me know how can I make this observer active for the entire duration the app is running. I am trying to make an app which is active 24/7 and triggers if there is any change in the observed Music folder

score 0 · Answer 1 · answered Sep 08 '17 at 05:11

A FileObserverEvents of 1073741856 contains a FileObserverEvents.Openflag:

if (e.HasFlag(FileObserverEvents.Open))
{
    Log.Debug(tag, $"File Opened : {path}");
}

When Android (Linux) manipulates a file in a directory you might get a series of events as it alters the contents of the directory, a lot of these actions (FileObserverEvents) will have no path attached to them and those can be ignored in your case (if you want details of all the event flags when you get a null path, consult a Linux file system reference).

`OnEvent` override example:

public override void OnEvent(FileObserverEvents e, String path)
{
    if (path == null) return;
    Log.Debug(tag, $"{path} : {e}");
}

`Touch` a new file:

adb shell touch /sdcard/Music/MyFolder/BohemianRhapsody100.mp3

Results in:

SO      : BohemianRhapsody100.mp3 : Create
SO      : BohemianRhapsody100.mp3 : Open
SO      : BohemianRhapsody100.mp3 : CloseNowrite

Moving a file:

adb shell mv /sdcard/Music/MyFolder/BohemianRhapsody100.mp3 /sdcard/Music/MyFolder/BohemianRhapsody101.mp3

Results in:

SO      : BohemianRhapsody100.mp3 : MovedFrom
SO      : BohemianRhapsody101.mp3 : MovedTo

Deleting a file:

adb shell rm /sdcard/Music/MyFolder/BohemianRhapsody101.mp3

Results in:

SO      : BohemianRhapsody101.mp3 : Delete

etc....

FileObserver class always has null value for path in OnEvent(FileObserverEvents e, String path)

1 Answers1

OnEvent override example:

Touch a new file:

Moving a file:

Deleting a file:

`OnEvent` override example:

`Touch` a new file: