Question

I am having the following problem:

In my Activity, I have a listview that lists the content of the external files directory.
i want the list to be updated as soon as any kind of change occurs in the content, so I have:

public class FileAdapter implements ListAdapter {
    private File mDirectory;
    private FileObserver mFileObserver;
    private DataSetObservable mDataSetObservable;

    public FileAdapter() {
    super();
    this.mDirectory =
        new ContextWrapper(ImportList.this).getExternalFilesDir(null);
        if (this.mDirectory != null) {
            this.mFileObserver = 
                new FileObserver(this.mDirectory.getAbsolutePath()) {
                    @Override
                    public void onEvent(int event, String path) {
                        new Handler().post(new Runnable() {
                            public void run() {
                                FileAdapter.this.mDataSetObservable.notifyChanged();
                            }
                        });
                    }
                };
        }
        this.mDataSetObservable = new DataSetObservable();
    }
    public void startWatching() {
        this.mFileObserver.startWatching();
    }

    public void stopWatching() {
        this.mFileObserver.stopWatching();
    }

    public boolean areAllItemsEnabled() {
        return true;
    }

    public boolean isEnabled(int position) {
        return true;
    }

    public int getCount() {
        return this.mDirectory == null ? 0 : this.mDirectory.listFiles().length;
    }

    public Object getItem(int arg0) {
        return this.mDirectory.listFiles()[arg0];
    }

    public long getItemId(int position) {
        return position;
    }

    public int getItemViewType(int position) {
        return 0;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        ItemView itemView;
        if (convertView == null) {
            itemView = new ItemView(ImportList.this, 1);
        } else {
            itemView = (ItemView) convertView;
        }
        File file = (File) this.getItem(position);
        itemView.setValue(0, file.getName());
        return itemView;
    }

    public int getViewTypeCount() {
        return 1;
    }

    public boolean hasStableIds() {
        return false;
    }

    public boolean isEmpty() {
        return this.getCount() < 1;
    }

    public void registerDataSetObserver(DataSetObserver observer) {
        this.mDataSetObservable.registerObserver(observer);
    }

    public void unregisterDataSetObserver(DataSetObserver observer) {
        this.mDataSetObservable.unregisterObserver(observer);
    }

    public String getPath() {
        return this.mDirectory == null ?
            ImportList.this.getResources().getString(R.string.no_external_files) :
            this.mDirectory.getAbsolutePath();
    }
}

as an inner class of my Activity

and in my onCreate I do:

this.mFileBrowser = (ListView) this.findViewById(R.id.listview_filebrowser);
....
this.mFileAdapter = new FileAdapter();
this.mFileBrowser.setAdapter(this.mFileAdapter);

And in onResume() I do:

this.mFileAdapter.startWatching();

So as I understand, this should cause my ListView to automatically reload as soon as a file is deleted from the external files directory, for example.
But it doesn’t work!

Answer 1

As DJC said, the fileobserver is not recursive. If you do a good search on google, you’ll find a RecursiveFileObserver Class that works very well. One thing I did with it, however, is thread the startWatching method because it takes forever to set up, especially with complex directory trees, so I would advise threading it as to not bind up the UI thread.