Question

I want to know when a file is finished writing, and to do that I’m trying to use FileObserver. I’m doing it like this:

FileObserver observer = new FileObserver(imageUri.getPath()) {
        @Override
        public void onEvent(int event, String path) {
            if(event == FileObserver.CLOSE_WRITE)
                Log.d(TAG, "FILE: "+path);
        }
};
observer.startWatching();

imageUri is a valid Uri. When the file is closed I get the following log entry:

FILE: null

Why is it null? It’s possible that the user writes several files, so I need to know which one is triggering the event.

Thanks!

Answer 1

According to the documentation of onEvent():

The path, relative to the main monitored file or directory, of the file or directory which triggered the event

So I guess when path is null it is the the specified file or directory…

You need to keep track of the original path yourself. And append the path of onEvent() to this path to get the full path (unless you are tracking a file and its value is always null):

FileObserver observer = new FileObserver(imageUri.getPath()) {
    public String basePath;

    @Override
    public void onEvent(int event, String path) {
        String fullPath = basePath;
        if(path != null) {
            // Eventually add a '/' in between (depending on basePath)
            fullPath += path;
        }
        Log.d(TAG, "FILE: "+fullPath);
    }
};
observer.basePath = imageUri.getPath();
observer.startWatching();

I tried to keep the example as close to your code snippet as possible. But, it is much better to create a full-blown class extending FileObserver, so you can add an constructor to store the basePath and are not required to access the public field from outside the class/instance!