How to recursively scan directories in Android

Question

How can I recursively scan directories in Android and display file name(s)? I'm trying to scan, but it's slow (force close or wait). I'm using the FileWalker class given in a separate answer to this question.

score 20 · Accepted Answer · edited Dec 29 '22 at 22:30

20

You should almost always access the file system only from a non-UI thread. Otherwise you risk blocking the UI thread for long periods and getting an ANR. Run the FileWalker in an AsyncTask's doInBackground().

This is a slightly optimized version of FileWalker:

public class Filewalker {

    public void walk(File root) {

        File[] list = root.listFiles();

        for (File f : list) {
            if (f.isDirectory()) {
                Log.d("", "Dir: " + f.getAbsoluteFile());
                walk(f);
            }
            else {
                Log.d("", "File: " + f.getAbsoluteFile());
            }
        }
    }
}

You can invoke it from a background thread like this:

Filewalker fw = new Filewalker();
fw.walk(context.getFilesDir());

edited Dec 29 '22 at 22:30

Peter Mortensen

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answered Jul 14 '12 at 08:50

Dheeraj Vepakomma

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Forgive my naive question but how is context being assigned here? I typically pass it through from an activity as an argument to a function but I see no arguments here? Without, context is giving me a 'cannot resolve' compile error. – biscuitstack Jul 11 '16 at 11:19
1

@biscuitstack You can use an instance of an `Activity` or `Application` as the [`Context`](https://developer.android.com/reference/android/content/Context.html). – Dheeraj Vepakomma Jul 11 '16 at 13:18
This will need some more reading but you've given me a direction to go in, thanks Dheeraj. – biscuitstack Jul 11 '16 at 13:21

score 0 · Answer 2 · answered Jul 14 '12 at 08:40

System.out.println calls are really slow (well it's not really the function itself, but the underlying PrintStream which takes a lot of time to write text in the console).

Replace them by something else and it should be fine. For example, you can create and return an array with the file names.

score 0 · Answer 3 · edited Jun 18 '23 at 18:29

If you prefer a non-recursive method you could try something like:

public void filetree (File directory)
{
    List<File> dirlist = new ArrayList<File>();  // The list of directories to scan
    dirlist.add(directory);     // Initialize - with the stating point
    do {            // The scan list cannot start with zero entries - so bottom exit
        File f = dirlist.remove(0);     // Extract the directory to scan
        if (f.listFiles() != null)      // Check for permissions problems
            for (File fl : f.listFiles())
                if (fl.isDirectory()) dirlist.add(fl.getAbsoluteFile());    // directory - add to list
                else Log.i ("msg", "File: " + fl.getAbsoluteFile());  // File - do something with it
    } while (!dirlist.isEmpty());  // Continue until there is nothing left to scan
}

Where did you copy that from? – Peter Mortensen Jun 18 '23 at 18:30 — Peter Mortensen, Jun 18 '23 at 18:30

How to recursively scan directories in Android

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