Sort array of DocumentFiles faster in Android

Question

In this case I have to sort hundreds of DocumentFile objects using this method:

                DocumentFile[] files = documentFile.listFiles();
                ArrayList<DocumentFile> docFiles = new ArrayList<DocumentFile>();

                Arrays.sort(files, new Comparator() {
                    public int compare(Object o1, Object o2) {

                        if (((DocumentFile)o1).lastModified() < ((DocumentFile)o2).lastModified()) {
                            return -1;
                        } else if (((DocumentFile)o1).lastModified() > ((DocumentFile)o2).lastModified()) {
                            return +1;
                        } else {
                            return 0;
                        }
                    }

                });

                if (files != null) {
                    for (DocumentFile file : files) {

                        if (!docFiles.contains(file))
                            docFiles.add(file);



                    }

However, this takes way too long, about a MINUTE with 200 DocumentFile objects. I cannot understand this kind of vital class is so slow. It will have to be used more with the recent scoped storage changes.

Anyone have an idea how to get this sorting process done faster?

Every `lastModified()` call involves IPC to a `ContentProvider`. `DocumentFile` does not cache this sort of data (in part because it could change). Create yourself a `DocumentFileEntry` class (or whatever) that holds the `DocumentFile` and its last-modified timestamp. Build up a list of those, filling in the last-modified timestamp with the value of `lastModified()`. Then, sort the `DocumentFileEntry` list, so you work off of those cached timestamps. — CommonsWare, Aug 17 '20 at 21:34
If you want speed then do not use DocumentFile to list the content of directories to begin with. Use DocumentsContract instead. It can be up to twenty times faster. — blackapps, Aug 17 '20 at 21:50

score 0 · Accepted Answer · answered Aug 18 '20 at 10:46

Many — perhaps most — of the methods on DocumentFile wind up making requests of a ContentProvider. Such requests are not cheap. And lastModified() is such a method. Sorting 200 objects will result in thousands of these calls, and that is why it is taking a long time.

What you can do is:

Create a wrapper for DocumentFile that holds the DocumentFile plus a cached copy of lastModified()
Create a list of those from your list of DocumentFile objects, so you make one lastModified() call per DocumentFile
Sort the list of wrappers, using the cached lastModified() value in the Comparator

Making 200 lastModified() calls is not going to be fast, but it will be faster than making thousands of those calls.

Extends is not possible, because `DocumentFile` constructor is package-private. https://issuetracker.google.com/issues/179709049 — t0m, May 06 '21 at 06:38
@t0m: I suggested creating a wrapper, not creating a subclass. — CommonsWare, May 06 '21 at 11:09

Sort array of DocumentFiles faster in Android

1 Answers1