Iteration through the Android File System in the phimpme project

Android uses the single file system structure which has a single root. The task involved creating a custom folder chooser to whitelist folders while displaying images in the gallery in the Phimpme Photo App. The challenge arose in iterating over the files in the most efficient way. The best possible way to represent the file structure is in the form of tree data structure as given below.

Current Alternative

Currently, the MediaStore class contains metadata for all available media on both internal and external storage devices. Since it only returns a list of a particular media file format, it refrains the developer from customizing the structure in his way.


Create a public class which represents the file tree. Since each subtree of the tree could itself be represented as file tree itself, therefore the parent of a node will be a FileTree object itself. Therefore declare a list of FileTree objects as children of the node, a FileTree object as the parent of the particular node, node’s own File object along with string values filepath and display name associated with it.

public class FileTree {
 public final String filepath;
 public final String displayName;
 public final List<FileTree> childFileTreeList = new ArrayList<>();
 public final FileTree parent;
 public boolean hasMedia = false;

 public FileTree(String filepath, String displayName, FileTree parent) {
    this.filepath = filepath;
    this.displayName = displayName;
    this.parent = parent;

For iterating through the file system, we create a recursive function which is called on the root of the Android file system. If the particular file is a directory, with the help of Depth First traversal algorithm, the directory is traversed. Else, the file is added to the list of the file. The below code snippet is the recursive function.

public static void walkDir(FileTree fileTree, List<File> files) {
  File listFile[] = fileTree.file.listFiles();

  if (listFile != null) {
      for (File file : listFile) {
          if (file.isDirectory()) {
              FileTree childFileTree = new FileTree(file, file.getName(), fileTree);
              walkDir(childFileTree, files);
          else {



The android file system was used to whitelist folders so that the images of the folders could neither be uploaded nor edited.

For the complete guide to whitelisting folders, navigate here