Photo Picker Dialog: Recursively traverse the photo directories.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/FileEnumWorkerTask.java

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.photo_picker;
+
+import android.os.AsyncTask;
+import android.os.Environment;
+
+import org.chromium.base.ThreadUtils;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * A worker task to enumerate image files on disk.
+ */
+class FileEnumWorkerTask extends AsyncTask<Void, Void, List<PickerBitmap>> {
+    /**
+     * An interface to use to communicate back the results to the client.
+     */
+    public interface FilesEnumeratedCallback {
+        /**
+         * A callback to define to receive the list of all images on disk.
+         * @param files The list of images.
+         */
+        void filesEnumeratedCallback(List<PickerBitmap> files);
+    }
+
+    // The callback to use to communicate the results.
+    private FilesEnumeratedCallback mCallback;
+
+    // The filter to apply to the list.
+    private ImageFileFilter mFilter;
+
+    // The camera directory undir DCIM.
+    private static final String SAMPLE_DCIM_SOURCE_SUB_DIRECTORY = "Camera";
+
+    /**
+     * A FileEnumWorkerTask constructor.
+     * @param callback The callback to use to communicate back the results.
+     * @param filter The file filter to apply to the list.
+     */
+    public FileEnumWorkerTask(FilesEnumeratedCallback callback, ImageFileFilter filter) {
+        mCallback = callback;
+        mFilter = filter;
+    }
+
+    /**
+     * Retrieves the DCIM/camera directory.
+     */
+    private File getCameraDirectory() {
+        return new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM),
+                SAMPLE_DCIM_SOURCE_SUB_DIRECTORY);

[Theresa, 2017/04/11 15:44:49]

Instead of explicitly finding "Camera", can we search the entire
Environment.DIRECTORY_DCIM directory in case the folder is something like
"camera" or "Cámara". I don't think it's safe to assume that the folder name
will be in English. 

[Finnur, 2017/04/11 16:25:23]

I actually modeled this after what Google Photos does. I tried to use
DIRECTORY_DCIM instead (the parent directory) but got a lot of junk photos doing
that. If it is OK with you I'd like to add a TODO and see what the resolution is
on the discussion thread.

[Theresa, 2017/04/11 17:01:28]

Acknowledged.

+    }
+
+    /**
+     * Recursively enumerate files in a directory (and subdirectories) and add them to a list.
+     * @param directory The parent directory to recursively traverse.
+     * @param pickerBitmaps The list to add the results to.
+     * @return True if traversing can continue, false if traversing was aborted and should stop.
+     */
+    private boolean traverseDir(File directory, List<PickerBitmap> pickerBitmaps) {
+        File[] files = directory.listFiles(mFilter);
+        if (files == null) return true;
+
+        for (File file : files) {
+            if (isCancelled()) return false;
+
+            if (file.isDirectory()) {
+                if (!traverseDir(file, pickerBitmaps)) return false;

[Theresa, 2017/04/11 15:44:49]

optional nit: I liked the old

return traverseDir(file, pickerBitmaps);


but the logic is the same so it's your choice.

[Finnur, 2017/04/11 16:25:23]

I see you fell into the same mind trap I did. The logic isn't the same because
the for loop isn't supposed to end when traverseDir returns true (it is supposed
to continue with the next file).

[Theresa, 2017/04/11 17:01:28]

Ah, I see. Thank you for the explanation.

+            } else {
+                pickerBitmaps.add(new PickerBitmap(
+                        file.getPath(), file.lastModified(), PickerBitmap.PICTURE));
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Enumerates (in the background) the image files on disk. Called on a non-UI thread
+     * @param params Ignored, do not use.
+     * @return A sorted list of images (by last-modified first).
+     */
+    @Override
+    protected List<PickerBitmap> doInBackground(Void... params) {
+        assert !ThreadUtils.runningOnUiThread();
+
+        if (isCancelled()) return null;
+
+        List<PickerBitmap> pickerBitmaps = new ArrayList<>();
+
+        File[] sourceDirs = new File[] {
+                getCameraDirectory(),
+                Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
+                Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS),
+        };
+
+        for (File directory : sourceDirs) {
+            if (!traverseDir(directory, pickerBitmaps)) return null;
+        }
+
+        Collections.sort(pickerBitmaps);
+
+        pickerBitmaps.add(0, new PickerBitmap("", 0, PickerBitmap.GALLERY));
+        pickerBitmaps.add(0, new PickerBitmap("", 0, PickerBitmap.CAMERA));
+
+        return pickerBitmaps;
+    }
+
+    /**
+     * Communicates the results back to the client. Called on the UI thread.
+     * @param files The resulting list of files on disk.
+     */
+    @Override
+    protected void onPostExecute(List<PickerBitmap> files) {
+        if (isCancelled()) {
+            return;
+        }
+
+        mCallback.filesEnumeratedCallback(files);
+    }
+}