Change Downloads to show individual files in the Deletion Helper.

The first implementation simply had every file in the Downloads folder
be under a single checkbox. This iteration makes Downloads an
expandable dropdown preference listing every single file individually
for selection to be deleted.

Bug: 28621781
Change-Id: I5169caf718cee4c0fa7f0248bc4c443984766005

src/com/android/settings/deletionhelper/DownloadsFilePreference.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.deletionhelper;
+
+import android.content.Context;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.CheckBoxPreference;
+import android.text.format.DateUtils;
+import android.text.format.Formatter;
+import com.android.settings.R;
+
+import java.io.File;
+
+/**
+ * DownloadsFilePreference is a preference representing a file in the Downloads folder
+ * with a checkbox that represents if the file should be deleted.
+ */
+public class DownloadsFilePreference extends CheckBoxPreference {
+    private File mFile;
+
+    public DownloadsFilePreference(Context context, File file) {
+        super(context);
+        mFile = file;
+        setKey(mFile.getPath());
+        setTitle(file.getName());
+        setSummary(context.getString(R.string.deletion_helper_downloads_summary,
+                Formatter.formatFileSize(getContext(), file.length()),
+                DateUtils.getRelativeTimeSpanString(mFile.lastModified(),
+                        System.currentTimeMillis(),
+                        DateUtils.DAY_IN_MILLIS,
+                        DateUtils.FORMAT_ABBREV_RELATIVE)));
+    }
+
+    public File getFile() {
+        return mFile;
+    }
+
+    @Override
+    public int compareTo(Preference other) {
+        if (other == null) {
+            return 1;
+        }
+
+        if (other instanceof DownloadsFilePreference) {
+            DownloadsFilePreference preference = (DownloadsFilePreference) other;
+            return Long.compare(getFile().length(), preference.getFile().length());
+        } else {
+            // If a non-DownloadsFilePreference appears, consider ourselves to be greater.
+            // This means if a non-DownloadsFilePreference sneaks into a DownloadsPreferenceGroup
+            // then the DownloadsFilePreference will appear higher.
+            return 1;
+        }
+    }
+}