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      1 /*
      2  * Copyright (C) 2012 Google Inc.
      3  * Licensed to The Android Open Source Project.
      4  *
      5  * Licensed under the Apache License, Version 2.0 (the "License");
      6  * you may not use this file except in compliance with the License.
      7  * You may obtain a copy of the License at
      8  *
      9  *      http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  * Unless required by applicable law or agreed to in writing, software
     12  * distributed under the License is distributed on an "AS IS" BASIS,
     13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  * See the License for the specific language governing permissions and
     15  * limitations under the License.
     16  */
     17 
     18 package com.android.mail.providers;
     19 
     20 import android.database.DataSetObserver;
     21 
     22 import com.android.mail.ui.RecentFolderController;
     23 import com.android.mail.ui.RecentFolderList;
     24 import com.android.mail.utils.LogTag;
     25 import com.android.mail.utils.LogUtils;
     26 
     27 /**
     28  * A simple extension of {@link DataSetObserver} to provide the updated recent folders
     29  * {@link #onChanged()} when they change. Initializing the object registers with
     30  * the observer with the {@link RecentFolderObserver} provided. The object will then begin to
     31  * receive {@link #onChanged()} till {@link #unregisterAndDestroy()} is called.
     32  * The {@link RecentFolderList} returned in {@link #initialize(RecentFolderController)} is updated
     33  * directly, no new object is created when the recent folder list is updated.
     34  * <p>
     35  * To implement an {@link RecentFolderObserver}, you need to implement the
     36  * {@link #onChanged()} method.
     37  */
     38 public abstract class RecentFolderObserver extends DataSetObserver {
     39     /**
     40      * The RecentFolderController that the observer is registered with.
     41      */
     42     private RecentFolderController mController;
     43 
     44     private static final String LOG_TAG = LogTag.getLogTag();
     45 
     46     /**
     47      * The no-argument constructor leaves the object unusable till
     48      * {@link #initialize(RecentFolderController)} is called.
     49      */
     50     public RecentFolderObserver () {
     51     }
     52 
     53     /**
     54      * Initializes an {@link RecentFolderObserver} object that receives a call to
     55      * {@link #onChanged()} when the controller changes the recent folder.
     56      *
     57      * @param controller
     58      */
     59     public RecentFolderList initialize(RecentFolderController controller) {
     60         if (controller == null) {
     61             LogUtils.wtf(LOG_TAG, "RecentFolderObserver initialized with null controller!");
     62         }
     63         mController = controller;
     64         mController.registerRecentFolderObserver(this);
     65         return mController.getRecentFolders();
     66     }
     67 
     68     @Override
     69     public abstract void onChanged();
     70 
     71     /**
     72      * Return the most current recent folder.
     73      * @return
     74      */
     75     public final RecentFolderList getRecentFolders() {
     76         if (mController == null) {
     77             return null;
     78         }
     79         return mController.getRecentFolders();
     80     }
     81 
     82     /**
     83      * Unregisters for recent folder changes and makes the object unusable.
     84      */
     85     public void unregisterAndDestroy() {
     86         if (mController == null) {
     87             return;
     88         }
     89         mController.unregisterRecentFolderObserver(this);
     90     }
     91 }