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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 
     18 package com.android.mail.providers;
     19 
     20 import com.android.mail.ui.FolderController;
     21 import com.android.mail.utils.LogTag;
     22 import com.android.mail.utils.LogUtils;
     23 
     24 import android.database.DataSetObserver;
     25 
     26 /**
     27  * A simple extension of {@link android.database.DataSetObserver} to provide the updated Folder in
     28  * {@link #onChanged(Folder)} when the Folder changes. Initializing the object registers with
     29  * the observer with the {@link com.android.mail.ui.FolderController} provided. The object will then begin to
     30  * receive {@link #onChanged(Folder)} till {@link #unregisterAndDestroy()} is called.
     31  * <p>
     32  * To implement an {@link FolderObserver}, you need to implement the {@link #onChanged(Folder)}
     33  * method.
     34  */
     35 public abstract class FolderObserver extends DataSetObserver {
     36     /**
     37      * The FolderController that the observer is registered with.
     38      */
     39     private FolderController mController;
     40 
     41     private static final String LOG_TAG = LogTag.getLogTag();
     42 
     43     /**
     44      * The no-argument constructor leaves the object unusable till
     45      * {@link #initialize(FolderController)} is called.
     46      */
     47     public FolderObserver () {
     48     }
     49 
     50     /**
     51      * Initializes an {@link FolderObserver} object that receives a call to
     52      * {@link #onChanged(Folder)} when the controller changes the Folder.
     53      *
     54      * @param controller
     55      */
     56     public Folder initialize(FolderController controller) {
     57         if (controller == null) {
     58             LogUtils.wtf(LOG_TAG, "FolderObserver initialized with null controller!");
     59         }
     60         mController = controller;
     61         mController.registerFolderObserver(this);
     62         return mController.getFolder();
     63     }
     64 
     65     @Override
     66     public final void onChanged() {
     67         if (mController == null) {
     68             return;
     69         }
     70         onChanged(mController.getFolder());
     71     }
     72 
     73     /**
     74      * Callback invoked when the Folder object is changed.  Since {@link Folder} objects are
     75      * immutable, updates can be received on changes to individual settings (sync on/off)
     76      * in addition to changes of Folders: alice (at) example.com -> bob (at) example.com.
     77      * The updated Folder is passed as the argument.
     78      * @param newFolder
     79      */
     80     public abstract void onChanged(Folder newFolder);
     81 
     82     /**
     83      * Return the current folder.
     84      * @return
     85      */
     86     public final Folder getFolder() {
     87         if (mController == null) {
     88             return null;
     89         }
     90         return mController.getFolder();
     91     }
     92 
     93     /**
     94      * Unregisters for Folder changes and makes the object unusable.
     95      */
     96     public void unregisterAndDestroy() {
     97         if (mController == null) {
     98             return;
     99         }
    100         mController.unregisterFolderObserver(this);
    101     }
    102 }
    103