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      1 /*
      2  * Copyright (C) 2016 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 package com.android.contacts.util.concurrent;
     17 
     18 import android.content.BroadcastReceiver;
     19 import android.content.Context;
     20 import android.content.Intent;
     21 import android.content.IntentFilter;
     22 import android.content.Loader;
     23 import android.support.v4.content.LocalBroadcastManager;
     24 import android.util.Log;
     25 
     26 import com.google.common.util.concurrent.FutureCallback;
     27 import com.google.common.util.concurrent.Futures;
     28 import com.google.common.util.concurrent.ListenableFuture;
     29 
     30 import java.util.concurrent.CancellationException;
     31 import java.util.concurrent.Executor;
     32 
     33 /**
     34  * Wraps a ListenableFuture for integration with {@link android.app.LoaderManager}
     35  *
     36  * <p>Using a loader ensures that the result is delivered while the receiving component (activity
     37  * or fragment) is resumed and also prevents leaking references these components
     38  * </p>
     39  */
     40 public abstract class ListenableFutureLoader<D> extends Loader<D> {
     41     private static final String TAG = "FutureLoader";
     42 
     43     private final IntentFilter mReloadFilter;
     44     private final Executor mUiExecutor;
     45     private final LocalBroadcastManager mLocalBroadcastManager;
     46 
     47     private ListenableFuture<D> mFuture;
     48     private D mLoadedData;
     49 
     50     private BroadcastReceiver mReceiver;
     51 
     52     /**
     53      * Stores away the application context associated with context.
     54      * Since Loaders can be used across multiple activities it's dangerous to
     55      * store the context directly; always use {@link #getContext()} to retrieve
     56      * the Loader's Context, don't use the constructor argument directly.
     57      * The Context returned by {@link #getContext} is safe to use across
     58      * Activity instances.
     59      *
     60      * @param context used to retrieve the application context.
     61      */
     62     public ListenableFutureLoader(Context context) {
     63         this(context, null);
     64     }
     65 
     66     public ListenableFutureLoader(Context context, IntentFilter reloadBroadcastFilter) {
     67         super(context);
     68         mUiExecutor = ContactsExecutors.newUiThreadExecutor();
     69         mReloadFilter = reloadBroadcastFilter;
     70         mLocalBroadcastManager = LocalBroadcastManager.getInstance(context);
     71     }
     72 
     73     @Override
     74     protected void onStartLoading() {
     75         if (mReloadFilter != null && mReceiver == null) {
     76             mReceiver = new ForceLoadReceiver();
     77             mLocalBroadcastManager.registerReceiver(mReceiver, mReloadFilter);
     78         }
     79 
     80         if (mLoadedData != null) {
     81             deliverResult(mLoadedData);
     82         }
     83         if (mFuture == null) {
     84             takeContentChanged();
     85             forceLoad();
     86         } else if (takeContentChanged()) {
     87             forceLoad();
     88         }
     89     }
     90 
     91     @Override
     92     protected void onForceLoad() {
     93         mFuture = loadData();
     94         Futures.addCallback(mFuture, new FutureCallback<D>() {
     95             @Override
     96             public void onSuccess(D result) {
     97                 if (mLoadedData == null || !isSameData(mLoadedData, result)) {
     98                     deliverResult(result);
     99                 }
    100                 mLoadedData = result;
    101                 commitContentChanged();
    102             }
    103 
    104             @Override
    105             public void onFailure(Throwable t) {
    106                 if (t instanceof CancellationException) {
    107                     Log.i(TAG, "Loading cancelled", t);
    108                     rollbackContentChanged();
    109                 } else {
    110                     Log.e(TAG, "Loading failed", t);
    111                 }
    112             }
    113         }, mUiExecutor);
    114     }
    115 
    116     @Override
    117     protected void onStopLoading() {
    118         if (mFuture != null) {
    119             mFuture.cancel(false);
    120             mFuture = null;
    121         }
    122     }
    123 
    124     @Override
    125     protected void onReset() {
    126         mFuture = null;
    127         mLoadedData = null;
    128         if (mReceiver != null) {
    129             mLocalBroadcastManager.unregisterReceiver(mReceiver);
    130         }
    131     }
    132 
    133     protected abstract ListenableFuture<D> loadData();
    134 
    135     /**
    136      * Returns whether the newly loaded data is the same as the cached value
    137      *
    138      * <p>This allows subclasses to suppress delivering results when the data hasn't
    139      * actually changed. By default it will always return false.
    140      * </p>
    141      */
    142     protected boolean isSameData(D previousData, D newData) {
    143         return false;
    144     }
    145 
    146     public final D getLoadedData() {
    147         return mLoadedData;
    148     }
    149 
    150     public class ForceLoadReceiver extends BroadcastReceiver {
    151         @Override
    152         public void onReceive(Context context, Intent intent) {
    153             onContentChanged();
    154         }
    155     }
    156 }
    157