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      1 /*
      2  * Copyright (C) 2015 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 package com.android.tv.settings.util;
     18 
     19 import android.content.AsyncTaskLoader;
     20 import android.content.Context;
     21 
     22 /**
     23  * This class fills in some boilerplate for AsyncTaskLoader to actually load things.
     24  *
     25  * Subclasses need to implement {@link SettingsAsyncTaskLoader#loadInBackground()} to perform the
     26  * actual background task, and {@link SettingsAsyncTaskLoader#onDiscardResult(T)} to clean up
     27  * previously loaded results.
     28  */
     29 
     30 public abstract class SettingsAsyncTaskLoader<T> extends AsyncTaskLoader<T> {
     31     private T mResult;
     32 
     33     public SettingsAsyncTaskLoader(final Context context) {
     34         super(context);
     35     }
     36 
     37     @Override
     38     protected void onStartLoading() {
     39         if (mResult != null) {
     40             deliverResult(mResult);
     41         }
     42 
     43         if (takeContentChanged() || mResult == null) {
     44             forceLoad();
     45         }
     46     }
     47 
     48     @Override
     49     protected void onStopLoading() {
     50         cancelLoad();
     51     }
     52 
     53     @Override
     54     public void deliverResult(final T data) {
     55         if (isReset()) {
     56             if (data != null) {
     57                 onDiscardResult(data);
     58             }
     59             return;
     60         }
     61 
     62         final T oldResult = mResult;
     63         mResult = data;
     64 
     65         if (isStarted()) {
     66             super.deliverResult(data);
     67         }
     68 
     69         if (oldResult != null && oldResult != mResult) {
     70             onDiscardResult(oldResult);
     71         }
     72     }
     73 
     74     @Override
     75     protected void onReset() {
     76         super.onReset();
     77 
     78         onStopLoading();
     79 
     80         if (mResult != null) {
     81             onDiscardResult(mResult);
     82         }
     83         mResult = null;
     84     }
     85 
     86     @Override
     87     public void onCanceled(final T data) {
     88         super.onCanceled(data);
     89 
     90         if (data != null) {
     91             onDiscardResult(data);
     92         }
     93     }
     94 
     95     /**
     96      * Called when discarding the load results so subclasses can take care of clean-up or
     97      * recycling tasks. This is not called if the same result (by way of pointer equality) is
     98      * returned again by a subsequent call to loadInBackground, or if result is null.
     99      *
    100      * Note that this may be called concurrently with loadInBackground(), and in some circumstances
    101      * may be called more than once for a given object.
    102      *
    103      * @param result The value returned from {@link SettingsAsyncTaskLoader#loadInBackground()} which
    104      *               is to be discarded.
    105      */
    106     protected abstract void onDiscardResult(final T result);
    107 }
    108