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      1 /*
      2  * Copyright (C) 2017 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.settingslib.utils;
     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 AsyncLoader#loadInBackground()} to perform the actual
     26  * background task, and {@link AsyncLoader#onDiscardResult(T)} to clean up previously loaded
     27  * results.
     28  *
     29  * This loader is based on the MailAsyncTaskLoader from the AOSP EmailUnified repo.
     30  *
     31  * @param <T> the data type to be loaded.
     32  */
     33 public abstract class AsyncLoader<T> extends AsyncTaskLoader<T> {
     34     private T mResult;
     35 
     36     public AsyncLoader(final Context context) {
     37         super(context);
     38     }
     39 
     40     @Override
     41     protected void onStartLoading() {
     42         if (mResult != null) {
     43             deliverResult(mResult);
     44         }
     45 
     46         if (takeContentChanged() || mResult == null) {
     47             forceLoad();
     48         }
     49     }
     50 
     51     @Override
     52     protected void onStopLoading() {
     53         cancelLoad();
     54     }
     55 
     56     @Override
     57     public void deliverResult(final T data) {
     58         if (isReset()) {
     59             if (data != null) {
     60                 onDiscardResult(data);
     61             }
     62             return;
     63         }
     64 
     65         final T oldResult = mResult;
     66         mResult = data;
     67 
     68         if (isStarted()) {
     69             super.deliverResult(data);
     70         }
     71 
     72         if (oldResult != null && oldResult != mResult) {
     73             onDiscardResult(oldResult);
     74         }
     75     }
     76 
     77     @Override
     78     protected void onReset() {
     79         super.onReset();
     80 
     81         onStopLoading();
     82 
     83         if (mResult != null) {
     84             onDiscardResult(mResult);
     85         }
     86         mResult = null;
     87     }
     88 
     89     @Override
     90     public void onCanceled(final T data) {
     91         super.onCanceled(data);
     92 
     93         if (data != null) {
     94             onDiscardResult(data);
     95         }
     96     }
     97 
     98     /**
     99      * Called when discarding the load results so subclasses can take care of clean-up or
    100      * recycling tasks. This is not called if the same result (by way of pointer equality) is
    101      * returned again by a subsequent call to loadInBackground, or if result is null.
    102      *
    103      * Note that this may be called concurrently with loadInBackground(), and in some circumstances
    104      * may be called more than once for a given object.
    105      *
    106      * @param result The value returned from {@link AsyncLoader#loadInBackground()} which
    107      *               is to be discarded.
    108      */
    109     protected abstract void onDiscardResult(T result);
    110 }
    111