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/*
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* Copyright (C) 2008 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.example.android.displayingbitmaps.util;
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import android.annotation.TargetApi;
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import android.os.Handler;
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import android.os.Message;
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import android.os.Process;
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import java.util.ArrayDeque;
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import java.util.concurrent.BlockingQueue;
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import java.util.concurrent.Callable;
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import java.util.concurrent.CancellationException;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.Executor;
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import java.util.concurrent.Executors;
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import java.util.concurrent.FutureTask;
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import java.util.concurrent.LinkedBlockingQueue;
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import java.util.concurrent.ThreadFactory;
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import java.util.concurrent.ThreadPoolExecutor;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.TimeoutException;
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import java.util.concurrent.atomic.AtomicBoolean;
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import java.util.concurrent.atomic.AtomicInteger;
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/**
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* *************************************
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* Copied from JB release framework:
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* https://android.googlesource.com/platform/frameworks/base/+/jb-release/core/java/android/os/AsyncTask.java
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*
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* so that threading behavior on all OS versions is the same and we can tweak behavior by using
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* executeOnExecutor() if needed.
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*
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* There are 3 changes in this copy of AsyncTask:
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* -pre-HC a single thread executor is used for serial operation
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* (Executors.newSingleThreadExecutor) and is the default
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* -the default THREAD_POOL_EXECUTOR was changed to use DiscardOldestPolicy
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* -a new fixed thread pool called DUAL_THREAD_EXECUTOR was added
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* *************************************
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*
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* <p>AsyncTask enables proper and easy use of the UI thread. This class allows to
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* perform background operations and publish results on the UI thread without
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* having to manipulate threads and/or handlers.</p>
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*
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* <p>AsyncTask is designed to be a helper class around {@link Thread} and {@link android.os.Handler}
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* and does not constitute a generic threading framework. AsyncTasks should ideally be
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* used for short operations (a few seconds at the most.) If you need to keep threads
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* running for long periods of time, it is highly recommended you use the various APIs
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* provided by the <code>java.util.concurrent</code> pacakge such as {@link java.util.concurrent.Executor},
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* {@link java.util.concurrent.ThreadPoolExecutor} and {@link java.util.concurrent.FutureTask}.</p>
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*
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* <p>An asynchronous task is defined by a computation that runs on a background thread and
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* whose result is published on the UI thread. An asynchronous task is defined by 3 generic
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* types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
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* and 4 steps, called <code>onPreExecute</code>, <code>doInBackground</code>,
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* <code>onProgressUpdate</code> and <code>onPostExecute</code>.</p>
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*
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* <div class="special reference">
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* <h3>Developer Guides</h3>
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* <p>For more information about using tasks and threads, read the
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* <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html">Processes and
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* Threads</a> developer guide.</p>
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* </div>
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*
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* <h2>Usage</h2>
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* <p>AsyncTask must be subclassed to be used. The subclass will override at least
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* one method ({@link #doInBackground}), and most often will override a
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* second one ({@link #onPostExecute}.)</p>
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*
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* <p>Here is an example of subclassing:</p>
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* <pre class="prettyprint">
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* private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
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* protected Long doInBackground(URL... urls) {
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* int count = urls.length;
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* long totalSize = 0;
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* for (int i = 0; i < count; i++) {
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* totalSize += Downloader.downloadFile(urls[i]);
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* publishProgress((int) ((i / (float) count) * 100));
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* // Escape early if cancel() is called
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* if (isCancelled()) break;
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* }
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* return totalSize;
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* }
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*
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* protected void onProgressUpdate(Integer... progress) {
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* setProgressPercent(progress[0]);
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* }
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*
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* protected void onPostExecute(Long result) {
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* showDialog("Downloaded " + result + " bytes");
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* }
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* }
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* </pre>
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*
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* <p>Once created, a task is executed very simply:</p>
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* <pre class="prettyprint">
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* new DownloadFilesTask().execute(url1, url2, url3);
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* </pre>
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*
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* <h2>AsyncTask's generic types</h2>
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* <p>The three types used by an asynchronous task are the following:</p>
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* <ol>
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* <li><code>Params</code>, the type of the parameters sent to the task upon
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* execution.</li>
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* <li><code>Progress</code>, the type of the progress units published during
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* the background computation.</li>
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* <li><code>Result</code>, the type of the result of the background
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* computation.</li>
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* </ol>
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* <p>Not all types are always used by an asynchronous task. To mark a type as unused,
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* simply use the type {@link Void}:</p>
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* <pre>
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* private class MyTask extends AsyncTask<Void, Void, Void> { ... }
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* </pre>
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*
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* <h2>The 4 steps</h2>
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* <p>When an asynchronous task is executed, the task goes through 4 steps:</p>
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* <ol>
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* <li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
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* is executed. This step is normally used to setup the task, for instance by
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* showing a progress bar in the user interface.</li>
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* <li>{@link #doInBackground}, invoked on the background thread
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* immediately after {@link #onPreExecute()} finishes executing. This step is used
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* to perform background computation that can take a long time. The parameters
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* of the asynchronous task are passed to this step. The result of the computation must
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* be returned by this step and will be passed back to the last step. This step
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* can also use {@link #publishProgress} to publish one or more units
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* of progress. These values are published on the UI thread, in the
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* {@link #onProgressUpdate} step.</li>
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* <li>{@link #onProgressUpdate}, invoked on the UI thread after a
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* call to {@link #publishProgress}. The timing of the execution is
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* undefined. This method is used to display any form of progress in the user
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* interface while the background computation is still executing. For instance,
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* it can be used to animate a progress bar or show logs in a text field.</li>
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* <li>{@link #onPostExecute}, invoked on the UI thread after the background
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* computation finishes. The result of the background computation is passed to
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* this step as a parameter.</li>
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* </ol>
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*
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* <h2>Cancelling a task</h2>
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* <p>A task can be cancelled at any time by invoking {@link #cancel(boolean)}. Invoking
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* this method will cause subsequent calls to {@link #isCancelled()} to return true.
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* After invoking this method, {@link #onCancelled(Object)}, instead of
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* {@link #onPostExecute(Object)} will be invoked after {@link #doInBackground(Object[])}
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* returns. To ensure that a task is cancelled as quickly as possible, you should always
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* check the return value of {@link #isCancelled()} periodically from
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* {@link #doInBackground(Object[])}, if possible (inside a loop for instance.)</p>
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*
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* <h2>Threading rules</h2>
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* <p>There are a few threading rules that must be followed for this class to
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* work properly:</p>
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* <ul>
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* <li>The AsyncTask class must be loaded on the UI thread. This is done
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* automatically as of {@link android.os.Build.VERSION_CODES#JELLY_BEAN}.</li>
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* <li>The task instance must be created on the UI thread.</li>
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* <li>{@link #execute} must be invoked on the UI thread.</li>
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* <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
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* {@link #doInBackground}, {@link #onProgressUpdate} manually.</li>
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* <li>The task can be executed only once (an exception will be thrown if
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* a second execution is attempted.)</li>
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* </ul>
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*
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* <h2>Memory observability</h2>
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* <p>AsyncTask guarantees that all callback calls are synchronized in such a way that the following
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* operations are safe without explicit synchronizations.</p>
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* <ul>
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* <li>Set member fields in the constructor or {@link #onPreExecute}, and refer to them
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* in {@link #doInBackground}.
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* <li>Set member fields in {@link #doInBackground}, and refer to them in
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* {@link #onProgressUpdate} and {@link #onPostExecute}.
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* </ul>
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*
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* <h2>Order of execution</h2>
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* <p>When first introduced, AsyncTasks were executed serially on a single background
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* thread. Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
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* to a pool of threads allowing multiple tasks to operate in parallel. Starting with
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* {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are executed on a single
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* thread to avoid common application errors caused by parallel execution.</p>
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* <p>If you truly want parallel execution, you can invoke
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* {@link #executeOnExecutor(java.util.concurrent.Executor, Object[])} with
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* {@link #THREAD_POOL_EXECUTOR}.</p>
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*/
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public abstract class AsyncTask<Params, Progress, Result> {
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private static final String LOG_TAG = "AsyncTask";
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private static final int CORE_POOL_SIZE = 5;
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private static final int MAXIMUM_POOL_SIZE = 128;
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private static final int KEEP_ALIVE = 1;
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private static final ThreadFactory sThreadFactory = new ThreadFactory() {
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private final AtomicInteger mCount = new AtomicInteger(1);
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public Thread newThread(Runnable r) {
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return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
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}
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};
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private static final BlockingQueue<Runnable> sPoolWorkQueue =
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new LinkedBlockingQueue<Runnable>(10);
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/**
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* An {@link java.util.concurrent.Executor} that can be used to execute tasks in parallel.
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*/
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public static final Executor THREAD_POOL_EXECUTOR
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= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
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TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory,
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new ThreadPoolExecutor.DiscardOldestPolicy());
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/**
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* An {@link java.util.concurrent.Executor} that executes tasks one at a time in serial
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* order. This serialization is global to a particular process.
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*/
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public static final Executor SERIAL_EXECUTOR = Utils.hasHoneycomb() ? new SerialExecutor() :
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Executors.newSingleThreadExecutor(sThreadFactory);
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public static final Executor DUAL_THREAD_EXECUTOR =
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Executors.newFixedThreadPool(2, sThreadFactory);
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private static final int MESSAGE_POST_RESULT = 0x1;
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private static final int MESSAGE_POST_PROGRESS = 0x2;
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private static final InternalHandler sHandler = new InternalHandler();
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private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
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private final WorkerRunnable<Params, Result> mWorker;
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private final FutureTask<Result> mFuture;
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private volatile Status mStatus = Status.PENDING;
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private final AtomicBoolean mCancelled = new AtomicBoolean();
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private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
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@TargetApi(11)
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private static class SerialExecutor implements Executor {
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final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
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Runnable mActive;
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public synchronized void execute(final Runnable r) {
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mTasks.offer(new Runnable() {
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public void run() {
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try {
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r.run();
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} finally {
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scheduleNext();
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}
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}
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});
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if (mActive == null) {
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scheduleNext();
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}
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}
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protected synchronized void scheduleNext() {
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if ((mActive = mTasks.poll()) != null) {
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THREAD_POOL_EXECUTOR.execute(mActive);
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}
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}
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}
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/**
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* Indicates the current status of the task. Each status will be set only once
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* during the lifetime of a task.
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*/
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public enum Status {
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/**
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* Indicates that the task has not been executed yet.
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*/
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PENDING,
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/**
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* Indicates that the task is running.
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*/
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RUNNING,
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/**
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* Indicates that {@link AsyncTask#onPostExecute} has finished.
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*/
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FINISHED,
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}
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/** @hide Used to force static handler to be created. */
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public static void init() {
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sHandler.getLooper();
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}
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/** @hide */
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public static void setDefaultExecutor(Executor exec) {
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sDefaultExecutor = exec;
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}
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/**
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* Creates a new asynchronous task. This constructor must be invoked on the UI thread.
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*/
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public AsyncTask() {
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mWorker = new WorkerRunnable<Params, Result>() {
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public Result call() throws Exception {
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mTaskInvoked.set(true);
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Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
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//noinspection unchecked
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return postResult(doInBackground(mParams));
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}
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};
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mFuture = new FutureTask<Result>(mWorker) {
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@Override
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protected void done() {
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try {
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postResultIfNotInvoked(get());
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} catch (InterruptedException e) {
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android.util.Log.w(LOG_TAG, e);
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} catch (ExecutionException e) {
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throw new RuntimeException("An error occured while executing doInBackground()",
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e.getCause());
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} catch (CancellationException e) {
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postResultIfNotInvoked(null);
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}
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}
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};
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}
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private void postResultIfNotInvoked(Result result) {
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final boolean wasTaskInvoked = mTaskInvoked.get();
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if (!wasTaskInvoked) {
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postResult(result);
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}
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}
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private Result postResult(Result result) {
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@SuppressWarnings("unchecked")
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Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
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new AsyncTaskResult<Result>(this, result));
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message.sendToTarget();
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return result;
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}
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/**
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* Returns the current status of this task.
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*
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* @return The current status.
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*/
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public final Status getStatus() {
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return mStatus;
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}
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/**
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* Override this method to perform a computation on a background thread. The
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* specified parameters are the parameters passed to {@link #execute}
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* by the caller of this task.
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*
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* This method can call {@link #publishProgress} to publish updates
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* on the UI thread.
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*
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* @param params The parameters of the task.
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*
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* @return A result, defined by the subclass of this task.
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*
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* @see #onPreExecute()
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* @see #onPostExecute
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* @see #publishProgress
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*/
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protected abstract Result doInBackground(Params... params);
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/**
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* Runs on the UI thread before {@link #doInBackground}.
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*
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* @see #onPostExecute
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* @see #doInBackground
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*/
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protected void onPreExecute() {
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}
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/**
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* <p>Runs on the UI thread after {@link #doInBackground}. The
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* specified result is the value returned by {@link #doInBackground}.</p>
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*
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* <p>This method won't be invoked if the task was cancelled.</p>
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*
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* @param result The result of the operation computed by {@link #doInBackground}.
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*
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* @see #onPreExecute
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* @see #doInBackground
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* @see #onCancelled(Object)
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*/
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@SuppressWarnings({"UnusedDeclaration"})
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protected void onPostExecute(Result result) {
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}
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/**
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* Runs on the UI thread after {@link #publishProgress} is invoked.
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* The specified values are the values passed to {@link #publishProgress}.
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*
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* @param values The values indicating progress.
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*
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* @see #publishProgress
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* @see #doInBackground
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*/
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@SuppressWarnings({"UnusedDeclaration"})
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protected void onProgressUpdate(Progress... values) {
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}
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414
/**
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* <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
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* {@link #doInBackground(Object[])} has finished.</p>
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*
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* <p>The default implementation simply invokes {@link #onCancelled()} and
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* ignores the result. If you write your own implementation, do not call
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* <code>super.onCancelled(result)</code>.</p>
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*
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* @param result The result, if any, computed in
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* {@link #doInBackground(Object[])}, can be null
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*
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* @see #cancel(boolean)
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* @see #isCancelled()
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*/
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@SuppressWarnings({"UnusedParameters"})
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protected void onCancelled(Result result) {
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onCancelled();
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}
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433
/**
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* <p>Applications should preferably override {@link #onCancelled(Object)}.
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* This method is invoked by the default implementation of
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* {@link #onCancelled(Object)}.</p>
437
*
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* <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
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* {@link #doInBackground(Object[])} has finished.</p>
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*
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* @see #onCancelled(Object)
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* @see #cancel(boolean)
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* @see #isCancelled()
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*/
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protected void onCancelled() {
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}
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448
/**
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* Returns <tt>true</tt> if this task was cancelled before it completed
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* normally. If you are calling {@link #cancel(boolean)} on the task,
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* the value returned by this method should be checked periodically from
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* {@link #doInBackground(Object[])} to end the task as soon as possible.
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*
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* @return <tt>true</tt> if task was cancelled before it completed
455
*
456
* @see #cancel(boolean)
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*/
458
public final boolean isCancelled() {
459
return mCancelled.get();
460
}
461
462
/**
463
* <p>Attempts to cancel execution of this task. This attempt will
464
* fail if the task has already completed, already been cancelled,
465
* or could not be cancelled for some other reason. If successful,
466
* and this task has not started when <tt>cancel</tt> is called,
467
* this task should never run. If the task has already started,
468
* then the <tt>mayInterruptIfRunning</tt> parameter determines
469
* whether the thread executing this task should be interrupted in
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* an attempt to stop the task.</p>
471
*
472
* <p>Calling this method will result in {@link #onCancelled(Object)} being
473
* invoked on the UI thread after {@link #doInBackground(Object[])}
474
* returns. Calling this method guarantees that {@link #onPostExecute(Object)}
475
* is never invoked. After invoking this method, you should check the
476
* value returned by {@link #isCancelled()} periodically from
477
* {@link #doInBackground(Object[])} to finish the task as early as
478
* possible.</p>
479
*
480
* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
481
* task should be interrupted; otherwise, in-progress tasks are allowed
482
* to complete.
483
*
484
* @return <tt>false</tt> if the task could not be cancelled,
485
* typically because it has already completed normally;
486
* <tt>true</tt> otherwise
487
*
488
* @see #isCancelled()
489
* @see #onCancelled(Object)
490
*/
491
public final boolean cancel(boolean mayInterruptIfRunning) {
492
mCancelled.set(true);
493
return mFuture.cancel(mayInterruptIfRunning);
494
}
495
496
/**
497
* Waits if necessary for the computation to complete, and then
498
* retrieves its result.
499
*
500
* @return The computed result.
501
*
502
* @throws java.util.concurrent.CancellationException If the computation was cancelled.
503
* @throws java.util.concurrent.ExecutionException If the computation threw an exception.
504
* @throws InterruptedException If the current thread was interrupted
505
* while waiting.
506
*/
507
public final Result get() throws InterruptedException, ExecutionException {
508
return mFuture.get();
509
}
510
511
/**
512
* Waits if necessary for at most the given time for the computation
513
* to complete, and then retrieves its result.
514
*
515
* @param timeout Time to wait before cancelling the operation.
516
* @param unit The time unit for the timeout.
517
*
518
* @return The computed result.
519
*
520
* @throws java.util.concurrent.CancellationException If the computation was cancelled.
521
* @throws java.util.concurrent.ExecutionException If the computation threw an exception.
522
* @throws InterruptedException If the current thread was interrupted
523
* while waiting.
524
* @throws java.util.concurrent.TimeoutException If the wait timed out.
525
*/
526
public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
527
ExecutionException, TimeoutException {
528
return mFuture.get(timeout, unit);
529
}
530
531
/**
532
* Executes the task with the specified parameters. The task returns
533
* itself (this) so that the caller can keep a reference to it.
534
*
535
* <p>Note: this function schedules the task on a queue for a single background
536
* thread or pool of threads depending on the platform version. When first
537
* introduced, AsyncTasks were executed serially on a single background thread.
538
* Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
539
* to a pool of threads allowing multiple tasks to operate in parallel. Starting
540
* {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are back to being
541
* executed on a single thread to avoid common application errors caused
542
* by parallel execution. If you truly want parallel execution, you can use
543
* the {@link #executeOnExecutor} version of this method
544
* with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings
545
* on its use.
546
*
547
* <p>This method must be invoked on the UI thread.
548
*
549
* @param params The parameters of the task.
550
*
551
* @return This instance of AsyncTask.
552
*
553
* @throws IllegalStateException If {@link #getStatus()} returns either
554
* {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
555
*
556
* @see #executeOnExecutor(java.util.concurrent.Executor, Object[])
557
* @see #execute(Runnable)
558
*/
559
public final AsyncTask<Params, Progress, Result> execute(Params... params) {
560
return executeOnExecutor(sDefaultExecutor, params);
561
}
562
563
/**
564
* Executes the task with the specified parameters. The task returns
565
* itself (this) so that the caller can keep a reference to it.
566
*
567
* <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to
568
* allow multiple tasks to run in parallel on a pool of threads managed by
569
* AsyncTask, however you can also use your own {@link java.util.concurrent.Executor} for custom
570
* behavior.
571
*
572
* <p><em>Warning:</em> Allowing multiple tasks to run in parallel from
573
* a thread pool is generally <em>not</em> what one wants, because the order
574
* of their operation is not defined. For example, if these tasks are used
575
* to modify any state in common (such as writing a file due to a button click),
576
* there are no guarantees on the order of the modifications.
577
* Without careful work it is possible in rare cases for the newer version
578
* of the data to be over-written by an older one, leading to obscure data
579
* loss and stability issues. Such changes are best
580
* executed in serial; to guarantee such work is serialized regardless of
581
* platform version you can use this function with {@link #SERIAL_EXECUTOR}.
582
*
583
* <p>This method must be invoked on the UI thread.
584
*
585
* @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as a
586
* convenient process-wide thread pool for tasks that are loosely coupled.
587
* @param params The parameters of the task.
588
*
589
* @return This instance of AsyncTask.
590
*
591
* @throws IllegalStateException If {@link #getStatus()} returns either
592
* {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
593
*
594
* @see #execute(Object[])
595
*/
596
public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
597
Params... params) {
598
if (mStatus != Status.PENDING) {
599
switch (mStatus) {
600
case RUNNING:
601
throw new IllegalStateException("Cannot execute task:"
602
+ " the task is already running.");
603
case FINISHED:
604
throw new IllegalStateException("Cannot execute task:"
605
+ " the task has already been executed "
606
+ "(a task can be executed only once)");
607
}
608
}
609
610
mStatus = Status.RUNNING;
611
612
onPreExecute();
613
614
mWorker.mParams = params;
615
exec.execute(mFuture);
616
617
return this;
618
}
619
620
/**
621
* Convenience version of {@link #execute(Object...)} for use with
622
* a simple Runnable object. See {@link #execute(Object[])} for more
623
* information on the order of execution.
624
*
625
* @see #execute(Object[])
626
* @see #executeOnExecutor(java.util.concurrent.Executor, Object[])
627
*/
628
public static void execute(Runnable runnable) {
629
sDefaultExecutor.execute(runnable);
630
}
631
632
/**
633
* This method can be invoked from {@link #doInBackground} to
634
* publish updates on the UI thread while the background computation is
635
* still running. Each call to this method will trigger the execution of
636
* {@link #onProgressUpdate} on the UI thread.
637
*
638
* {@link #onProgressUpdate} will note be called if the task has been
639
* canceled.
640
*
641
* @param values The progress values to update the UI with.
642
*
643
* @see #onProgressUpdate
644
* @see #doInBackground
645
*/
646
protected final void publishProgress(Progress... values) {
647
if (!isCancelled()) {
648
sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
649
new AsyncTaskResult<Progress>(this, values)).sendToTarget();
650
}
651
}
652
653
private void finish(Result result) {
654
if (isCancelled()) {
655
onCancelled(result);
656
} else {
657
onPostExecute(result);
658
}
659
mStatus = Status.FINISHED;
660
}
661
662
private static class InternalHandler extends Handler {
663
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
664
@Override
665
public void handleMessage(Message msg) {
666
AsyncTaskResult result = (AsyncTaskResult) msg.obj;
667
switch (msg.what) {
668
case MESSAGE_POST_RESULT:
669
// There is only one result
670
result.mTask.finish(result.mData[0]);
671
break;
672
case MESSAGE_POST_PROGRESS:
673
result.mTask.onProgressUpdate(result.mData);
674
break;
675
}
676
}
677
}
678
679
private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
680
Params[] mParams;
681
}
682
683
@SuppressWarnings({"RawUseOfParameterizedType"})
684
private static class AsyncTaskResult<Data> {
685
final AsyncTask mTask;
686
final Data[] mData;
687
688
AsyncTaskResult(AsyncTask task, Data... data) {
689
mTask = task;
690
mData = data;
691
}
692
}
693
}