- /*
- *
- */
- public abstract class AsyncTask < Params,
- Progress,
- Result > {
- //Params是传入的参数,Progress用于显示进度 ,Result则为doinBackground传递给Post的参数
- private static final String LOG_TAG = "AsyncTask";
- //线程池维护线程的最少数量
- private static final int CORE_POOL_SIZE = 5;
- //线程池维护线程的最大数量
- private static final int MAXIMUM_POOL_SIZE = 128;
- //线程池维护线程所允许的空闲时间
- private static final int KEEP_ALIVE = 10;
- //线程池所使用的缓冲队列
- private static final BlockingQueue < Runnable > sWorkQueue = new LinkedBlockingQueue < Runnable > (10);
- private static final ThreadFactory sThreadFactory = new ThreadFactory() {
- private final AtomicInteger mCount = new AtomicInteger(1);
- public Thread newThread(Runnable r) {
- return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
- }
- };
- //TimeUnit.SECONDS线程池维护线程所允许的空闲时间的单位
- private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);
- private static final int MESSAGE_POST_RESULT = 0x1;
- private static final int MESSAGE_POST_PROGRESS = 0x2;
- private static final int MESSAGE_POST_CANCEL = 0x3;
- //因为整个AsyncTask是在UI线程创建的,所以sHandler对应到UI线程Message Queue,所以可以更新UI
- private static final InternalHandler sHandler = new InternalHandler();
- private final WorkerRunnable < Params,
- Result > mWorker;
- private final FutureTask < Result > mFuture;
- private volatile Status mStatus = Status.PENDING;
- /**
- * Indicates the current status of the task. Each status will be set only once
- * during the lifetime of a task.
- */
- public enum Status {
- /**
- * Indicates that the task has not been executed yet.
- * 还没有被execute
- */
- PENDING,
- /**
- * 运行中
- * Indicates that the task is running.
- */
- RUNNING,
- /**
- * onPostExecute 执行完毕,这些线程其实是没法终止的
- * Indicates that {@link AsyncTask#onPostExecute} has finished.
- */
- FINISHED,
- }
- /**
- * 异步的任务,必须是在UI线程创建
- * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
- */
- public AsyncTask() {
- //参数和结果队,是一个runnable用来执行后台任务,调用doInBackground
- //WorkerRunnable是一个继承自Callable<Result>带有回调功能的类
- mWorker = new WorkerRunnable < Params,
- Result > () {
- public Result call() throws Exception {
- Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
- return doInBackground(mParams);
- }
- };
- //sExecutor.execute(mFuture)会先执行带有回调的mWorker,执行完毕之后会执行done()方法
- mFuture = new FutureTask < Result > (mWorker) {@Override protected void done() {
- Message message;
- Result result = null;
- try {
- result = get();
- } catch(InterruptedException e) {
- //线程被Interrupt了
- android.util.Log.w(LOG_TAG, e);
- } catch(ExecutionException e) {
- //执行异常
- throw new RuntimeException("An error occured while executing doInBackground()", e.getCause());
- } catch(CancellationException e) {
- //执行cancel?通过sendToTarget
- message = sHandler.obtainMessage(MESSAGE_POST_CANCEL, new AsyncTaskResult < Result > (AsyncTask.this, (Result[]) null));
- message.sendToTarget();
- return;
- } catch(Throwable t) {
- throw new RuntimeException("An error occured while executing " + "doInBackground()", t);
- }
- //通过sendMessage和Handler配合完成doInBackground和onPostExecute的关联
- message = sHandler.obtainMessage(MESSAGE_POST_RESULT, new AsyncTaskResult < Result > (AsyncTask.this, result));
- message.sendToTarget();
- }
- };
- }
- /**
- * Returns the current status of this task.
- *
- * @return The current status.
- */
- public final Status getStatus() {
- return mStatus;
- }
- /**
- * Override this method to perform a computation on a background thread. The
- * specified parameters are the parameters passed to {@link #execute}
- * by the caller of this task.
- *
- * This method can call {@link #publishProgress} to publish updates
- * on the UI thread.
- *
- * @param params The parameters of the task.
- *
- * @return A result, defined by the subclass of this task.
- *
- * @see #onPreExecute()
- * @see #onPostExecute
- * @see #publishProgress
- */
- protected abstract Result doInBackground(Params...params);
- /**
- * Runs on the UI thread before {@link #doInBackground}.
- *
- * @see #onPostExecute
- * @see #doInBackground
- */
- protected void onPreExecute() {}
- /**
- * Runs on the UI thread after {@link #doInBackground}. The
- * specified result is the value returned by {@link #doInBackground}
- * or null if the task was cancelled or an exception occured.
- *
- * @param result The result of the operation computed by {@link #doInBackground}.
- *
- * @see #onPreExecute
- * @see #doInBackground
- */
- @SuppressWarnings({
- "UnusedDeclaration"
- }) protected void onPostExecute(Result result) {}
- /**
- * Runs on the UI thread after {@link #publishProgress} is invoked.
- * The specified values are the values passed to {@link #publishProgress}.
- *
- * @param values The values indicating progress.
- *
- * @see #publishProgress
- * @see #doInBackground
- */
- @SuppressWarnings({
- "UnusedDeclaration"
- }) protected void onProgressUpdate(Progress...values) {}
- /**
- * Runs on the UI thread after {@link #cancel(boolean)} is invoked.
- *
- * @see #cancel(boolean)
- * @see #isCancelled()
- */
- protected void onCancelled() {}
- /**
- * Returns <tt>true</tt> if this task was cancelled before it completed
- * normally.
- * 判断是否被cancel了
- *
- * @return <tt>true</tt> if task was cancelled before it completed
- *
- * @see #cancel(boolean)
- */
- public final boolean isCancelled() {
- return mFuture.isCancelled();
- }
- /**
- * Attempts to cancel execution of this task. This attempt will
- * fail if the task has already completed, already been cancelled,
- * or could not be cancelled for some other reason. If successful,
- * and this task has not started when <tt>cancel</tt> is called,
- * this task should never run. If the task has already started,
- * then the <tt>mayInterruptIfRunning</tt> parameter determines
- * whether the thread executing this task should be interrupted in
- * an attempt to stop the task.
- *
- * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
- * task should be interrupted; otherwise, in-progress tasks are allowed
- * to complete.
- *
- * @return <tt>false</tt> if the task could not be cancelled,
- * typically because it has already completed normally;
- * <tt>true</tt> otherwise
- *
- * @see #isCancelled()
- * @see #onCancelled()
- */
- public final boolean cancel(boolean mayInterruptIfRunning) {
- return mFuture.cancel(mayInterruptIfRunning);
- }
- /**
- * Waits if necessary for the computation to complete, and then
- * retrieves its result.
- *
- * @return The computed result.
- *
- * @throws CancellationException If the computation was cancelled.
- * @throws ExecutionException If the computation threw an exception.
- * @throws InterruptedException If the current thread was interrupted
- * while waiting.
- */
- public final Result get() throws InterruptedException,
- ExecutionException {
- return mFuture.get();
- }
- /**
- * Waits if necessary for at most the given time for the computation
- * to complete, and then retrieves its result.
- *
- * @param timeout Time to wait before cancelling the operation.
- * @param unit The time unit for the timeout.
- *
- * @return The computed result.
- *
- * @throws CancellationException If the computation was cancelled.
- * @throws ExecutionException If the computation threw an exception.
- * @throws InterruptedException If the current thread was interrupted
- * while waiting.
- * @throws TimeoutException If the wait timed out.
- */
- public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
- ExecutionException,
- TimeoutException {
- return mFuture.get(timeout, unit);
- }
- /**
- * Executes the task with the specified parameters. The task returns
- * itself (this) so that the caller can keep a reference to it.
- *
- * This method must be invoked on the UI thread.
- *
- * @param params The parameters of the task.
- *
- * @return This instance of AsyncTask.
- *
- * @throws IllegalStateException If {@link #getStatus()} returns either
- * {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
- */
- public final AsyncTask < Params,
- Progress,
- Result > execute(Params...params) {
- //只能执行一次,重复执行会抛出异常
- if (mStatus != Status.PENDING) {
- switch (mStatus) {
- case RUNNING:
- throw new IllegalStateException("Cannot execute task:" + " the task is already running.");
- case FINISHED:
- throw new IllegalStateException("Cannot execute task:" + " the task has already been executed " + "(a task can be executed only once)");
- }
- }
- mStatus = Status.RUNNING;
- //这是决定AsyncTask执行顺序逻辑的关键类,先pre,后doInBack,由back调用post
- onPreExecute();
- mWorker.mParams = params;
- sExecutor.execute(mFuture);
- return this;
- }
- /**
- * This method can be invoked from {@link #doInBackground} to
- * publish updates on the UI thread while the background computation is
- * still running. Each call to this method will trigger the execution of
- * {@link #onProgressUpdate} on the UI thread.
- *
- * @param values The progress values to update the UI with.
- *
- * @see #onProgressUpdate
- * @see #doInBackground
- */
- protected final void publishProgress(Progress...values) {
- sHandler.obtainMessage(MESSAGE_POST_PROGRESS, new AsyncTaskResult < Progress > (this, values)).sendToTarget();
- }
- //这是一个私有方法,不由外部调用
- private void finish(Result result) {
- if (isCancelled()) result = null;
- onPostExecute(result);
- //表示post方法已经执行完毕
- mStatus = Status.FINISHED;
- }
- //由这个handler来处理后台runnable发送的msg
- private static class InternalHandler extends Handler {@SuppressWarnings({
- "unchecked",
- "RawUseOfParameterizedType"
- })@Override public void handleMessage(Message msg) {
- AsyncTaskResult result = (AsyncTaskResult) msg.obj;
- switch (msg.what) {
- case MESSAGE_POST_RESULT:
- // There is only one result
- result.mTask.finish(result.mData[0]);
- break;
- case MESSAGE_POST_PROGRESS:
- result.mTask.onProgressUpdate(result.mData);
- break;
- case MESSAGE_POST_CANCEL:
- result.mTask.onCancelled();
- break;
- }
- }
- }
- //使用的了回调,这个值得学习
- private static abstract class WorkerRunnable < Params,
- Result > implements Callable < Result > {
- Params[] mParams;
- }
- //异步任务结果类
- @SuppressWarnings({
- "RawUseOfParameterizedType"
- }) private static class AsyncTaskResult < Data > {
- final AsyncTask mTask;
- final Data[] mData;
- AsyncTaskResult(AsyncTask task, Data...data) {
- mTask = task;
- mData = data;
- }
- }
- }
来源: http://lib.csdn.net/snippet/android/49945