AsyncTask兑现原理和内部代码[转]

AsyncTask实现原理和内部代码[转]

AsyncTask实现原理和内部代码??????? }
??? };

??? private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
??????????? MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory); //创建线程池

??? private static final int MESSAGE_POST_RESULT = 0x1;?
??? private static final int MESSAGE_POST_PROGRESS = 0x2;
??? private static final int MESSAGE_POST_CANCEL = 0x3;

??? private static final InternalHandler sHandler = new InternalHandler(); //这个是对Handler的封装，内部处理Thread的状态。

??? private final WorkerRunnable<Params, Result> mWorker;? //该类对Runnable做简单封装
??? private final FutureTask<Result> mFuture; //对于并发库而言FutureTask是最重要的，有兴趣的网友可以看下JDK源码

??? private volatile Status mStatus = Status.PENDING; //保存当前线程状态

??? public enum Status { //枚举类记录当前线程状态
??????? PENDING,
??????? RUNNING,
??????? FINISHED,
??? }

??? public AsyncTask() {
??????? mWorker = new WorkerRunnable<Params, Result>() { //构造Runable对象
??????????? public Result call() throws Exception {
??????????????? Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); //设置线程优先级为后台，这里Android开发网提示大家低于标准线程优先级
??????????????? return doInBackground(mParams);
??????????? }
??????? };

??????? mFuture = new FutureTask<Result>(mWorker) {?
??????????? @Override
??????????? protected void done() {
??????????????? Message message;
??????????????? Result result = null;

??????????????? try {
??????????????????? result = get();
??????????????? } catch (InterruptedException e) { //处理Thread中断异常
??????????????????? android.util.Log.w(LOG_TAG, e);
??????????????? } catch (ExecutionException e) {
??????????????????? throw new RuntimeException("An error occured while executing doInBackground()",
??????????????????????????? e.getCause());
??????????????? } catch (CancellationException e) {
??????????????????? 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);
??????????????? }

??????????????? message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
??????????????????????? new AsyncTaskResult<Result>(AsyncTask.this, result)); //执行完后通过Handler通知结果
??????????????? message.sendToTarget();
??????????? }
??????? };
??? }

??? public final Status getStatus() {
??????? return mStatus;
??? }

??? protected abstract Result doInBackground(Params... params);

??? protected void onPreExecute() {
??? }

??? protected void onPostExecute(Result result) {
??? }

????protected void onProgressUpdate(Progress... values) {
??? }

??? protected void onCancelled() {
??? }

??? public final boolean isCancelled() {
??????? return mFuture.isCancelled();
??? }

??? public final boolean cancel(boolean mayInterruptIfRunning) {
??????? return mFuture.cancel(mayInterruptIfRunning);
??? }

??? public final Result get() throws InterruptedException, ExecutionException {
??????? return mFuture.get();
??? }

??? public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
??????????? ExecutionException, TimeoutException {
??????? return mFuture.get(timeout, unit);
??? }

??? public final AsyncTask<Params, Progress, Result> execute(Params... params) {
??????? 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;

??????? onPreExecute();

??????? mWorker.mParams = params;
??????? sExecutor.execute(mFuture);

??????? return this;
??? }

??? protected final void publishProgress(Progress... values) {?//通过Handler通知UI刷新
??????? sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
??????????????? new AsyncTaskResult<Progress>(this, values)).sendToTarget();
??? }

??? private void finish(Result result) {
??????? if (isCancelled()) result = null;
??????? onPostExecute(result);
??????? mStatus = Status.FINISHED;
??? }

??? private static class InternalHandler extends Handler { //和我们的Handler没有什么不同
??????? @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;
??????????? }
??????? }
??? }

??? private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
??????? Params[] mParams;
??? }

??? @SuppressWarnings({"RawUseOfParameterizedType"})
??? private static class AsyncTaskResult<Data> {
??????? final AsyncTask mTask;
??????? final Data[] mData;

??????? AsyncTaskResult(AsyncTask task, Data... data) {
??????????? mTask = task;
??????????? mData = data;
??????? }
??? }
}

?经过上面的简单分析相信大家对Android AsyncTask会有更加深刻的理解，整个AsyncTask实现基于Thread+Handler，但对于Thread使用的是Java的并发包的FutureTask具体的可以参考JDK5以后的源码。