AsyncTask实现代码原理

本文主要是介绍AsyncTask实现代码原理，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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 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(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(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(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;

}

prot
ected final void publishProgress(Progress… values) { //通过Handler通知UI刷新

sHandler.obtainMessage(MESSAGE_POST_PROGRESS,

new AsyncTaskResult(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

最后

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一个人可以走的很快，但一群人才能走的更远！不论你是正从事IT行业的老鸟或是对IT行业感兴趣的新人

都欢迎加入我们的的圈子（技术交流、学习资源、职场吐槽、大厂内推、面试辅导），让我们一起学习成长！

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