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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