使用
// 定义
private class ExecuteTask extends AsyncTask<String,Integer,Void> {
// 执行线程任务前的操作
@Override
protected void onPreExecute() {
super.onPreExecute();
}
// 后台线程,执行耗时操作。
@Override
protected Void doInBackground(String... strs) {
Log.e(TAG,"线程名称 doInBackground == " + Thread.currentThread().getName());
publishProgress(0);
return null;
}
// 响应 publishProgress 方法。
@Override
protected void onProgressUpdate(Integer... values) {
Log.e(TAG,"线程名称 onProgressUpdate == " + Thread.currentThread().getName());
Log.e(TAG,"onProgressUpdate == " + values);
}
// 后台线程任务执行完成之后,在UI线程的回调方法。
@Override
protected void onPostExecute(Void aVoid) {
Log.e(TAG,"线程名称 onPostExecute == " + Thread.currentThread().getName());
}
// 异步任务取消之后的回调。
@Override
protected void onCancelled() {
super.onCancelled();
}
}
// 开始执行
ExecuteTask executeTask = new ExecuteTask();
executeTask.execute("value1","value2","value3");
源码分析之前你需要知道一些线程的知识点:
带返回值的线程
线程池的一些知识
关于Handler和Looper
关于队列的一些知识
源码分析
①. ExecuteTask executeTask = new ExecuteTask();
// 创建绑定主线程Looper的Handler
mHandler = callbackLooper == null || callbackLooper == Looper.getMainLooper()
? getMainHandler()
: new Handler(callbackLooper);
// WorkerRunnable 实现 Callable,为了创建带返回值的线程
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
mTaskInvoked.set(true);
Result result = null;
try {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
//noinspection unchecked
// 开始执行doInBackground()
result = doInBackground(mParams);
Binder.flushPendingCommands();
} catch (Throwable tr) {
mCancelled.set(true);
throw tr;
} finally {
postResult(result);
}
// 这个值可以在FutureTask.done()方法中通过 get() 方法获取。
return result;
}
};
// 创建带返回值的任务,该任务可提交到线程池。
mFuture = new FutureTask<Result>(mWorker) {
// 异步任务执行完成之后的回调
@Override
protected void done() {
try {
postResultIfNotInvoked(get());
} catch (InterruptedException e) {
android.util.Log.w(LOG_TAG, e);
} catch (ExecutionException e) {
throw new RuntimeException("An error occurred while executing doInBackground()",
e.getCause());
} catch (CancellationException e) {
postResultIfNotInvoked(null);
}
}
};
}
②. executeTask.execute(“value1”,“value2”,“value3”);
public final AsyncTask<Params, Progress, Result> execute(Params... params) {
return executeOnExecutor(sDefaultExecutor, params);
}
public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
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;
// 异步任务开始之前的调用
onPreExecute();
mWorker.mParams = params;
// exec == sDefaultExecutor == SerialExecutor
// mFuture == FutureTask
exec.execute(mFuture);
return this;
}
public static final Executor SERIAL_EXECUTOR = new SerialExecutor();
private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
private static class SerialExecutor implements Executor {
final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
Runnable mActive;
public synchronized void execute(final Runnable r) {
// 将任务加入到队列中
mTasks.offer(new Runnable() {
public void run() {
try {
// 执行mFuture (FutureTask)
r.run();
} finally {
scheduleNext();
}
}
});
if (mActive == null) {
// 没有可执行任务时,调用。
scheduleNext();
}
}
protected synchronized void scheduleNext() {
// 将队列中的任务取出。
if ((mActive = mTasks.poll()) != null) {
// 执行任务 THREAD_POOL_EXECUTOR == ThreadPoolExecutor
THREAD_POOL_EXECUTOR.execute(mActive);
}
}
}
// 创建线程池。
private static final BlockingQueue<Runnable> sPoolWorkQueue =
new LinkedBlockingQueue<Runnable>(128);
public static final Executor THREAD_POOL_EXECUTOR;
static {
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,
sPoolWorkQueue, sThreadFactory);
threadPoolExecutor.allowCoreThreadTimeOut(true);
THREAD_POOL_EXECUTOR = threadPoolExecutor;
}
// THREAD_POOL_EXECUTOR.execute(mActive); 执行之后 FutureTask.do() 方法被执行。
// postResultIfNotInvoked(get())
private void postResultIfNotInvoked(Result result) {
final boolean wasTaskInvoked = mTaskInvoked.get();
if (!wasTaskInvoked) {
postResult(result);
}
}
private Result postResult(Result result) {
@SuppressWarnings("unchecked")
Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(this, result));
message.sendToTarget();
return result;
}
private static class AsyncTaskResult<Data> {
final AsyncTask mTask;
final Data[] mData;
AsyncTaskResult(AsyncTask task, Data... data) {
mTask = task;
mData = data;
}
}
private static class InternalHandler extends Handler {
public InternalHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
AsyncTaskResult<?> result = (AsyncTaskResult<?>) msg.obj;
switch (msg.what) {
// 执行完成之后的消息
case MESSAGE_POST_RESULT:
// There is only one result
result.mTask.finish(result.mData[0]);
break;
// publishProgress 执行
case MESSAGE_POST_PROGRESS:
result.mTask.onProgressUpdate(result.mData);
break;
}
}
}
private void finish(Result result) {
if (isCancelled()) {
onCancelled(result);
} else {
onPostExecute(result);
}
mStatus = Status.FINISHED;
}