闖關(guān)關(guān)卡---第9關(guān)晤柄，闖關(guān)進度20%，繼續(xù)打怪升級
一直以來都沒有使用過AsyncTask矫夷，且因為有Rxjava的存在股冗。雖然說之前有看過AsyncTask知識包括霹陡，但是時間久了也忘記了，今天重新看了一下又有新的認知
1.AsyncTask大致的原理
AsyncTask是使用線程池止状，F(xiàn)utureTask烹棉，CallBack來執(zhí)行任務(wù)，默認的任務(wù)執(zhí)行順序是先進先出(FIFO)
核心線程數(shù)：Math.max(2, Math.min(CPU_COUNT - 1, 4));
最大線程數(shù)：CPU個數(shù)x2+1
存活時間：30s--非核心線程的回收時間怯疤，若allowCoreThreadTimeOut設(shè)置為turn浆洗，也作用在核心線程中
任務(wù)隊列：BlockingQueue<Runnable> sPoolWorkQueue =new LinkedBlockingQueue<Runnable>(128)
2.AsyncTask核心參數(shù)及方法
public abstract class AsyncTask<Params, Progress, Result> {...}
Params：異步任務(wù)參數(shù)
Progress：任務(wù)執(zhí)行進度
Result：任務(wù)執(zhí)行完返回結(jié)果
onPreExecute()：任務(wù)執(zhí)行前的準備工作--主線程
doInBackground(Params... params)：開啟執(zhí)行任務(wù)，返回執(zhí)行的任務(wù)結(jié)果--子線程
onProgressUpdate(Progress... values)：任務(wù)執(zhí)行的進度--主線程
onPostExecute(Result result)：任務(wù)完成的結(jié)果處理集峦，result為doInBackground返回值
3.AsyncTask準備工作--new AsyncTask()
public AsyncTask() {
this((Looper) null);
}
public AsyncTask(@Nullable Handler handler) {
this(handler != null ? handler.getLooper() : null);
}
public AsyncTask(@Nullable Looper callbackLooper) {
mHandler = callbackLooper == null || callbackLooper == Looper.getMainLooper()
? getMainHandler()
: new Handler(callbackLooper);
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
result = doInBackground(mParams);
Binder.flushPendingCommands();
} catch (Throwable tr) {
mCancelled.set(true);
throw tr;
} finally {
postResult(result);
}
return result;
}
};
mFuture = new FutureTask<Result>(mWorker) {
@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);
}
}
};
}
在構(gòu)造函數(shù)中伏社，初始化Handler，實例化WorkerRunnable抽象類---實現(xiàn)CallBack接口塔淤，實例化FutureTask洛口，重寫done()方法，任務(wù)完成時發(fā)送Message凯沪，通過這些操作將任務(wù)裝置在mFuture 中。下面是一個FutureTask簡單例子
public class ThreadMain {
public static void main(String[] args) {
Callable<Integer> callable = new Callable<Integer>() {
@Override
public Integer call() throws Exception {
int i = 0;
try {
for (; i < 2; i++) {
System.out.println(Thread.currentThread().getName() + " " + i);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
System.out.println("任務(wù)完成");
}
return i;
}
};
FutureTask<Integer> task = new FutureTask<Integer>(callable) {
@Override
protected void done() {
System.out.println("任務(wù)完成 done");
super.done();
}
};
task.run();
}
}
4.任務(wù)執(zhí)行
@MainThread
public final AsyncTask<Params, Progress, Result> execute(Params... params) {
return executeOnExecutor(sDefaultExecutor, params);
}
@MainThread
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;
onPreExecute();
mWorker.mParams = params;
exec.execute(mFuture);
return this;
}
在任務(wù)第一次執(zhí)行买优，mStatus 設(shè)置為RUNNING妨马，調(diào)用onPreExecute()在任務(wù)執(zhí)行前的準備工作，exec.execute(mFuture)開啟異步任務(wù)杀赢。接下來看看 sDefaultExecutor 怎么實現(xiàn)的
5.sDefaultExecutor 實現(xiàn)方式
private static class SerialExecutor implements Executor {
final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
Runnable mActive;
public synchronized void execute(final Runnable r) {
mTasks.offer(new Runnable() {
public void run() {
try {
r.run();
} finally {
scheduleNext();
}
}
});
if (mActive == null) {
scheduleNext();
}
}
protected synchronized void scheduleNext() {
if ((mActive = mTasks.poll()) != null) {
THREAD_POOL_EXECUTOR.execute(mActive);
}
}
}
sDefaultExecutor--默認任務(wù)處理器烘跺，ArrayDeque是一個雙向的隊列(FIFO)， mTasks.offer()在最后添加一個任務(wù)元素脂崔，通過mTasks.poll()取得第一個任務(wù)元素使用THREAD_POOL_EXECUTOR線程池來執(zhí)行任務(wù)滤淳。如果要并發(fā)處理調(diào)用executeOnExecutor(Executor exec,Params... params)方法，在參數(shù)1傳入AsyncTask.THREAD_POOL_EXECUTOR
5.handler處理消息
private static class InternalHandler extends Handler {
public InternalHandler(Looper looper) {
super(looper);
}
@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;
}
}
}
handlerMeaage主要任務(wù)處理結(jié)果還有任務(wù)進度砌左，任務(wù)處理結(jié)果已經(jīng)在構(gòu)造函數(shù)實現(xiàn)了脖咐，但是發(fā)送任務(wù)進度消息需要調(diào)用publishProgress(Progress... values)來發(fā)送消息。
protected final void publishProgress(Progress... values) {
if (!isCancelled()) {
getHandler().obtainMessage(MESSAGE_POST_PROGRESS,
new AsyncTaskResult<Progress>(this, values)).sendToTarget();
}
}
