Android AsyncTask實(shí)現(xiàn)機(jī)制
示例代碼：
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; onPreExecute(); mWorker.mParams = params; exec.execute(mFuture); return this; }execute先調(diào)用onPreExecute()（可見，onPreExecute是自動調(diào)用的）然后調(diào)用exec.execute(mFuture)
public interface Executor { void execute(Runnable command); }這是一個接口，具體實(shí)現(xiàn)在
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); } } }從上面可知，AsyncTask執(zhí)行過程如下：先執(zhí)行onPreExecute，然后交給SerialExecutor執(zhí)行。在SerialExecutor中，先把Runnable添加到mTasks中。
如果沒有Runnable正在執(zhí)行，那么就調(diào)用SerialExecutor的scheduleNext。同時當(dāng)一個Runnable執(zhí)行完以后，繼續(xù)執(zhí)行下一個任務(wù)
AsyncTask中有兩個線程池，THREAD_POOL_EXECUTOR和SERIAL_EXECUTOR，以及一個Handler 主站蜘蛛池模板： 新乐市| 庆城县| 东乡县| 噶尔县| 临澧县| 镇康县| 北流市| 长沙县| 永和县| 尖扎县| 化德县| 长子县| 林州市| 通城县| 九龙县| 平山县| 马公市| 达州市| 甘谷县| 汕头市| 偏关县| 乃东县| 长治市| 进贤县| 昌吉市| 革吉县| 彰化县| 郧西县| 高要市| 荆门市| 蒲江县| 金川县| 尼木县| 高淳县| 宿松县| 辽宁省| 梅州市| 清涧县| 寻甸| 彝良县| 来安县|