AsyncTask源码阅读

来源：互联网发布：linux五笔输入法安装编辑：程序博客网时间：2024/05/21 09:58

execute 方法
最终调用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;    }

开始会调用我们自己实现的 onPreExecute() 然后通过exec.execute(mFuture) 的方式执行线程

构造过程

public AsyncTask() {        mWorker = new WorkerRunnable<Params, Result>() {            public Result call() throws Exception {                mTaskInvoked.set(true);                Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);                //noinspection unchecked                Result result = doInBackground(mParams);                Binder.flushPendingCommands();                return postResult(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);                }            }        };    }

mWorker 其实是callable类型（与线程相关的一个类）在该对象构造中调用了我们自己实现的doInBackground(mParams); 然后调用了Binder.flushPendingCommands(); 将线程发送到内核，最后 postResult（）发送消息给handler.

然后创建FutureTask 对象（与线程相关的类）调用了postResultIfNotInvoked(get()); 作用与上面一样都调用了postResult（）只是需要在 !wasTaskInvoked 的情况下调用

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