邯郸钢铁招聘,9c8822,鞋垫花
android asynctask实现机制
示例代码：
我要评论
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先调用onpreexecute()（可见，onpreexecute是自动调用的）然后调用exec.execute(mfuture)
public interface executor {
void execute(runnable command);
}
这是一个接口，具体实现在
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);
}
}
}
从上面可知，asynctask执行过程如下：先执行onpreexecute，然后交给serialexecutor执行。在serialexecutor中，先把runnable添加到mtasks中。
如果没有runnable正在执行，那么就调用serialexecutor的schedulenext。同时当一个runnable执行完以后，继续执行下一个任务
asynctask中有两个线程池，thread_pool_executor和serial_executor，以及一个handler–internalhandler
/**
* an {@link executor} that can be used to execute tasks in parallel.
*/
public static final executor thread_pool_executor
= new threadpoolexecutor(core_pool_size, maximum_pool_size, keep_alive,
timeunit.seconds, spoolworkqueue, sthreadfactory);
/**
* an {@link executor} that executes tasks one at a time in serial
* order. this serialization is global to a particular process.
*/
public static final executor serial_executor = new serialexecutor();
private static internalhandler shandler;
serial_executor用于任务的排列，thread_pool_executor真正执行线程，internalhandler用于线程切换
先看构造函数
public asynctask() {
mworker = new workerrunnable<params, result>() {
public result call() throws exception {
mtaskinvoked.set(true);
process.setthreadpriority(process.thread_priority_background);
//noinspection unchecked
return postresult(doinbackground(mparams));
}
};
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 occured while executing doinbackground()",
e.getcause());
} catch (cancellationexception e) {
postresultifnotinvoked(null);
}
}
};
}
看到了熟悉的doinbackground了吧，然后调用postresult
private result postresult(result result) {
@suppresswarnings("unchecked")
message message = gethandler().obtainmessage(message_post_result,
new asynctaskresult<result>(this, result));
message.sendtotarget();
return result;
}
主线程中创建internalhandler并发送message_post_result消息，然后调用finish函数
private static class internalhandler extends handler {
public internalhandler() {
super(looper.getmainlooper());
}
@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;
}
}
}
private void finish(result result) {
if (iscancelled()) {
oncancelled(result);
} else {
onpostexecute(result);
}
mstatus = status.finished;
}
finish中调用onpostexecute。
asynctask工作流程：new mythread().execute(1);
先构造函数，然后execute
构造函数只是准备了mworker和mfuture这两个变量
execute中调用onpreexecute，然后exec.execute(mfuture)，其中响应了call函数，call中调用doinbackground，然后将结果传给handler然后finish掉，finish函数调用onpostexecute
你可能会奇怪，为什么没有onprogressupdate，有注解可以解释
/**
* runs on the ui thread after {@link #publishprogress} is invoked.
* the specified values are the values passed to {@link #publishprogress}.
*
* @param values the values indicating progress.
*
* @see #publishprogress
* @see #doinbackground
*/
@suppresswarnings({"unuseddeclaration"})
protected void onprogressupdate(progress... values) {
}
也就是说必须调用publishprogress才会自动调用onprogressupdate。
那如何调用publishprogress呢？
/**
* override this method to perform a computation on a background thread. the
* specified parameters are the parameters passed to {@link #execute}
* by the caller of this task.
*
* this method can call {@link #publishprogress} to publish updates
* on the ui thread.
*
* @param params the parameters of the task.
*
* @return a result, defined by the subclass of this task.
*
* @see #onpreexecute()
* @see #onpostexecute
* @see #publishprogress
*/
protected abstract result doinbackground(params... params);
doinbackground说的很明确，在doinbackground函数里面显示调用publishprogress即可。
publishprogress源码：
protected final void publishprogress(progress... values) {
if (!iscancelled()) {
gethandler().obtainmessage(message_post_progress,
new asynctaskresult<progress>(this, values)).sendtotarget();
}
}
private static class internalhandler extends handler {
public internalhandler() {
super(looper.getmainlooper());
}
@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:
//****************************************在这里调用
result.mtask.onprogressupdate(result.mdata);
break;
}
}
}
感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！
如对本文有疑问，请在下面进行留言讨论，广大热心网友会与你互动！！ 点击进行留言回复
Android studio开发小型对话机器人app(实例代码)
Android通过Java sdk的方式接入OpenCv的方法
Android 通过cmake的方式接入opencv的方法步骤
Android Studio finish()方法的使用与解决app点击“返回”(直接退出)
Android 进度条 ProgressBar的实现代码(隐藏、出现、加载进度)
网友评论