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我使用AsyncTask来执行耗时的操作,操作扫描SD卡并将所有有效的照片绝对路径添加到ArrayList容器。我把操作放到AsyncTask中执行。耗时的操作Utils.getPhotoList();
被置于doInbackgroud
方法下。返回值按照onPostExecute
方法分配给全局变量list
。从日志中,我知道该方法已执行,并为list
分配了一个值。但为什么onStartCommand
方法下的全局变量list
始终是null
,这使我困惑不已。请参阅下面的代码。android asynctask does not work
ConcurrentAsyncTask.execute(new PhotoTask());
和完整的代码是
public int onStartCommand(Intent intent, int flags, int startId) {
if (isCameraUpload) {
// execute time-consuming operation
ConcurrentAsyncTask.execute(new PhotoTask());
}
// list is always null
if (list != null) {
notifyUser(photosCount, repoName);
}
return START_STICKY;
}
和定制类ConcurrentAsyncTask是。
public class ConcurrentAsyncTask {
public static <T> void execute(AsyncTask<T, ?, ?> task, T...args) {
if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.HONEYCOMB_MR1) {
task.execute(args);
} else {
task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, args);
}
}
public static void execute(Runnable runnable) {
execute(new SimpleAsyncTask(runnable));
}
private static class SimpleAsyncTask extends AsyncTask<Void, Void, Void> {
Runnable runnable;
public SimpleAsyncTask(Runnable runnable) {
this.runnable = runnable;
}
public Void doInBackground(Void... args) {
try {
runnable.run();
} catch(Exception e) {
// ignore
}
return null;
}
}
和PhotoTask
类是
private class PhotoTask extends AsyncTask<Void, Void, List<SelectableFile>> {
@Override
protected List<SelectableFile> doInBackground(Void... params) {
Log.d(DEBUG_TAG, "doInBackgroud");
Log.d(DEBUG_TAG, "doInBackgroud:pathList.size: " + Utils.getPhotoList().size());
return Utils.getPhotoList();
}
@Override
protected void onPostExecute(List<SelectableFile> result) {
Log.d(DEBUG_TAG, "onPostExecute");
list = result;
Log.d(DEBUG_TAG, "onPostExecute: list.size: " + list.size());
}
}
任何反馈将不胜感激。谢谢!
这是因为您在启动AsyncTask后立即检查列表变量,该变量在那里将为空或空。您需要将此检查放在AsyncTask的onPostExecute方法中,然后从那里启动任何其他进程。如果你的AsyncTask在另一个类然后你的活动,那么你可以使用接口来通知呼叫类 – 2014-09-02 10:48:44
@RajenRaiyarela这节省了我,谢谢! – 2014-09-02 10:55:24