我已经通过以下代码安排了AsyncTask使用Timer
public void toCallAsynchronous() {
TimerTask doAsynchronousTask;
final Handler handler = new Handler();
Timer timer = new Timer();
doAsynchronousTask = new TimerTask() {
@Override
public void run() {
// TODO Auto-generated method stub
handler.post(new Runnable() {
public void run() {
try {
if(mLoggedIn)
{
DownloadRandomPicture download = new DownloadRandomPicture(this, mApi, CLIENT_ID, mImage);
download.execute();
}
} catch (Exception e) {
// TODO Auto-generated catch block
}
}
});
}
};
timer.schedule(doAsynchronousTask, 0,50000);//execute in every 50000 ms
}
@Override
protected Boolean doInBackground(Void... params) {
try {
if (mCanceled) {
return false;
}
// Get the metadata for a directory
Entry dirent = mApi.metadata(mPath, 1000, null, true, null);
if (!dirent.isDir || dirent.contents == null) {
// It's not a directory, or there's nothing in it
mErrorMsg = "File or empty directory";
return false;
}
// Make a list of everything in it that we can get a thumbnail for
ArrayList<Entry> thumbs = new ArrayList<Entry>();
for (Entry ent: dirent.contents) {
if (ent.thumbExists) {
// Add it to the list of thumbs we can choose from
thumbs.add(ent);
}
}
if (mCanceled) {
return false;
}
if (thumbs.size() == 0) {
// No thumbs in that directory
mErrorMsg = "No pictures in that directory";
return false;
}
// Now pick a random one
int index = (int)(Math.random() * thumbs.size());
Entry ent = thumbs.get(index);
String path = ent.path;
mFileLen = ent.bytes;
String cachePath = mContext.getCacheDir().getAbsolutePath() + "/" + IMAGE_FILE_NAME;
try {
mFos = new FileOutputStream(cachePath);
} catch (FileNotFoundException e) {
mErrorMsg = "Couldn't create a local file to store the image";
return false;
}
// This downloads a smaller, thumbnail version of the file. The
// API to download the actual file is roughly the same.
mApi.getThumbnail(path, mFos, ThumbSize.BESTFIT_960x640,
ThumbFormat.JPEG, null);
if (mCanceled) {
return false;
}
mDrawable = Drawable.createFromPath(cachePath);
// We must have a legitimate picture
return true;
} catch (DropboxUnlinkedException e) {
// The AuthSession wasn't properly authenticated or user unlinked.
} catch (DropboxPartialFileException e) {
// We canceled the operation
mErrorMsg = "Download canceled";
} catch (DropboxServerException e) {
// Server-side exception. These are examples of what could happen,
// but we don't do anything special with them here.
if (e.error == DropboxServerException._304_NOT_MODIFIED) {
// won't happen since we don't pass in revision with metadata
} else if (e.error == DropboxServerException._401_UNAUTHORIZED) {
// Unauthorized, so we should unlink them. You may want to
// automatically log the user out in this case.
} else if (e.error == DropboxServerException._403_FORBIDDEN) {
// Not allowed to access this
} else if (e.error == DropboxServerException._404_NOT_FOUND) {
// path not found (or if it was the thumbnail, can't be
// thumbnailed)
} else if (e.error == DropboxServerException._406_NOT_ACCEPTABLE) {
// too many entries to return
} else if (e.error == DropboxServerException._415_UNSUPPORTED_MEDIA) {
// can't be thumbnailed
} else if (e.error == DropboxServerException._507_INSUFFICIENT_STORAGE) {
// user is over quota
} else {
// Something else
}
// This gets the Dropbox error, translated into the user's language
mErrorMsg = e.body.userError;
if (mErrorMsg == null) {
mErrorMsg = e.body.error;
}
} catch (DropboxIOException e) {
// Happens all the time, probably want to retry automatically.
mErrorMsg = "Network error. Try again.";
} catch (DropboxParseException e) {
// Probably due to Dropbox server restarting, should retry
mErrorMsg = "Dropbox error. Try again.";
} catch (DropboxException e) {
// Unknown error
mErrorMsg = "Unknown error. Try again.";
}
return false;
}
protected void onProgressUpdate(Long... progress) {
int percent = (int)(100.0*(double)progress[0]/mFileLen + 0.5);
//mDialog.setProgress(percent);
}
@Override
protected void onPostExecute(Boolean result) {
//mDialog.dismiss();
if (result) {
// Set the image now that we have it
mView.setImageDrawable(mDrawable);
} else {
// Couldn't download it, so show an error
showToast(mErrorMsg);
}
}
我从onCreate我的活动中调用这个。我的异步任务基本上是从服务器下载一些数据。主要活动允许用户登录到服务器，然后我去获取数据。我面临的问题是每个 AsyncTask 创建自己的线程。此外，这些都没有完成。线程状态始终在运行。有没有办法检查新的 AsyncTask 仅在较早完成时才启动。