关于线程的问题在Android中使用AsyncTask停止或不在progressDialog中

Question

I have a code as following, and the thing is every time I cancel the dialog, InterruptException occurs and the cancel method doesn't really work. As I shows below, I print the state of cancel in the onPostExecute method, it is a false instead of true. Before adding isRunning parameter, obviously the thread was still running in the background. Although isRunning does stop the thread( the onPostExecute method was executed), I want to know why the exception happened and why I still got a false in the isCanceled method. Thanks!

public void startDownload(View view){
    dialog = new ProgressDialog(this);
    final Downloader downloader = new Downloader(this, dialog);
    downloader.execute(0);
    dialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
        @Override
        public void onCancel(DialogInterface dialog) {
            downloader.cancel(true);
        }
    });
}

public class Downloader extends AsyncTask<Integer, Integer, String> {
private Context context;
private PowerManager.WakeLock wakeLock;
private ProgressDialog dialog;
public boolean isRunning = true;

public Downloader(Context context, ProgressDialog dialog) {
    this.context = context;
    this.dialog = dialog;
}

@Override
protected void onPreExecute() {
    super.onPreExecute();
    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    wakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
            getClass().getName());
    wakeLock.acquire();

    dialog.setMessage("Downloading...");
    dialog.setIndeterminate(true);
    dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    dialog.setCancelable(false);
    dialog.setButton(ProgressDialog.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            isRunning = false;
        }
    });
    dialog.show();
}

@Override
protected String doInBackground(Integer[] params) {
    int count = params[0];
    while(count<100 && isRunning){
        publishProgress(count);
        try{
            count++;
            System.out.println(count);
            Thread.sleep(200);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    return null;
}

@Override
protected void onProgressUpdate(Integer... values) {
    super.onProgressUpdate(values);
    dialog.setIndeterminate(false);
    dialog.setMax(100);
    dialog.setProgress(values[0]);
}

@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    wakeLock.release();
    dialog.dismiss();
    if (s != null)
        Toast.makeText(context,"Download error: "+ s, Toast.LENGTH_LONG).show();
    else
        Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
    System.out.println(isCancelled());
}

}

Answer 1

Make sure you're not executing another AsyncTask, or start this one in parallel, using .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR) instead of .execute() . Otherwise, if you're already running another AsyncTask in background this other one will not run until that last one finishes.

On the other hand, try not to track AsyncTask lifecycle status with a custom boolean, to do so, use isCancelled() to check stuff at runtime or break any loop and if required, override the AsyncTask's onCancelled() method to implement any functionality you may need at that point.

Don't forget to check the reference: AsyncTask - Android Developers .