Stopping AsyncTask in Android

Issue

I am trying to stop an AsyncTask in Android. In doInBackground it runs through an IP - Address list and tries to ping all of them.

Furthermore, when executing the AsyncTask a ProgressDialog opens which you can cancel. Calling this cancel - text calls the onCancelled method in AsyncTask. So, this method is being called, but it seems as if it is never stopped because when I hit the button Find again, I always get the following error message:

java.lang.IllegalStateException: Cannot execute task: the task has already been executed (a task can be executed only once)

Here is my code:

private Settings.HostWorker hostWorker;

private void initComponents() {
    hostWorker = new Settings.HostWorker();
    progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        dialog.dismiss();
        if(!hostWorker.isCancelled()) {
            hostWorker.cancel(true);
        }
    }
});
}

findServerButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v)
    {
        if(findServerButton.isClickable()) {
            progressDialog.show();
            hostWorker.execute();
            findServerButton.setClickable(false);
        }
    }
});

private class HostWorker extends AsyncTask<Integer, String, Void> {
    @Override
    protected Void doInBackground(Integer... params) {
        try {
            for (int i = 0; i <= 255; i++) {
                String ip = createHostsList(i);
                if (ip != null) {
                    publishProgress(ip);
                }
                if(isCancelled())
                {
                    break;
                }
            }
        } catch (Exception e) {
    MyAlertDialog myAlertDialog = new MyAlertDialog(getBaseContext(),     "Error in Settings - doInBackground: " + e.getMessage());
    myAlertDialog.showAlertDialog();
    }
    return null;
}
protected void onProgressUpdate(String... values) {
    hostsOnline.add(values[0]);
    settingsCustomArrayAdapter.notifyDataSetChanged();
}

protected void onCancelled(){
    findServerButton.setClickable(true);
}

@Override
protected void onPostExecute(Void aVoid)
{
    super.onPostExecute(aVoid);
}
}

Solution

The error

Cannot execute task: the task has already been executed (a task can be executed only once)

suggests that you need to create a new HostWorker instance each time you want to run the task. You could achieve this by removing the line

hostWorker = new Settings.HostWorker();

from initComponents and instead adding it into your findServerButton OnClickListener like so:

findServerButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v)
    {
        if(findServerButton.isClickable()) {
            progressDialog.show();
            hostworker = new Settings.HostWorker(); // Line added here.
            hostWorker.execute();
            findServerButton.setClickable(false);
        }
    }
});

Answered By - stkent