Question

Say I am running

new CommentList().execute(url);

If I am in the doInBackground method and I catch a Null value and inside that null value exception I try running the same one again:

new CommentList().execute(url);

Will it stop running the first one?

Can I do this:

if (result == null) {
    cancel(true);                           
    }

@Override
    protected void onCancelled() {
        new CommentList().execute(commentlinkurl);
    }

Basically I don’t want the onPostExecute to run if it gets cancelled.

Answer 1

This is not a good idea. You should not be creating new task on a non-UI thread (from within doInBackground method).

From docs:

There are a few threading rules that must be
followed for this class to work properly:

• The task instance must be created on the UI thread.
• execute(Params…) must be invoked on the UI thread.
• Do not call onPreExecute(), onPostExecute(Result), doInBackground(Params…), onProgressUpdate(Progress…) manually.
• The task can be executed only once (an exception will be thrown if a second execution is attempted.)

Edit based on comments:
You can however start the task again inside onPostExecute or onCancelled method. You can simply return some specific result to it from doInBackground or save your Throwable in the AsyncTask member variable to analyze it further:

protected void onPostExecute(Something something) {
    if(something == null){
        // safe to start new execute task here
    }
    // or
    if(mException instanceof TemporaryIssueException){
        // safe to start new execute task here
    }
}