Question

I get a crash “Can’t create handler inside thread that has not called Looper.prepare()” in a onPreExecute in a thread. It was my understanding that onPreExecute runs on the UI Thread, so how can it crash?

public void onPreExecute() {
        if (loading == null || !loading.isShowing())
            loading = ProgressDialog.show(co, "",
                    "Retrieving Geolocation...", true);
    }

Quite strangely, it works sometimes, and sometimes not

Answer 1

AsyncTask Threading rules (few paragraphs down) state:

• 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.)

My guess is that you called execute() on background thread.