当活动处于 onPause 生命周期时尝试运行 aynktask

Question

I need to make a notification when my DB gets change and I cant use firebase in this project so I try to make a solution here : (if I make asynktask for check DB and it repeats periodically then the problem is solved) but I have crush when I try to run asynktask when activity is in onPause() situation, it doesn't work!!!

@Override
public void onPause() {
    super.onPause();
    Handler handler = new Handler();
    handler.postDelayed(new Runnable() {
        @Override
        public void run() {
            new push_notification().execute();
        }
    }, 5000);
}

.................................

private class push_notification extends AsyncTask < Void, Void, Void > {
    HashMap < String,
    String > contact;

    ContactsContract.Contacts contacts;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("please wait ...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

    @Override
    protected Void doInBackground(Void...arg0) {
        ///////////////////////////////
        contactList = new ArrayList < > ();

        HttpHandler sh = new HttpHandler();

        String link;
        String data = "";
        BufferedReader bufferedReader;
        String result;

        try {
            data = "?id=" + URLEncoder.encode("199", "UTF-8");
        } catch (Exception e) {}
        url4 = "http://www.xxxxxxxxxxxxxxxxx.php" + data;
        jsonStr = sh.makeServiceCall(url4);

        if (jsonStr != null) {

            try {
                JSONArray contacts = new JSONArray(jsonStr);
                // looping through All Contacts
                for (int i = 0; i < contacts.length(); i++) {
                    JSONObject c = contacts.getJSONObject(i);
                    pre_post_id = c.getString("id");
                    pre_phone = c.getString("phone");
                    pre_username = c.getString("username");
                    pre_pic = c.getString("pic");
                    pre_date = c.getString("date");
                    pre_follow_askers = c.getString("follow_askers");

                    contact = new HashMap < > ();
                    // adding each child node to HashMap key => value
                    contact.put("id", pre_post_id);
                    contact.put("phone", pre_phone);
                    contact.put("username", pre_username);
                    contact.put("pic", pre_pic);
                    contact.put("date", pre_date);
                    contact.put("follow_askers", pre_follow_askers);

                    // adding contact to contact list
                    contactList.add(contact);
                }
            } catch (final JSONException e) {
                //Log.e(TAG, "Json parsing error: " + e.getMessage());                    
            }
        } else {}
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        toast(pre_phone);
    }
}

Does anyone have an idea how can I do this?

Answer 1

You'll need to rethink your design a bit to respect the Activity Lifecycle. By definition, you shouldn't be doing anything in the UI from a paused activity.

Also, AsyncTask is going to give you a lot of trouble - I suggest that you stay away from it completely and find a better way to do background processing. I suggest a background service.

You should also seriously consider getting rid of the progress dialog and the toast. What you have here is a background task that's really not connected to any piece of the UI, and trying to keep it connected to the UI is probably going to cause you endless problems.