How can i call Toast.makeText() according to result of AsyncTask in protected String doInBackground method?

Question

I fetched data from the database in AsyncTask and if it is null, I want to Toast a warning text. I tried in AsyncTask but i learned that it isn't called in a worker thread. Here is my doInBackground method:

protected String doInBackground(Boolean... params) {
        String result = null;
        StringBuilder sb = new StringBuilder();
        try {   
            HttpClient httpclient = new DefaultHttpClient();
            HttpGet httppost = new HttpGet( "http://191.162.2.235/getProducts.php?login=1&user_name="+UserName+"&user_pass="+Password);
            HttpResponse response = httpclient.execute(httppost);
            if (response.getStatusLine().getStatusCode() != 200) {
                Log.d("MyApp", "Server encountered an error");
            }
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(
                            response.getEntity().getContent(), "UTF8"));  
            sb = new StringBuilder();
            sb.append(reader.readLine() + "\n");
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            result = sb.toString();
         if (  result == null  )        {
        //   Toast.makeText(getApplicationContext(), "You entered wrong values.", Toast.LENGTH_LONG).show(); 
             asyncTask.cancel(true);
            Intent  inte=new Intent(MainActivity.this, MainActivity.class);
            inte.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
            inte.addCategory(Intent.CATEGORY_HOME);
                startActivity(inte);                                
            }
        } 
        catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
                             }
        return result;
    }

I canceled the task and create a new intent in my code. You don't care them. You see Toast.makeText.. line, I tried like this one of course it gives error. How can i do this? If it isn't called in AsyncTask, how should i call?

Answer 1

doInbackground is invoked on a background thread. So you cannot update ui on a different thread other than the ui thread.

You can return the result in doInbackground Based on the result update ui in onPostExecute or use runOnUithread which is a method of activity class.

runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        // toast here
                    }
                });

Or

protected String doInBackground(Boolean... params) {
// other code
return "status"
} 
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
    Toast.makeText(getApplicationContext(),"My status is"+result,Toast.LENGTH_SHORT).show(); 
}

Edit

As suggested by @codeMagic move you startActivity also to onPostExecute. Also you do not want to cancel the asynctask run when you still have code to run