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android – AsyncTask – after execution, how to update view?

Posted by: admin May 14, 2020 Leave a comment

Questions:

In the onCreate() event of an Activity, I have started an AsyncTask to retrieve Product data from a database. After this has been completed successfully, how can I update the display?

Metacode:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.venueviewbasic);
            (..)
    new GetProductDetails().execute();

class GetProductDetails extends AsyncTask<String, String, String> {

    protected String doInBackground(String... params) {

        // updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {
                // Check for success tag
                int success;
                try {
                    // Building Parameters
                    List<NameValuePair> params = new ArrayList<NameValuePair>();
                    params.add(new BasicNameValuePair("id", vid));
        (.. retrieve and parse data and set new textview contents ..)

The textviews etc. don’t get updated however.

How to&Answers:

If you want to update the view from async after complete process in then
you can use

protected void onPostExecute(String result)
    {
        textView.setText(result);
    }

But if you want to update data while running background process then use.
For ex…

protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));<------
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {  <-------
         setProgressPercent(progress[0]);
     }

for more detail see this link
Hope this will help you…!

Answer:

I am guessing the question is more about how to get hold of the UI View if the asyncTask is in a separate file .

In that case you have to pass the context to the Async task and use that to get the view.

class MyAsyncTask extends AsyncTask<URL, Integer, Long> {

    Activity mActivity;

    public MyAsyncTask(Activity activity) {
       mActivity = ativity;
    }

And then in your onPostExecute use

int id = mActivity.findViewById(...);

Remember you cannot update the View from “doInBackground” since its not the UI thread.

Answer:

In your AsyncTask class, add a onPostExecute method. This method executes on the UI thread and can update any UI component.

class GetProductDetails extends AsyncTask<...> 
{
    ...
    private TextView textView;
    ...
    protected void onPostExecute(String result)
    {
        textView.setText(result);
    }
}

(The result parameter is the value returned from the doInBackground method of your class.)