Change UI crashes when called from onPostExecute

Question

I can not modify UI onPostExecute in DialogFragment

I have already read all questions about this. And this's not the same case. Believe me.

I know an AsyncTask doInBackground function has his own thread, and you must touch the view in onPreExecute and onPostExecute. And with all these things, the app is still crashing.

The exception I get is:

E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at .onPostExecute(CustomDialogFragment.java:310)     
            at android.os.AsyncTask.finish(AsyncTask.java:631)

Can't touch views from onPostExecute's AsyncTask

Here: `activity.runOnUiThread(new Runnable() { ... }`. I think `activity` is null, why don't you use `getActivity()` like below? Anyway nesting an `AsyncTask` can be dangerous, you could create memory leaks. — Xaver Kapeller, Jul 24 '14 at 07:34
You don't need `runOnUiThread` as `onPostExecute` is invoked on the ui Thread — Raghunandan, Jul 24 '14 at 07:36
Toast.makeText(getActivity().getApplicationContext(), "why onPostExecute not work", Toast.LENGTH_SHORT).show(); — Kamil Nękanowicz, Jul 24 '14 at 08:16
How does the link to the "Can't touch views..." question relate to this? Please supplement it with some explanation text. — ivan_pozdeev, Jul 24 '14 at 08:19
why? because I can't touch views in onPostExecute in DialogFragment — Kamil Nękanowicz, Jul 25 '14 at 06:32

score 0 · Answer 1 · answered Jul 24 '14 at 07:33

0

instead of activity.runOnUiThread use getActivity().runonUiThread

answered Jul 24 '14 at 07:33

Kapil Vats

5,485
1
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I did: activity = (MainActivity) getActivity(); activity.runOnUiThread(new Runnable() – Kamil Nękanowicz Jul 24 '14 at 07:36
This is a off side note but is getActivity() an instance method inside activity, that you can call from inner class? – committedandroider Jul 24 '14 at 07:41

score 0 · Answer 2 · answered Jul 24 '14 at 08:30

As @Raghunandan correctly mentioned, onPostExecute is invoked on the UI Thread so runOnUiThread is not necessary.

Change your AsyncTask to get Context in its constructor:

private class DownloadFilesTask extends AsyncTask<String,String,String> {

    private Context context;
    public DownloadFilesTask(Context context) {
            super();
            this.context = context;
    }

and use it like this:

@Override
protected void onPostExecute(String result) {
        super.onPostExecute(result);

        Toast.makeText(context, 
                      "why onPostExecute not work", Toast.LENGTH_SHORT).show();

}

Don't forget to instantiate the AsyncTask with the context:

final DownloadFilesTask downloadTask = new DownloadFilesTask(getActivity());

still, I can not modify UI onPostExecute in DialogFragment – Kamil Nękanowicz Aug 13 '14 at 12:21 — Kamil Nękanowicz, Aug 13 '14 at 12:21

score 0 · Accepted Answer · answered Nov 13 '14 at 07:43

0

The problem was much deeper than it seems.

The real problem was because I use Toast.show() and dimiss() dialog from onPostExecute. Small time delay(100ms) solves the problem

answered Nov 13 '14 at 07:43

Kamil Nękanowicz

6,254
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34
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Change UI crashes when called from onPostExecute

3 Answers3