在AsyncTask Android应用的PostExecute方法中显示Toast消息

Question

Ok, so I have an AsyncTask that is adding items to a ListView . On PreExecute, I am displaying a message "Starting" and on PostExecute I am displaying "Done". The "Starting" message is displayed but for some reason, when the listing is done, the "Done" message is NOT displayed. Does anyone have any ideas on why the message is not displaying in the PostExecute section of this Task? Thank you

Code:

class FillLocations extends AsyncTask<Integer, Void, Void> {

    public FillLocations() {

    }

    protected void onPreExecute() {
        Toast.makeText(getApplicationContext(), "Starting",
                Toast.LENGTH_LONG).show();
    }

    // Decode image in background.
    @Override
    protected Void doInBackground(Integer... params) {

        String result = "";
        InputStream isr = null;
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("http://myscript/"); // YOUR
                                                                                // PHP
                                                                                // SCRIPT
                                                                                // ADDRESS
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            isr = entity.getContent();
            // resultView.setText("connected");
        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection " + e.toString());
        }
        // convert response to string
        try {
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(isr, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            isr.close();

            result = sb.toString();
        } catch (Exception e) {
            Log.e("log_tag", "Error  converting result " + e.toString());
        }

        // parse json data
        try {
            JSONArray jArray = new JSONArray(result);

            for (int i = 0; i < jArray.length(); i++) {
                final JSONObject json = jArray.getJSONObject(i);

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {

                        try {

                            BitmapWorkerTask myTask = new BitmapWorkerTask(
                                    json.getInt("ID"), json);
                            myTask.execute();

                        } catch (JSONException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }

                    }
                });

            }

        } catch (Exception e) {
            // TODO: handle exception
            Log.e("log_tag", "Error Parsing Data " + e.toString());
        }
        return null;

    }

    protected void onPostExecute() {
        Toast.makeText(getApplicationContext(), "Done", Toast.LENGTH_LONG)
                .show();

    }
}

Answer 1

You need to appropriately implement onPostExecute

@Override
protected void onPostExecute(Void void){
      // Do what you want to do, for example, your toast:
      Toast.makeText(getApplicationContext(), "Done", Toast.LENGTH_LONG)
            .show();
}

-Notes on General Practice-

Your AsyncTask doesn't need a constructor, so you can remove

public FillLocations(){
}

And you should declare your class visibility (unless you want it set to the default visibility which is the package), so make it something like

private class FillLocations extends AsyncTask<Integer, Void, Void>{
    // Your Stuff
}

Answer 2

onPostExecute takes a parameter as shown here .

Personally, I would do something like this, to tell the user that something went wrong, in case some exception is thrown. I never liked letting errors go to nirvana.

protected String doInBackground(Integer... params) {
...
}

and

protected void onPostExecute(String msg) {
    Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG)
            .show();

}

(Also, in the documentation, no @Override is used.)