Question

I’ve got an activity with a search field with a “near current location” checkbox and a listview to show the results. I’m now in the life cycle of the activity, implementing the onSaveInstanceState and onRestoreInstanceState methods. When the activity is destroyed and I get back to it, the listview with the results has disappeared, but the text in the search box and the checkbox state are restored, while I haven’t saved anything in onSaveInstanceState. Why? What is saved “automatically” and what do I need to save in onSaveInstanceState?

public class Atable extends Activity {
    private EditText mSearch;
    private static final int ACTIVITY_EDIT=0;
    private Button mSearchButton;
    private TextView mNoresults;
    private TextView mytext;
    private ListView lv;
    private CheckBox checkBox;
    private LocationManager locationManager;    


    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);        

        setContentView(R.layout.main);

        lv= (ListView)findViewById(R.id.listview);

        mNoresults = (TextView) findViewById(R.id.noresults);  
        mNoresults.setVisibility(View.GONE);

        mSearchButton = (Button)this.findViewById(R.id.button);
        checkBox = (CheckBox) findViewById(R.id.local_check);        

        locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        final Criteria criteria = new Criteria();
        criteria.setAccuracy(Criteria.ACCURACY_FINE);

        mSearchButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                mNoresults.setVisibility(View.GONE);
                mSearch = (EditText) findViewById(R.id.search);  
                String tmp_str = mSearch.getText().toString().replace(" ","+");           

                HttpClient httpclient = new DefaultHttpClient();    

                // Prepare a request object
                String url = "http://www.atable.org/getRestaurantByQuery/?query=" + tmp_str;              

                if (checkBox.isChecked()) {

                    //get location
                    String provider = locationManager.getBestProvider(criteria, true);                
                    Location location = locationManager.getLastKnownLocation(provider);

                    if (location!=null) {

                        String lat = String.valueOf(location.getLatitude());
                        String lng = String.valueOf(location.getLongitude());

                        url += "&lat="+lat+"&lng="+lng;                   
                    }
                }

                HttpGet httpget = new HttpGet(url); 

                // Execute the request
                HttpResponse response;
                try {
                    response = httpclient.execute(httpget);
                    HttpEntity entity = response.getEntity();

                    if (entity != null) {

                        InputStream instream = entity.getContent();

                        Reader r = new InputStreamReader(instream);                      

                        Gson gson = new Gson();
                        final RestaurantList restaurantList = gson.fromJson(r, RestaurantList.class);

                        int nResults = restaurantList.getSize();

                        if (nResults>0) {

                            lv.setVisibility(View.VISIBLE);

                            lv.setAdapter( new ArrayAdapter<String>(Atable.this ,android.R.layout.simple_list_item_1,restaurantList.getRestaurantNames()));

                            lv.setOnItemClickListener(new OnItemClickListener() {

                                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                                    Intent intent = new Intent(Atable.this, RestaurantDescription.class);
                                    Restaurant tmp_resto = restaurantList.getRestaurant((int)id);

                                    String tmp_categories = tmp_resto.getCategories().get(0);
                                    for (int i=1; i<tmp_resto.getCategories().size(); i++) {
                                        tmp_categories+=", "+tmp_resto.getCategories().get(i);
                                    }

                                    String address = tmp_resto.getStreet()+", "+tmp_resto.getStreetNumber()+"\n"+tmp_resto.getCity()+
                                                    " "+tmp_resto.getPostalCode()+"\n"+tmp_resto.getCountry();

                                    intent.putExtra("name", tmp_resto.getName());
                                    intent.putExtra("address", address);                                
                                    intent.putExtra("rating", tmp_resto.getRating());
                                    intent.putExtra("price_range", tmp_resto.getPriceRange());
                                    intent.putExtra("categories", tmp_categories);
                                    intent.putExtra("latitude", tmp_resto.getLatitude());
                                    intent.putExtra("longitude", tmp_resto.getLongitude());
                                    startActivityForResult(intent, ACTIVITY_EDIT);
                                }
                            });

                        }

                        else {
                            lv.setVisibility(View.GONE);
                            mNoresults.setVisibility(View.VISIBLE);
                        }

                        //Closing the input stream will trigger connection release
                        instream.close();
                    }   


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

    }

    //Start a location listener
    LocationListener onLocationChange=new LocationListener() {
        public void onLocationChanged(Location loc) {
            //sets and displays the lat/long when a location is provided
            /*String latlong = "Lat: " + loc.getLatitude() + " Long: " + loc.getLongitude();   
            mytext.setText(latlong);*/
        }

        public void onProviderDisabled(String provider) {
        // required for interface, not used
        }

        public void onProviderEnabled(String provider) {
        // required for interface, not used
        }

        public void onStatusChanged(String provider, int status,
        Bundle extras) {
        // required for interface, not used
        }
    };

    //pauses listener while app is inactive
    @Override
    public void onPause() {
        super.onPause();
        locationManager.removeUpdates(onLocationChange);
    }

    //reactivates listener when app is resumed
    @Override
    public void onResume() {
        super.onResume();
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,0,0,onLocationChange);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Toast.makeText(this, "Activity is getting killed", Toast.LENGTH_LONG).show();
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {      
        Toast.makeText(this, "onRestoreInstanceState", Toast.LENGTH_LONG).show();
        super.onRestoreInstanceState(savedInstanceState);
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {       
        Toast.makeText(this, "onSaveInstanceState", Toast.LENGTH_LONG).show();
        super.onSaveInstanceState(outState);
    }

}

Answer 1

First, don’t perform network requests on your UI thread. You’ll make your UI unresponsive for the duration of the operation and risk triggering ANRs. Consider using AsyncTask to query your server.

By default Activities save and restore their view hierarchy state. Each View‘s implementation is responsible for deciding what parts of its state should be saved and restored. ListView is a special case as usual.

ListView does save state about current list position and item selection, but all of that is useless without an adapter. If you set an adapter before the saved view hierarchy state is restored in Activity#onRestoreInstanceState, ListView will attempt to re-sync its view state with the data.

When onSaveInstanceState is called and you have result data available, you can write your saved search results into the Bundle you’re given.

In onCreate, check to see if the supplied Bundle is not null and if your data is present within it from a previous query. If it is, read it back out. Use it to construct a new adapter and call setAdapter on your ListView. ListView should take it from there.