Fetch AutoCompleteTextView suggestions from service in separate thread

Question

For my AutoCompleteTextView I need to fetch the data from a webservice. As it can take a little time I do not want UI thread to be not responsive, so I need somehow to fetch the data in a separate thread. For example, while fetching data from SQLite DB, it is very easy done with CursorAdapter method - runQueryOnBackgroundThread. I was looking around to other adapters like ArrayAdapter, BaseAdapter, but could not find anything similar...

Is there an easy way how to achieve this? I cannot simply use ArrayAdapter directly, as the suggestions list is dynamic - I always fetch the suggestions list depending on user input, so it cannot be pre-fetched and cached for further use...

If someone could give some tips or examples on this topic - would be great!

Answer 1

With the approach above, i also had those problems when typing very fast. I guess it´s because the filtering of the results is done asynchronously by the filter class, so there can be problems when modifying the ArrayList of the Adapter in the ui thread while filtering is done.

http://developer.android.com/reference/android/widget/Filter.html

However with following approach everything worked fine.

public class MyActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        MyAdapter myAdapter = new MyAdapter(this, android.R.layout.simple_dropdown_item_1line);

        AutoCompleteTextView acTextView = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
        acTextView.setAdapter(myAdapter);
    }
}

public class MyAdapter extends ArrayAdapter<MyObject> {
    private Filter mFilter;

    private List<MyObject> mSubData = new ArrayList<MyObject>();
    static int counter=0;

    public MyAdapter(Context context, int textViewResourceId) {
      super(context, textViewResourceId);
      setNotifyOnChange(false);

      mFilter = new Filter() {
        private int c = ++counter;
        private List<MyObject> mData = new ArrayList<MyObject>();

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
          // This method is called in a worker thread
          mData.clear();

          FilterResults filterResults = new FilterResults();
          if(constraint != null) {
            try {
              // Here is the method (synchronous) that fetches the data
              // from the server      
              URL url = new URL("...");
              URLConnection conn = url.openConnection();
              BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
              String line = "";

              while ((line = rd.readLine()) != null) {
                      mData.add(new MyObject(line));
              }
            }
            catch(Exception e) {
            }

            filterResults.values = mData;
            filterResults.count = mData.size();
          }
          return filterResults;
        }

        @SuppressWarnings("unchecked")
        @Override
        protected void publishResults(CharSequence contraint, FilterResults results) {
          if(c == counter) {
            mSubData.clear();
              if(results != null && results.count > 0) {
                ArrayList<MyObject> objects = (ArrayList<MyObject>)results.values;
                for (MyObject v : objects)
                  mSubData.add(v);

                notifyDataSetChanged();
              }
              else {
                notifyDataSetInvalidated();
              }
          }
        }
    };
  }

  @Override
  public int getCount() {
    return mSubData.size();
  }

  @Override
  public MyObject getItem(int index) {
    return mSubData.get(index);
  }

  @Override
  public Filter getFilter() {
    return mFilter;
  }
}