StateSavingArrayAdapter.java

/**
 * <p>
 * An {@code ArrayAdapter} that also knows how to save and restore its state.
 * Basically all it does is save/restore the array of objects being managed by
 * the Adapter.
 * </p>
 * 
 * <p>
 * Note that this only saves the items and not things like checked item
 * positions. Those belong to the {@link ListView} itself. Consider using
 * {@link ListView#onSaveInstanceState()} and
 * {@link ListView#onRestoreInstanceState(Parcelable)} for this purpose.
 * </p>
 * 
 * 
 * @author Kiran Rao
 * 
 * @param <T>
 *          The type of objects managed by this Adapter. Note that it must be a
 *          Parcelable.
 */
public class StateSavingArrayAdapter<T extends Parcelable> extends
    ArrayAdapter<T> {

  private static final String KEY_ADAPTER_STATE = "StateSavingArrayAdapter.KEY_ADAPTER_STATE";

  /**
   * Saves the instance state of this {@link ArrayAdapter}. It saves the array
   * of currently managed by this adapter
   * 
   * @param outState
   *          The bundle into which the state is saved
   */
  public void onSaveInstanceState(Bundle outState) {
    outState.putParcelableArrayList(KEY_ADAPTER_STATE, getAllItems());
  }

  /**
   * Restore the instance state of the {@link ArrayAdapter}. It re-initializes
   * the array of objects being managed by this adapter with the state retrieved
   * from {@code savedInstanceState}
   * 
   * @param savedInstanceState
   *          The bundle containing the previously saved state
   */
  public void onRestoreInstanceState(Bundle savedInstanceState) {
    if (savedInstanceState.containsKey(KEY_ADAPTER_STATE)) {
      ArrayList<T> objects = savedInstanceState
          .getParcelableArrayList(KEY_ADAPTER_STATE);
      setItems(objects);
    }
  }
  
  /**
   * Gets all the items in this adapter as an {@code ArrayList}
   */
  public ArrayList<T> getAllItems(){
    ArrayList<T> objects = new ArrayList<T>(getCount());
    for (int i = 0; i < getCount(); i++) {
      objects.add(getItem(i));
    }
    return objects;
  }
  
  /*
   * Replaces the items in the adapter with those in this list
   * @param items The items to set into the adapter.
   */
  public void setItems(ArrayList<T> items){
    clear();
    addAll(items);
  }

  /* Constructors and other boilerplate */

  public StateSavingArrayAdapter(Context context, int resource) {
    super(context, resource);
  }

  public StateSavingArrayAdapter(Context context, int resource,
      int textViewResourceId) {
    super(context, resource, textViewResourceId);
  }

  public StateSavingArrayAdapter(Context context, int resource, T[] objects) {
    super(context, resource, objects);
  }

  public StateSavingArrayAdapter(Context context, int resource, List<T> objects) {
    super(context, resource, objects);
  }

  public StateSavingArrayAdapter(Context context, int resource,
      int textViewResourceId, T[] objects) {
    super(context, resource, textViewResourceId, objects);
  }

  public StateSavingArrayAdapter(Context context, int resource,
      int textViewResourceId, List<T> objects) {
    super(context, resource, textViewResourceId, objects);
  }

}

StateSavingMainActivity.java

/*
 * Illustration of how to use the StateSavingArrayAdapter.
 * 
 * First, have your custom Adapter extend StateSavingArrayAdapter instead of ArrayAdapter.
 * Then, call the appropriate methods in onSaveInstanceState/ onCreate as illustrated here.
 * 
 * This example also illustrates how you would save the ListView state itself so that your checked items are remembered.
 */

public class StateSavingMainActivity extends Activity {

  private UserAdapter mAdapter;
  private ListView mListView;
  private static final String KEY_LIST_VIEW_STATE = "KEY_LIST_VIEW_STATE";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    /* Create the mAdapter instance here. For example, mAdapter = new UserAdapter(this); */
    /* Then, restore the adapter state as follows */
    if (savedInstanceState != null) {
      mAdapter.onRestoreInstanceState(savedInstanceState);
    }

    mListView = (ListView) findViewById(android.R.id.list);
    if (savedInstanceState != null
        && savedInstanceState.containsKey(KEY_LIST_VIEW_STATE)) {
      mListView.onRestoreInstanceState(savedInstanceState
          .getParcelable(KEY_LIST_VIEW_STATE));
    }
    mListView.setAdapter(mAdapter);

  }

  @Override
  protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    mAdapter.onSaveInstanceState(outState);
    outState
        .putParcelable(KEY_LIST_VIEW_STATE, mListView.onSaveInstanceState());
  }

  private class UserAdapter extends StateSavingArrayAdapter<User> {
    /* Add appropriate constructors */

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      /*
       * Inflate your XML and return the view here
       */
      return super.getView(position, convertView, parent);
    }
  }

}