See Also: LoaderManager Members
Interface associated with an Android.App.Activity or Android.App.Fragment for managing one or more Android.Content.Loader instances associated with it. This helps an application manage longer-running operations in conjunction with the Activity or Fragment lifecycle; the most common use of this is with a Android.Content.CursorLoader, however applications are free to write their own loaders for loading other types of data. While the LoaderManager API was introduced in NoType:android/os/Build$VERSION_CODES;Href=../../../reference/android/os/Build.VERSION_CODES.html#HONEYCOMB, a version of the API at is also available for use on older platforms through NoType:android/support/v4/app/FragmentActivity;Href=../../../reference/android/support/v4/app/FragmentActivity.html. See the blog post for more details.
As an example, here is the full implementation of a Android.App.Fragment that displays a Android.Widget.ListView containing the results of a query against the contacts content provider. It uses a Android.Content.CursorLoader to manage the query on the provider.
java Example
public static class CursorLoaderListFragment extends ListFragment implements OnQueryTextListener, OnCloseListener, LoaderManager.LoaderCallbacks<Cursor> { // This is the Adapter being used to display the list's data. SimpleCursorAdapter mAdapter; // The SearchView for doing filtering. SearchView mSearchView; // If non-null, this is the current filter the user has provided. String mCurFilter; @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); // Give some text to display if there is no data. In a real // application this would come from a resource. setEmptyText("No phone numbers"); // We have a menu item to show in action bar. setHasOptionsMenu(true); // Create an empty adapter we will use to display the loaded data. mAdapter = new SimpleCursorAdapter(getActivity(), android.R.layout.simple_list_item_2, null, new String[] { Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS }, new int[] { android.R.id.text1, android.R.id.text2 }, 0); setListAdapter(mAdapter); // Start out with a progress indicator. setListShown(false); // Prepare the loader. Either re-connect with an existing one, // or start a new one. getLoaderManager().initLoader(0, null, this); } public static class MySearchView extends SearchView { public MySearchView(Context context) { super(context); } // The normal SearchView doesn't clear its search text when // collapsed, so we will do this for it. @Override public void onActionViewCollapsed() { setQuery("", false); super.onActionViewCollapsed(); } } @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { // Place an action bar item for searching. MenuItem item = menu.add("Search"); item.setIcon(android.R.drawable.ic_menu_search); item.setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM | MenuItem.SHOW_AS_ACTION_COLLAPSE_ACTION_VIEW); mSearchView = new MySearchView(getActivity()); mSearchView.setOnQueryTextListener(this); mSearchView.setOnCloseListener(this); mSearchView.setIconifiedByDefault(true); item.setActionView(mSearchView); } public boolean onQueryTextChange(String newText) { // Called when the action bar search text has changed. Update // the search filter, and restart the loader to do a new query // with this filter. String newFilter = !TextUtils.isEmpty(newText) ? newText : null; // Don't do anything if the filter hasn't actually changed. // Prevents restarting the loader when restoring state. if (mCurFilter == null && newFilter == null) { return true; } if (mCurFilter != null && mCurFilter.equals(newFilter)) { return true; } mCurFilter = newFilter; getLoaderManager().restartLoader(0, null, this); return true; } @Override public boolean onQueryTextSubmit(String query) { // Don't care about this. return true; } @Override public boolean onClose() { if (!TextUtils.isEmpty(mSearchView.getQuery())) { mSearchView.setQuery(null, true); } return true; } @Override public void onListItemClick(ListView l, View v, int position, long id) { // Insert desired behavior here. Log.i("FragmentComplexList", "Item clicked: " + id); } // These are the Contacts rows that we will retrieve. static final String[] CONTACTS_SUMMARY_PROJECTION = new String[] { Contacts._ID, Contacts.DISPLAY_NAME, Contacts.CONTACT_STATUS, Contacts.CONTACT_PRESENCE, Contacts.PHOTO_ID, Contacts.LOOKUP_KEY, }; public Loader<Cursor> onCreateLoader(int id, Bundle args) { // This is called when a new Loader needs to be created. This // sample only has one Loader, so we don't care about the ID. // First, pick the base URI to use depending on whether we are // currently filtering. Uri baseUri; if (mCurFilter != null) { baseUri = Uri.withAppendedPath(Contacts.CONTENT_FILTER_URI, Uri.encode(mCurFilter)); } else { baseUri = Contacts.CONTENT_URI; } // Now create and return a CursorLoader that will take care of // creating a Cursor for the data being displayed. String select = "((" + Contacts.DISPLAY_NAME + " NOTNULL) AND (" + Contacts.HAS_PHONE_NUMBER + "=1) AND (" + Contacts.DISPLAY_NAME + " != '' ))"; return new CursorLoader(getActivity(), baseUri, CONTACTS_SUMMARY_PROJECTION, select, null, Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC"); } public void onLoadFinished(Loader<Cursor> loader, Cursor data) { // Swap the new cursor in. (The framework will take care of closing the // old cursor once we return.) mAdapter.swapCursor(data); // The list should now be shown. if (isResumed()) { setListShown(true); } else { setListShownNoAnimation(true); } } public void onLoaderReset(Loader<Cursor> loader) { // This is called when the last Cursor provided to onLoadFinished() // above is about to be closed. We need to make sure we are no // longer using it. mAdapter.swapCursor(null); } }
For more information about using loaders, read the Loaders developer guide.