Android Guides | Samples

Android.App.LoaderManager Class

Interface associated with an Activity or Fragment for managing one or more Loader instances associated with it.

See Also: LoaderManager

Syntax

[Android.Runtime.Register("android/app/LoaderManager", DoNotGenerateAcw=true)]
public abstract class LoaderManager : Object

Remarks

Interface associated with an Activity or Fragment for managing one or more 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 CursorLoader, however applications are free to write their own loaders for loading other types of data. While the LoaderManager API was introduced in Build+VERSION_CODES.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 Fragment that displays a ListView containing the results of a query against the contacts content provider. It uses a 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);
    }
}

Developer Guides

For more information about using loaders, read the Loaders developer guide.

[Android Documentation]

Requirements

Namespace: Android.App
Assembly: Mono.Android (in Mono.Android.dll)
Assembly Versions: 0.0.0.0
Since: Added in API level 11

The members of Android.App.LoaderManager are listed below.

See Also: Object

Public Constructors

Protected Constructors

A constructor used when creating managed representations of JNI objects; called by the runtime.

Protected Properties

[read-only]
override
ThresholdClassIntPtr. This API supports the Mono for Android infrastructure and is not intended to be used directly from your code.
[read-only]
override
ThresholdTypeType. This API supports the Mono for Android infrastructure and is not intended to be used directly from your code.

Public Methods

abstract
DestroyLoader(Int32)
Stops and removes the loader with the given ID.
abstract
Dump(String, FileDescriptor, PrintWriter, String[])
Print the LoaderManager's state into the given stream.
static
EnableDebugLogging(Boolean)
Control whether the framework's internal loader manager debugging logs are turned on.
abstract
GetLoader(Int32) : Loader
Return the Loader with the given id or null if no matching Loader is found.
abstract
InitLoader(Int32, Bundle, LoaderManager+ILoaderCallbacks) : Loader
abstract
RestartLoader(Int32, Bundle, LoaderManager+ILoaderCallbacks) : Loader