LoaderManager使用详解（一）---Android中的Loaders机制

public boolean onQueryTextChanged(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.
mCurFilter = !TextUtils.isEmpty(newText) ? newText : null;
getLoaderManager().restartLoader(0, null, this);
return true;
}

// If non-null, this is the current filter the user has provided.
String mCurFilter;
...
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");
}

// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;
...

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);
}

// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;
...

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);
}

public static class CursorLoaderListFragment extends ListFragment
implements OnQueryTextListener, LoaderManager.LoaderCallbacks<Cursor> {

// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;

// 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);

// Prepare the loader.  Either re-connect with an existing one,
// or start a new one.
getLoaderManager().initLoader(0, null, this);
}

@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);
SearchView sv = new SearchView(getActivity());
sv.setOnQueryTextListener(this);
item.setActionView(sv);
}

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.
mCurFilter = !TextUtils.isEmpty(newText) ? newText : null;
getLoaderManager().restartLoader(0, null, this);
return true;
}

@Override public boolean onQueryTextSubmit(String query) {
// Don't care about this.
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);
}

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);
}
}