Loader和Fragment使用示例代码

Loader和Fragment都是Android 3.0的新特性，有关Fragment相关的内容Android开发网已经用了多个篇幅介绍，而Loader相关的大家可以通过 LoaderManager - Android 3.0新特性 一文了解Loader的作用和结构，下面就以一个简单的工程示例代码了解下Loader。

public class FragmentListCursorLoader extends Activity {

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

        FragmentManager fm = getFragmentManager(); //获取FragmentManager这个服务实例

        if (fm.findFragmentById(android.R.id.content) == null) { //这个资源是android内部的布局，注意是android.R
            CursorLoaderListFragment list = new CursorLoaderListFragment();
            fm.beginTransaction().add(android.R.id.content, list).commit();
        }
    }

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

        SimpleCursorAdapter mAdapter; //这里使用简单cursor适配器绑定数据库

        String mCurFilter;

        @Override public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            setEmptyText("No phone numbers");

            setHasOptionsMenu(true); //显示actionbar，如果不明白看android123以前的文章

            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);

            getLoaderManager().initLoader(0, null, this);
        }

        @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
            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) {
            mCurFilter = !TextUtils.isEmpty(newText) ? newText : null;
            getLoaderManager().restartLoader(0, null, this);
            return true;
        }

        @Override public boolean onQueryTextSubmit(String query) {
            return true;
        }

        @Override public void onListItemClick(ListView l, View v, int position, long id) {
            Log.i("FragmentComplexList", "Item clicked: " + id);
        }

        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) { //这里的处理是异步的
            Uri baseUri;
            if (mCurFilter != null) {
                baseUri = Uri.withAppendedPath(Contacts.CONTENT_FILTER_URI,
                        Uri.encode(mCurFilter));
            } else {
                baseUri = Contacts.CONTENT_URI;
            }

            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) {
            mAdapter.swapCursor(data); //处理完成
        }

        public void onLoaderReset(Loader<Cursor> loader) {
            mAdapter.swapCursor(null);
        }
    }
}