Loader和Fragment使用示例代码

程序语言 Java
1

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);
    }
}

}