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在activity或者fragment更加容易的异步加载数据,Loaders有如下特性:
Class/Interface | Description |
---|---|
LoaderManager | 与activity和frament关联用于管理一个或多个Loader实例的抽象类,它最常见就是和CursorLoader结合使用。 每个activity或fragment只有一个LoaderManager,但是一个LoaderManager可以操作多个loaders。 |
LoaderManager.LoaderCallbacks | 一个客户端与LoaderManager交互的回调接口,例如,你可以用onCreateLoader()回调方法来创建新的loader。 |
Loader | 一个执行异步加载数据的抽象类,这个loader的基类,典型地你可以使用CursorLoader,但是你也能实现自己的自雷。当loaders被激活,他们应该能够监控数据源的变化,然后在数据变化时发出新的结果。 |
AsyncTaskLoader | 一个提供AsyncTask去执行操作的抽象loader。 |
CursorLoader | AsyncTaskLoader的子类,它可以查询ContentResolver并返回一个Cursor,这个类用标准的方式实现了Loader协议来查询cursors,基于AsyncTaskLoader在后台线程执行cursor查询,这样不会阻塞UI。使用这个loader是一种比较好的异步加载数据的方式。 |
一般地,应用使用loaders需要包含如下信息:
通常在activity的onCreate或者fragment的onActivityCreated方法中初始化Loader:
// Prepare the loader. Either re-connect with an existing one, // or start a new one. getLoaderManager().initLoader(0, null, this);
这个initLoader方法,有两种可能:
如果你需要废弃老的数据,请使用restartLoader,如下例子,查询条件发生变化,loadre需要重启来使用改变后的查询条件:
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; }
public static class CursorLoaderListFragment extends ListFragment implements OnQueryTextListener, LoaderManager.LoaderCallbacks<Cursor> { // 用于显示列表数据的adapter SimpleCursorAdapter mAdapter; // 如果不为null,使用当前的filter 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); } }
Develop系列-API Guides-应用组件-Activities-Loaders,布布扣,bubuko.com
Develop系列-API Guides-应用组件-Activities-Loaders
标签:des android style blog http color 使用 os
原文地址:http://www.cnblogs.com/konger/p/3908754.html