Class/Interface

描述

LoaderManager

一個與Activity和Fragment有關聯的抽象類，用於管理一個或多個Loader例項。這有助於app管理長執行操作。使用它的最顯著的例子是CursorLoader。每個Activity或Fragment只能有一個LoaderManager。而一個LoaderManager可以有多個loaders。

LoaderManager.LoaderCallbacks

提供給客戶端的一個callback介面，用於和LoaderManager進行互動。例如，你可以使用onCreateLoader() callback來建立一個新的loader。

AsyncTaskLoader

一個抽象Loader，提供一個AsyncTask進行工作。

CursorLoader

AsyncTaskLoader的子類，用於向ContentResover請求，返回一個Cursor。這個類以標準的遊標查詢方式實現了Loader協議，建立了AsyncTaskLoader，使用一個後臺執行緒來進行遊標查詢，不會阻塞app的UI。因此，使用這個loader是從ContentProvider載入非同步資料的最好的方式。

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

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);
      }
  }