使用CursorLoader异步加载数据

Android 3.0引入了CursorLoader实现异步加载数据，为了避免同步查询数据库时阻塞UI线程的问题。在API 11之前可以通过下载支持库，来使之前的系统支持此功能。

下面是一个例子：

public class ListViewLoader extends ListActivity
  implements LoaderManager.LoaderCallbacks<Cursor> {

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

 // These are the Contacts rows that we will retrieve
 static final String[] PROJECTION = new String[] {ContactsContract.Data._ID,
   ContactsContract.Data.DISPLAY_NAME};

 // This is the select criteria
 static final String SELECTION = "((" + 
   ContactsContract.Data.DISPLAY_NAME + " NOTNULL) AND (" +
   ContactsContract.Data.DISPLAY_NAME + " != '' ))";

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

  // Create a progress bar to display while the list loads
  ProgressBar progressBar = new ProgressBar(this);
  progressBar.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
    LayoutParams.WRAP_CONTENT, Gravity.CENTER));
  progressBar.setIndeterminate(true);
  getListView().setEmptyView(progressBar);

  // Must add the progress bar to the root of the layout
  ViewGroup root = (ViewGroup) findViewById(android.R.id.content);
  root.addView(progressBar);

  // For the cursor adapter, specify which columns go into which views
  String[] fromColumns = {ContactsContract.Data.DISPLAY_NAME};
  int[] toViews = {android.R.id.text1}; // The TextView in simple_list_item_1

  // Create an empty adapter we will use to display the loaded data.
  // We pass null for the cursor, then update it in onLoadFinished()
  mAdapter = new SimpleCursorAdapter(this, 
    android.R.layout.simple_list_item_1, null,
    fromColumns, toViews, 0);
  setListAdapter(mAdapter);

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

 // Called when a new Loader needs to be created
 public Loader<Cursor> onCreateLoader(int id, Bundle args) {
  // Now create and return a CursorLoader that will take care of
  // creating a Cursor for the data being displayed.
  return new CursorLoader(this, ContactsContract.Data.CONTENT_URI,
    PROJECTION, SELECTION, null, null);
 }

 // Called when a previously created loader has finished loading
 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);
 }

 // Called when a previously created loader is reset, making the data unavailable
 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);
 }

 @Override 
 public void onListItemClick(ListView l, View v, int position, long id) {
  // Do something when a list item is clicked
 }
}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持自由互联。