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
}
}

来源：https://blog.csdn.net/zzqLivecn/article/details/7896297