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      1 page.title=Handling the Results
      2 trainingnavtop=true
      3 startpage=true
      4 
      5 @jd:body
      6 
      7 <!-- This is the training bar -->
      8 <div id="tb-wrapper">
      9   <div id="tb">
     10 <h2>This lesson teaches you to</h2>
     11 <ol>
     12   <li>
     13     <a href="#HandleResults">Handle Query Results</a>
     14   </li>
     15   <li>
     16     <a href="#HandleReset">Clear Out Old Data</a></li>
     17 </ol>
     18   </div>
     19 </div>
     20 
     21 <p>
     22     {@link android.support.v4.content.CursorLoader} returns its query results to your
     23     implementation of
     24     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished
     25     LoaderCallbacks.onLoadFinished()}, in the form of a {@link android.database.Cursor}. In the
     26     callback, you can update your data display, do further processing on the
     27     {@link android.database.Cursor} data, and so forth.
     28 </p>
     29 <p>
     30     When the loader framework detects changes to data associated with the query,
     31     it resets the {@link android.support.v4.content.CursorLoader}, closes the current
     32     {@link android.database.Cursor}, and then invokes your implementation of
     33     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}.
     34     Use this callback to delete references to the current {@link android.database.Cursor}; when the
     35     loader framework destroys the {@link android.database.Cursor}, you won't have outstanding
     36     references that cause memory leaks.
     37 </p>
     38 <h2 id="HandleFinished">Handle Query Results</h2>
     39 <p>
     40     The following two snippets are an example of displaying the results of a query, using a
     41     {@link android.widget.ListView} backed by a
     42     {@link android.support.v4.widget.SimpleCursorAdapter}.
     43 </p>
     44 <p>
     45     The first snippet shows the {@link android.widget.ListView} and
     46     {@link android.support.v4.widget.SimpleCursorAdapter}:
     47 </p>
     48 <pre>
     49 // Gets a handle to the Android built-in ListView widget
     50 mListView = ((ListView) findViewById(android.R.id.list));
     51 // Creates a CursorAdapter
     52 mAdapter =
     53     new SimpleCursorAdapter(
     54     this,                   // Current context
     55     R.layout.logitem,       // View for each item in the list
     56     null,                   // Don't provide the cursor yet
     57     FROM_COLUMNS,           // List of cursor columns to display
     58     TO_FIELDS,              // List of TextViews in each line
     59     0                       // flags
     60 );
     61 // Links the adapter to the ListView
     62 mListView.setAdapter(mAdapter);
     63 </pre>
     64 <p>
     65     The next snippet shows an implementation of
     66     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}
     67     that moves the query results in the returned {@link android.database.Cursor} to the
     68     {@link android.support.v4.widget.SimpleCursorAdapter}. Changing the
     69     {@link android.database.Cursor} in the
     70     {@link android.support.v4.widget.SimpleCursorAdapter} triggers a refresh of the
     71     {@link android.widget.ListView} with the new data:
     72 </p>
     73 <pre>
     74 public void onLoadFinished(Loader&lt;Cursor&gt; loader, Cursor cursor)
     75 {
     76     /*
     77      * Move the results into the adapter. This
     78      * triggers the ListView to re-display.
     79      */
     80     mAdapter.swapCursor(cursor);
     81 }
     82 </pre>
     83 <h2 id="HandleReset">Handle a Loader Reset</h2>
     84 <p>
     85     The loader framework resets the {@link android.support.v4.content.CursorLoader} whenever the
     86     {@link android.database.Cursor} becomes invalid. This usually occurs because the data associated
     87     with the {@link android.database.Cursor} has changed. Before re-running the query,
     88     the framework calls your implementation of
     89     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}. In
     90     this callback, make sure to prevent memory leaks by deleting all references to the current
     91     {@link android.database.Cursor}. Once you return from
     92     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()},
     93     the loader framework re-runs the query.
     94 </p>
     95 <p>
     96     For example:
     97 </p>
     98 <pre>
     99 public void onLoaderReset(Loader&lt;Cursor&gt; loader)
    100 {
    101     // Remove the reference to the current Cursor
    102     mAdapter.swapCursor(null);
    103 }
    104 </pre>
    105