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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">Delete Old Cursor References</a></li>
     17 </ol>
     18 
     19 <h2>Try it out</h2>
     20 <div class="download-box">
     21     <a href="{@docRoot}shareables/training/ThreadSample.zip" class="button">Download the sample</a>
     22     <p class="filename">ThreadSample.zip</p>
     23 </div>
     24 
     25   </div>
     26 </div>
     27 
     28 <p>
     29     As shown in the previous lesson, you should begin loading your data with a
     30     {@link android.support.v4.content.CursorLoader} in your implementation of
     31     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onCreateLoader
     32     onCreateLoader()}. The loader then provides the query results to your
     33     {@link android.app.Activity} or {@link android.support.v4.app.FragmentActivity} in your
     34     implementation of {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished
     35     LoaderCallbacks.onLoadFinished()}. One of the incoming arguments to this method is a
     36     {@link android.database.Cursor} containing the query results. You can use this object to
     37     update your data display or do further processing.
     38 </p>
     39 <p>
     40     Besides
     41     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onCreateLoader onCreateLoader()} and
     42     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()},
     43     you also have to implement
     44     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}.
     45     This method is invoked when {@link android.support.v4.content.CursorLoader} detects
     46     that data associated with the {@link android.database.Cursor} has changed. When the
     47     data changes, the framework also re-runs the current query.
     48 </p>
     49 <h2 id="HandleResults">Handle Query Results</h2>
     50 <p>
     51     To display {@link android.database.Cursor} data returned by
     52     {@link android.support.v4.content.CursorLoader}, use a
     53     {@link android.view.View} class that implements {@link android.widget.AdapterView} and
     54     provide the view with an adapter that implements
     55     {@link android.support.v4.widget.CursorAdapter}. The system then automatically moves data from
     56     the {@link android.database.Cursor} to the view.
     57 </p>
     58 <p>
     59     You can set up the linkage between the view and adapter before you have any data to display,
     60     and then move a {@link android.database.Cursor} into the adapter in the
     61     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}
     62     method. As soon as you move the {@link android.database.Cursor} into the adapter, the
     63     system automatically updates the view. This also happens if you change the contents of the
     64     {@link android.database.Cursor}.
     65 </p>
     66 <p>
     67     For example:
     68 </p>
     69 <pre>
     70 public String[] mFromColumns = {
     71     DataProviderContract.IMAGE_PICTURENAME_COLUMN
     72 };
     73 public int[] mToFields = {
     74     R.id.PictureName
     75 };
     76 // Gets a handle to a List View
     77 ListView mListView = (ListView) findViewById(R.id.dataList);
     78 /*
     79  * Defines a SimpleCursorAdapter for the ListView
     80  *
     81  */
     82 SimpleCursorAdapter mAdapter =
     83     new SimpleCursorAdapter(
     84             this,                // Current context
     85             R.layout.list_item,  // Layout for a single row
     86             null,                // No Cursor yet
     87             mFromColumns,        // Cursor columns to use
     88             mToFields,           // Layout fields to use
     89             0                    // No flags
     90     );
     91 // Sets the adapter for the view
     92 mListView.setAdapter(mAdapter);
     93 ...
     94 /*
     95  * Defines the callback that {@link android.support.v4.content.CursorLoader} calls
     96  * when it's finished its query
     97  */
     98 &#64;Override
     99 public void onLoadFinished(Loader&lt;Cursor&gt; loader, Cursor cursor) {
    100     ...
    101     /*
    102      * Moves the query results into the adapter, causing the
    103      * ListView fronting this adapter to re-display
    104      */
    105     mAdapter.changeCursor(cursor);
    106 }
    107 </pre>
    108 <h2 id="HandleReset">Delete Old Cursor References</h2>
    109 <p>
    110     The {@link android.support.v4.content.CursorLoader} is reset whenever its
    111     {@link android.database.Cursor} becomes invalid. This usually occurs because the data associated
    112     with the {@link android.database.Cursor} has changed. Before re-running the query,
    113     the framework calls your implementation of
    114     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}. In
    115     this callback, you should delete all references to the current {@link android.database.Cursor}
    116     in order to prevent memory leaks. Once
    117     {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}
    118     finishes, {@link android.support.v4.content.CursorLoader} re-runs its query.
    119 </p>
    120 <p>
    121     For example:
    122 </p>
    123 <pre>
    124 /*
    125  * Invoked when the CursorLoader is being reset. For example, this is
    126  * called if the data in the provider changes and the Cursor becomes stale.
    127  */
    128 &#64;Override
    129 public void onLoaderReset(Loader&lt;Cursor&gt; loader) {
    130     
    131     /*
    132      * Clears out the adapter's reference to the Cursor.
    133      * This prevents memory leaks.
    134      */
    135     mAdapter.changeCursor(null);
    136 }
    137 </pre>
    138