android_frameworks_base/docs/html/training/contacts-provider/retrieve-details.jd

page.title=Retrieving Details for a Contact

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@jd:body

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<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#RetrieveAll">Retrieve All Details for a Contact</a></li>
  <li><a href="#RetrieveSpecific">Retrieve Specific Details for a Contact</a></li>
</ol>

<!-- other docs (NOT javadocs) -->
<h2>You should also read</h2>
<ul>
    <li>
        <a href="{@docRoot}guide/topics/providers/content-provider-basics.html">
        Content Provider Basics</a>
    </li>
    <li>
        <a href="{@docRoot}guide/topics/providers/contacts-provider.html">
        Contacts Provider</a>
    </li>
    <li>
        <a href="{@docRoot}guide/components/loaders.html">Loaders</a>
</ul>

<h2>Try it out</h2>

<div class="download-box">
    <a href="http://developer.android.com/shareables/training/ContactsList.zip" class="button">
    Download the sample
    </a>
 <p class="filename">ContactsList.zip</p>
</div>

</div>
</div>
<p>
    This lesson shows how to retrieve detail data for a contact, such as email addresses, phone
    numbers, and so forth. It's the details that users are looking for when they retrieve a contact.
    You can give them all the details for a contact, or only display details of a particular type,
    such as email addresses.
</p>
<p>
    The steps in this lesson assume that you already have a
    {@link android.provider.ContactsContract.Contacts} row for a contact the user has picked.
    The <a href="retrieve-names.html">Retrieving Contact Names</a> lesson shows how to
    retrieve a list of contacts.
</p>
<h2 id="RetrieveAll">Retrieve All Details for a Contact</h2>
<p>
    To retrieve all the details for a contact, search the
    {@link android.provider.ContactsContract.Data} table for any rows that contain the contact's
    {@link android.provider.ContactsContract.Data#LOOKUP_KEY}. This column is available in
    the {@link android.provider.ContactsContract.Data} table, because the Contacts
    Provider makes an implicit join between the {@link android.provider.ContactsContract.Contacts}
    table and the {@link android.provider.ContactsContract.Data} table. The
    {@link android.provider.ContactsContract.Contacts#LOOKUP_KEY} column is described
    in more detail in the <a href="retrieve-names.html">Retrieving Contact Names</a> lesson.
</p>
<p class="note">
    <strong>Note:</strong> Retrieving all the details for a contact reduces the performance of a
    device, because it needs to retrieve all of the columns in the
    {@link android.provider.ContactsContract.Data} table. Consider the performance impact before
    you use this technique.
</p>
<h3>Request permissions</h3>
<p>
    To read from the Contacts Provider, your app must have
    {@link android.Manifest.permission#READ_CONTACTS READ_CONTACTS} permission.
    To request this permission, add the following child element of
    <code><a href="{@docRoot}guide/topics/manifest/manifest-element.html">
    &lt;manifest&gt;</a></code> to your manifest file:
</p>
<pre>
    &lt;uses-permission android:name="android.permission.READ_CONTACTS" /&gt;
</pre>
<h3>Set up a projection</h3>
<p>
    Depending on the data type a row contains, it may use only a few columns or many. In addition,
    the data is in different columns depending on the data type.
    To ensure you get all the possible columns for all possible data types, you need to add all the
    column names to your projection. Always retrieve
    {@link android.provider.ContactsContract.Data#_ID Data._ID} if you're binding the result
    {@link android.database.Cursor} to a {@link android.widget.ListView}; otherwise, the binding
    won't work. Also retrieve {@link android.provider.ContactsContract.Data#MIMETYPE Data.MIMETYPE}
    so you can identify the data type of each row you retrieve. For example:
</p>
<pre>
    private static final String PROJECTION =
            {
                Data._ID,
                Data.MIMETYPE,
                Data.DATA1,
                Data.DATA2,
                Data.DATA3,
                Data.DATA4,
                Data.DATA5,
                Data.DATA6,
                Data.DATA7,
                Data.DATA8,
                Data.DATA9,
                Data.DATA10,
                Data.DATA11,
                Data.DATA12,
                Data.DATA13,
                Data.DATA14,
                Data.DATA15
            };
</pre>
<p>
    This projection retrieves all the columns for a row in the
    {@link android.provider.ContactsContract.Data} table, using the column names defined in
    the {@link android.provider.ContactsContract.Data} class.
</p>
<p>
    Optionally, you can also use any other column constants defined in or inherited by the
    {@link android.provider.ContactsContract.Data} class. Notice, however, that the columns
    {@link android.provider.ContactsContract.DataColumns#SYNC1} through
    {@link android.provider.ContactsContract.DataColumns#SYNC4} are meant to be used by sync
    adapters, so their data is not useful.
</p>
<h3>Define the selection criteria</h3>
<p>
    Define a constant for your selection clause, an array to hold selection arguments, and a
    variable to hold the selection value. Use
    the {@link android.provider.ContactsContract.Contacts#LOOKUP_KEY Contacts.LOOKUP_KEY} column to
    find the contact. For example:
</p>
<pre>
    // Defines the selection clause
    private static final String SELECTION = Data.LOOKUP_KEY + " = ?";
    // Defines the array to hold the search criteria
    private String[] mSelectionArgs = { "" };
    /*
     * Defines a variable to contain the selection value. Once you
     * have the Cursor from the Contacts table, and you've selected
     * the desired row, move the row's LOOKUP_KEY value into this
     * variable.
     */
    private String mLookupKey;
</pre>
<p>
    Using "?" as a placeholder in your selection text expression ensures that the resulting search
    is generated by binding rather than SQL compilation. This approach eliminates the
    possibility of malicious SQL injection.
</p>
<h3>Define the sort order</h3>
<p>
    Define the sort order you want in the resulting {@link android.database.Cursor}. To
    keep all rows for a particular data type together, sort by
    {@link android.provider.ContactsContract.Data#MIMETYPE Data.MIMETYPE}. This query argument
    groups all email rows together, all phone rows together, and so forth. For example:
</p>
<pre>
    /*
     * Defines a string that specifies a sort order of MIME type
     */
    private static final String SORT_ORDER = Data.MIMETYPE;
</pre>
<p class="note">
    <strong>Note:</strong> Some data types don't use a subtype, so you can't sort on subtype.
    Instead, you have to iterate through the returned {@link android.database.Cursor},
    determine the data type of the current row, and store data for rows that use a subtype. When
    you finish reading the cursor, you can then sort each data type by subtype and display the
    results.
</p>
<h3>Initialize the Loader</h3>
<p>
   Always do retrievals from the Contacts Provider (and all other content providers) in a
   background thread. Use the Loader framework defined by the
   {@link android.support.v4.app.LoaderManager} class and the
   {@link android.support.v4.app.LoaderManager.LoaderCallbacks} interface to do background
   retrievals.
</p>
<p>
    When you're ready to retrieve the rows, initialize the loader framework by
    calling {@link android.support.v4.app.LoaderManager#initLoader initLoader()}. Pass an
    integer identifier to the method; this identifier is passed to
    {@link android.support.v4.app.LoaderManager.LoaderCallbacks} methods. The identifier helps you
    use multiple loaders in an app by allowing you to differentiate between them.
</p>
<p>
    The following snippet shows how to initialize the loader framework:
</p>
<pre>
public class DetailsFragment extends Fragment implements
        LoaderManager.LoaderCallbacks&lt;Cursor&gt; {
    ...
    // Defines a constant that identifies the loader
    DETAILS_QUERY_ID = 0;
    ...
    /*
     * Invoked when the parent Activity is instantiated
     * and the Fragment's UI is ready. Put final initialization
     * steps here.
     */
    &#64;Override
    onActivityCreated(Bundle savedInstanceState) {
        ...
        // Initializes the loader framework
        getLoaderManager().initLoader(DETAILS_QUERY_ID, null, this);
</pre>
<h3>Implement onCreateLoader()</h3>
<p>
    Implement the {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onCreateLoader
    onCreateLoader()} method, which is called by the loader framework immediately after you call
    {@link android.support.v4.app.LoaderManager#initLoader initLoader()}. Return a
    {@link android.support.v4.content.CursorLoader} from this method. Since you're searching
    the {@link android.provider.ContactsContract.Data} table, use the constant
    {@link android.provider.ContactsContract.Data#CONTENT_URI Data.CONTENT_URI} as the content URI.
    For example:
</p>
<pre>
    &#64;Override
    public Loader&lt;Cursor&gt; onCreateLoader(int loaderId, Bundle args) {
        // Choose the proper action
        switch (loaderId) {
            case DETAILS_QUERY_ID:
            // Assigns the selection parameter
            mSelectionArgs[0] = mLookupKey;
            // Starts the query
            CursorLoader mLoader =
                    new CursorLoader(
                            getActivity(),
                            Data.CONTENT_URI,
                            PROJECTION,
                            SELECTION,
                            mSelectionArgs,
                            SORT_ORDER
                    );
            ...
    }
</pre>
<h3>Implement onLoadFinished() and onLoaderReset()</h3>
<p>
    Implement the
    {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}
    method. The loader framework calls
    {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}
    when the Contacts Provider returns the results of the query. For example:
</p>
<pre>
    public void onLoadFinished(Loader&lt;Cursor&gt; loader, Cursor cursor) {
        switch (loader.getId()) {
            case DETAILS_QUERY_ID:
                    /*
                     * Process the resulting Cursor here.
                     */
                }
                break;
            ...
        }
    }
</pre>
<p>
<p>
    The method {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset
    onLoaderReset()} is invoked when the loader framework detects that the data backing the result
    {@link android.database.Cursor} has changed. At this point, remove any existing references
    to the {@link android.database.Cursor} by setting them to null. If you don't, the loader
    framework won't destroy the old {@link android.database.Cursor}, and you'll get a memory
    leak. For example:
<pre>
    &#64;Override
    public void onLoaderReset(Loader&lt;Cursor&gt; loader) {
        switch (loader.getId()) {
            case DETAILS_QUERY_ID:
                /*
                 * If you have current references to the Cursor,
                 * remove them here.
                 */
                }
                break;
    }
</pre>
<h2 id="RetrieveSpecific">Retrieve Specific Details for a Contact</h2>
<p>
    Retrieving a specific data type for a contact, such as all the emails, follows the same pattern
    as retrieving all details. These are the only changes you need to make to the code
    listed in <a href="#RetrieveAll">Retrieve All Details for a Contact</a>:
</p>
<dl>
    <dt>
        Projection
    </dt>
    <dd>
        Modify your projection to retrieve the columns that are specific to the
        data type. Also modify the projection to use the column name constants defined in the
        {@link android.provider.ContactsContract.CommonDataKinds} subclass corresponding to the
        data type.
    </dd>
    <dt>
        Selection
    </dt>
    <dd>
        Modify the selection text to search for the
        {@link android.provider.ContactsContract.Data#MIMETYPE MIMETYPE} value that's specific to
        your data type.
    </dd>
    <dt>
        Sort order
    </dt>
    <dd>
        Since you're only selecting a single detail type, don't group the returned
        {@link android.database.Cursor} by {@link android.provider.ContactsContract.Data#MIMETYPE
        Data.MIMETYPE}.
    </dd>
</dl>
<p>
    These modifications are described in the following sections.
</p>
<h3>Define a projection</h3>
<p>
    Define the columns you want to retrieve, using the column name constants in the subclass
    of {@link android.provider.ContactsContract.CommonDataKinds} for the data type.
    If you plan to bind your {@link android.database.Cursor} to a {@link android.widget.ListView},
    be sure to retrieve the <code>_ID</code> column. For example, to retrieve email data, define the
    following projection:
</p>
<pre>
    private static final String[] PROJECTION =
            {
                Email._ID,
                Email.ADDRESS,
                Email.TYPE,
                Email.LABEL
            };
</pre>
<p>
    Notice that this projection uses the column names defined in the class
    {@link android.provider.ContactsContract.CommonDataKinds.Email}, instead of the column names
    defined in the class {@link android.provider.ContactsContract.Data}. Using the email-specific
    column names makes the code more readable.
</p>
<p>
    In the projection, you can also use any of the other columns defined in the
    {@link android.provider.ContactsContract.CommonDataKinds} subclass.
</p>
<h3>Define selection criteria</h3>
<p>
    Define a search text expression that retrieves rows for a specific contact's
    {@link android.provider.ContactsContract.Data#LOOKUP_KEY} and the
    {@link android.provider.ContactsContract.Data#MIMETYPE Data.MIMETYPE} of the details you
    want. Enclose the {@link android.provider.ContactsContract.Data#MIMETYPE MIMETYPE} value in
    single quotes by concatenating a "<code>'</code>" (single-quote) character to the start and end
    of the constant; otherwise, the provider interprets the constant as a variable name rather
    than as a string value. You don't need to use a placeholder for this value, because you're
    using a constant rather than a user-supplied value. For example:
</p>
<pre>
    /*
     * Defines the selection clause. Search for a lookup key
     * and the Email MIME type
     */
    private static final String SELECTION =
            Data.LOOKUP_KEY + " = ?" +
            " AND " +
            Data.MIMETYPE + " = " +
            "'" + Email.CONTENT_ITEM_TYPE + "'";
    // Defines the array to hold the search criteria
    private String[] mSelectionArgs = { "" };
</pre>
<h3>Define a sort order</h3>
<p>
    Define a sort order for the returned {@link android.database.Cursor}. Since you're retrieving a
    specific data type, omit the sort on {@link android.provider.ContactsContract.Data#MIMETYPE}.
    Instead, if the type of detail data you're searching includes a subtype, sort on it.
    For example, for email data you can sort on
    {@link android.provider.ContactsContract.CommonDataKinds.Email#TYPE Email.TYPE}:
</p>
<pre>
    private static final String SORT_ORDER = Email.TYPE + " ASC ";
</pre>