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Retrieving a List of Contacts

This lesson shows you how to retrieve a list of contacts whose data matches all or part of a search string, using the following techniques:

Match contact names
Retrieve a list of contacts by matching the search string to all or part of the contact name data. The Contacts Provider allows multiple instances of the same name, so this technique can return a list of matches.
Match a specific type of data, such as a phone number
Retrieve a list of contacts by matching the search string to a particular type of detail data such as an email address. For example, this technique allows you to list all of the contacts whose email address matches the search string.
Match any type of data
Retrieve a list of contacts by matching the search string to any type of detail data, including name, phone number, street address, email address, and so forth. For example, this technique allows you to accept any type of data for a search string and then list the contacts for which the data matches the string.

Note: All the examples in this lesson use a CursorLoader to retrieve data from the Contacts Provider. A CursorLoader runs its query on a thread that's separate from the UI thread. This ensures that the query doesn't slow down UI response times and cause a poor user experience. For more information, see the Android training class Loading Data in the Background.

Request Permission to Read the Provider

To do any type of search of the Contacts Provider, your app must have READ_CONTACTS permission. To request this, add this <uses-permission> element to your manifest file as a child element of <manifest>:

    <uses-permission android:name="android.permission.READ_CONTACTS" />

Match a Contact by Name and List the Results

This technique tries to match a search string to the name of a contact or contacts in the Contact Provider's ContactsContract.Contacts table. You usually want to display the results in a ListView, to allow the user to choose among the matched contacts.

Define ListView and item layouts

To display the search results in a ListView, you need a main layout file that defines the entire UI including the ListView, and an item layout file that defines one line of the ListView. For example, you could create the main layout file res/layout/contacts_list_view.xml with the following XML:

<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@android:id/list"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/>

This XML uses the built-in Android ListView widget android:id/list.

Define the item layout file contacts_list_item.xml with the following XML:

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@android:id/text1"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:clickable="true"/>

This XML uses the built-in Android TextView widget android:text1.

Note: This lesson doesn't describe the UI for getting a search string from the user, because you may want to get the string indirectly. For example, you can give the user an option to search for contacts whose name matches a string in an incoming text message.

The two layout files you've written define a user interface that shows a ListView. The next step is to write code that uses this UI to display a list of contacts.

Define a Fragment that displays the list of contacts

To display the list of contacts, start by defining a Fragment that's loaded by an Activity. Using a Fragment is a more flexible technique, because you can use one Fragment to display the list and a second Fragment to display the details for a contact that the user chooses from the list. Using this approach, you can combine one of the techniques presented in this lesson with one from the lesson Retrieving Details for a Contact.

To learn how to use one or more Fragment objects from an an Activity, read the training class Building a Dynamic UI with Fragments.

To help you write queries against the Contacts Provider, the Android framework provides a contracts class called ContactsContract, which defines useful constants and methods for accessing the provider. When you use this class, you don't have to define your own constants for content URIs, table names, or columns. To use this class, include the following statement:

import android.provider.ContactsContract;

Since the code uses a CursorLoader to retrieve data from the provider, you must specify that it implements the loader interface LoaderManager.LoaderCallbacks. Also, to help detect which contact the user selects from the list of search results, implement the adapter interface AdapterView.OnItemClickListener. For example:

...
import android.support.v4.app.Fragment;
import android.support.v4.app.LoaderManager.LoaderCallbacks;
import android.widget.AdapterView;
...
public class ContactsFragment extends Fragment implements
        LoaderManager.LoaderCallbacks<Cursor>,
        AdapterView.OnItemClickListener {

Define global variables

Define global variables that are used in other parts of the code:

    ...
    /*
     * Defines an array that contains column names to move from
     * the Cursor to the ListView.
     */
    @SuppressLint("InlinedApi")
    private final static String[] FROM_COLUMNS = {
            Build.VERSION.SDK_INT
                    >= Build.VERSION_CODES.HONEYCOMB ?
                    Contacts.DISPLAY_NAME_PRIMARY :
                    Contacts.DISPLAY_NAME
    };
    /*
     * Defines an array that contains resource ids for the layout views
     * that get the Cursor column contents. The id is pre-defined in
     * the Android framework, so it is prefaced with "android.R.id"
     */
    private final static int[] TO_IDS = {
           android.R.id.text1
    };
    // Define global mutable variables
    // Define a ListView object
    ListView mContactsList;
    // Define variables for the contact the user selects
    // The contact's _ID value
    long mContactId;
    // The contact's LOOKUP_KEY
    String mContactKey;
    // A content URI for the selected contact
    Uri mContactUri;
    // An adapter that binds the result Cursor to the ListView
    private SimpleCursorAdapter mCursorAdapter;
    ...

Note: Since Contacts.DISPLAY_NAME_PRIMARY requires Android 3.0 (API version 11) or later, setting your app's minSdkVersion to 10 or below generates an Android Lint warning in Android Studio. To turn off this warning, add the annotation @SuppressLint("InlinedApi") before the definition of FROM_COLUMNS.

Initialize the Fragment

Initialize the Fragment. Add the empty, public constructor required by the Android system, and inflate the Fragment object's UI in the callback method onCreateView(). For example:

    // Empty public constructor, required by the system
    public ContactsFragment() {}

    // A UI Fragment must inflate its View
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the fragment layout
        return inflater.inflate(R.layout.contact_list_fragment,
            container, false);
    }

Set up the CursorAdapter for the ListView

Set up the SimpleCursorAdapter that binds the results of the search to the ListView. To get the ListView object that displays the contacts, you need to call Activity.findViewById() using the parent activity of the Fragment. Use the Context of the parent activity when you call setAdapter(). For example:

    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ...
        // Gets the ListView from the View list of the parent activity
        mContactsList =
            (ListView) getActivity().findViewById(R.layout.contact_list_view);
        // Gets a CursorAdapter
        mCursorAdapter = new SimpleCursorAdapter(
                getActivity(),
                R.layout.contact_list_item,
                null,
                FROM_COLUMNS, TO_IDS,
                0);
        // Sets the adapter for the ListView
        mContactsList.setAdapter(mCursorAdapter);
    }

Set the selected contact listener

When you display the results of a search, you usually want to allow the user to select a single contact for further processing. For example, when the user clicks a contact you can display the contact's address on a map. To provide this feature, you first defined the current Fragment as the click listener by specifying that the class implements AdapterView.OnItemClickListener, as shown in the section Define a Fragment that displays the list of contacts.

To continue setting up the listener, bind it to the ListView by calling the method setOnItemClickListener() in onActivityCreated(). For example:

    public void onActivityCreated(Bundle savedInstanceState) {
        ...
        // Set the item click listener to be the current fragment.
        mContactsList.setOnItemClickListener(this);
        ...
    }

Since you specified that the current Fragment is the OnItemClickListener for the ListView, you now need to implement its required method onItemClick(), which handles the click event. This is described in a succeeding section.

Define a projection

Define a constant that contains the columns you want to return from your query. Each item in the ListView displays the contact's display name, which contains the main form of the contact's name. In Android 3.0 (API version 11) and later, the name of this column is Contacts.DISPLAY_NAME_PRIMARY; in versions previous to that, its name is Contacts.DISPLAY_NAME.

The column Contacts._ID is used by the SimpleCursorAdapter binding process. Contacts._ID and LOOKUP_KEY are used together to construct a content URI for the contact the user selects.

...
@SuppressLint("InlinedApi")
private static final String[] PROJECTION =
        {
            Contacts._ID,
            Contacts.LOOKUP_KEY,
            Build.VERSION.SDK_INT
                    >= Build.VERSION_CODES.HONEYCOMB ?
                    Contacts.DISPLAY_NAME_PRIMARY :
                    Contacts.DISPLAY_NAME

        };

Define constants for the Cursor column indexes

To get data from an individual column in a Cursor, you need the column's index within the Cursor. You can define constants for the indexes of the Cursor columns, because the indexes are the same as the order of the column names in your projection. For example:

// The column index for the _ID column
private static final int CONTACT_ID_INDEX = 0;
// The column index for the LOOKUP_KEY column
private static final int LOOKUP_KEY_INDEX = 1;

Specify the selection criteria

To specify the data you want, create a combination of text expressions and variables that tell the provider the data columns to search and the values to find.

For the text expression, define a constant that lists the search columns. Although this expression can contain values as well, the preferred practice is to represent the values with a "?" placeholder. During retrieval, the placeholder is replaced with values from an array. Using "?" as a placeholder ensures that the search specification is generated by binding rather than by SQL compilation. This practice eliminates the possibility of malicious SQL injection. For example:

    // Defines the text expression
    @SuppressLint("InlinedApi")
    private static final String SELECTION =
            Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
            Contacts.DISPLAY_NAME_PRIMARY + " LIKE ?" :
            Contacts.DISPLAY_NAME + " LIKE ?";
    // Defines a variable for the search string
    private String mSearchString;
    // Defines the array to hold values that replace the ?
    private String[] mSelectionArgs = { mSearchString };

Define the onItemClick() method

In a previous section, you set the item click listener for the ListView. Now implement the action for the listener by defining the method AdapterView.OnItemClickListener.onItemClick():

    @Override
    public void onItemClick(
        AdapterView<?> parent, View item, int position, long rowID) {
        // Get the Cursor
        Cursor cursor = parent.getAdapter().getCursor();
        // Move to the selected contact
        cursor.moveToPosition(position);
        // Get the _ID value
        mContactId = getLong(CONTACT_ID_INDEX);
        // Get the selected LOOKUP KEY
        mContactKey = getString(CONTACT_KEY_INDEX);
        // Create the contact's content Uri
        mContactUri = Contacts.getLookupUri(mContactId, mContactKey);
        /*
         * You can use mContactUri as the content URI for retrieving
         * the details for a contact.
         */
    }

Initialize the loader

Since you're using a CursorLoader to retrieve data, you must initialize the background thread and other variables that control asynchronous retrieval. Do the initialization in onActivityCreated(), which is invoked immediately before the Fragment UI appears, as shown in the following example:

public class ContactsFragment extends Fragment implements
        LoaderManager.LoaderCallbacks<Cursor> {
    ...
    // Called just before the Fragment displays its UI
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        // Always call the super method first
        super.onActivityCreated(savedInstanceState);
        ...
        // Initializes the loader
        getLoaderManager().initLoader(0, null, this);

Implement onCreateLoader()

Implement the method onCreateLoader(), which is called by the loader framework immediately after you call initLoader().

In onCreateLoader(), set up the search string pattern. To make a string into a pattern, insert "%" (percent) characters to represent a sequence of zero or more characters, or "_" (underscore) characters to represent a single character, or both. For example, the pattern "%Jefferson%" would match both "Thomas Jefferson" and "Jefferson Davis".

Return a new CursorLoader from the method. For the content URI, use Contacts.CONTENT_URI. This URI refers to the entire table, as shown in the following example:

    ...
    @Override
    public Loader<Cursor> onCreateLoader(int loaderId, Bundle args) {
        /*
         * Makes search string into pattern and
         * stores it in the selection array
         */
        mSelectionArgs[0] = "%" + mSearchString + "%";
        // Starts the query
        return new CursorLoader(
                getActivity(),
                Contacts.CONTENT_URI,
                PROJECTION,
                SELECTION,
                mSelectionArgs,
                null
        );
    }

Implement onLoadFinished() and onLoaderReset()

Implement the onLoadFinished() method. The loader framework calls onLoadFinished() when the Contacts Provider returns the results of the query. In this method, put the result Cursor in the SimpleCursorAdapter. This automatically updates the ListView with the search results:

    public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
        // Put the result Cursor in the adapter for the ListView
        mCursorAdapter.swapCursor(cursor);
    }

The method onLoaderReset() is invoked when the loader framework detects that the result Cursor contains stale data. Delete the SimpleCursorAdapter reference to the existing Cursor. If you don't, the loader framework will not recycle the Cursor, which causes a memory leak. For example:

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        // Delete the reference to the existing Cursor
        mCursorAdapter.swapCursor(null);

    }

You now have the key pieces of an app that matches a search string to contact names and returns the result in a ListView. The user can click a contact name to select it. This triggers a listener, in which you can work further with the contact's data. For example, you can retrieve the contact's details. To learn how to do this, continue with the next lesson, Retrieving Details for a Contact.

To learn more about search user interfaces, read the API guide Creating a Search Interface.

The remaining sections in this lesson demonstrate other ways of finding contacts in the Contacts Provider.

Match a Contact By a Specific Type of Data

This technique allows you to specify the type of data you want to match. Retrieving by name is a specific example of this type of query, but you can also do it for any of the types of detail data associated with a contact. For example, you can retrieve contacts that have a specific postal code; in this case, the search string has to match data stored in a postal code row.

To implement this type of retrieval, first implement the following code, as listed in previous sections:

The following steps show you the additional code you need to match a search string to a particular type of detail data and display the results.

Choose the data type and table

To search for a particular type of detail data, you have to know the custom MIME type value for the data type. Each data type has a unique MIME type value defined by a constant CONTENT_ITEM_TYPE in the subclass of ContactsContract.CommonDataKinds associated with the data type. The subclasses have names that indicate their data type; for example, the subclass for email data is ContactsContract.CommonDataKinds.Email, and the custom MIME type for email data is defined by the constant Email.CONTENT_ITEM_TYPE.

Use the ContactsContract.Data table for your search. All of the constants you need for your projection, selection clause, and sort order are defined in or inherited by this table.

Define a projection

To define a projection, choose one or more of the columns defined in ContactsContract.Data or the classes from which it inherits. The Contacts Provider does an implicit join between ContactsContract.Data and other tables before it returns rows. For example:

    @SuppressLint("InlinedApi")
    private static final String[] PROJECTION =
        {
            /*
             * The detail data row ID. To make a ListView work,
             * this column is required.
             */
            Data._ID,
            // The primary display name
            Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
                    Data.DISPLAY_NAME_PRIMARY :
                    Data.DISPLAY_NAME,
            // The contact's _ID, to construct a content URI
            Data.CONTACT_ID
            // The contact's LOOKUP_KEY, to construct a content URI
            Data.LOOKUP_KEY (a permanent link to the contact
        };

Define search criteria

To search for a string within a particular type of data, construct a selection clause from the following:

For example:

    /*
     * Constructs search criteria from the search string
     * and email MIME type
     */
    private static final String SELECTION =
            /*
             * Searches for an email address
             * that matches the search string
             */
            Email.ADDRESS + " LIKE ? " + "AND " +
            /*
             * Searches for a MIME type that matches
             * the value of the constant
             * Email.CONTENT_ITEM_TYPE. Note the
             * single quotes surrounding Email.CONTENT_ITEM_TYPE.
             */
            Data.MIMETYPE + " = '" + Email.CONTENT_ITEM_TYPE + "'";

Next, define variables to contain the selection argument:

    String mSearchString;
    String[] mSelectionArgs = { "" };

Implement onCreateLoader()

Now that you've specified the data you want and how to find it, define a query in your implementation of onCreateLoader(). Return a new CursorLoader from this method, using your projection, selection text expression, and selection array as arguments. For a content URI, use Data.CONTENT_URI. For example:

    @Override
    public Loader<Cursor> onCreateLoader(int loaderId, Bundle args) {
        // OPTIONAL: Makes search string into pattern
        mSearchString = "%" + mSearchString + "%";
        // Puts the search string into the selection criteria
        mSelectionArgs[0] = mSearchString;
        // Starts the query
        return new CursorLoader(
                getActivity(),
                Data.CONTENT_URI,
                PROJECTION,
                SELECTION,
                mSelectionArgs,
                null
        );
    }

These code snippets are the basis of a simple reverse lookup based on a specific type of detail data. This is the best technique to use if your app focuses on a particular type of data, such as emails, and you want allow users to get the names associated with a piece of data.

Match a Contact By Any Type of Data

Retrieving a contact based on any type of data returns contacts if any of their data matches a the search string, including name, email address, postal address, phone number, and so forth. This results in a broad set of search results. For example, if the search string is "Doe", then searching for any data type returns the contact "John Doe"; it also returns contacts who live on "Doe Street".

To implement this type of retrieval, first implement the following code, as listed in previous sections:

The following steps show you the additional code you need to match a search string to any type of data and display the results.

Remove selection criteria

Don't define the SELECTION constants or the mSelectionArgs variable. These aren't used in this type of retrieval.

Implement onCreateLoader()

Implement the onCreateLoader() method, returning a new CursorLoader. You don't need to convert the search string into a pattern, because the Contacts Provider does that automatically. Use Contacts.CONTENT_FILTER_URI as the base URI, and append your search string to it by calling Uri.withAppendedPath(). Using this URI automatically triggers searching for any data type, as shown in the following example:

    @Override
    public Loader<Cursor> onCreateLoader(int loaderId, Bundle args) {
        /*
         * Appends the search string to the base URI. Always
         * encode search strings to ensure they're in proper
         * format.
         */
        Uri contentUri = Uri.withAppendedPath(
                Contacts.CONTENT_FILTER_URI,
                Uri.encode(mSearchString));
        // Starts the query
        return new CursorLoader(
                getActivity(),
                contentUri,
                PROJECTION,
                null,
                null,
                null
        );
    }

These code snippets are the basis of an app that does a broad search of the Contacts Provider. The technique is useful for apps that want to implement functionality similar to the People app's contact list screen.

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