docs/html/guide/topics/providers/content-provider-basics.jd

page.title=Content Provider Basics
@jd:body
<div id="qv-wrapper">
<div id="qv">
<!-- In this document -->
<h2>In this document</h2>
<ol>
    <li>
        <a href="#Basics">Overview</a>
        <ol>
            <li>
                <a href="#ClientProvider">Accessing a provider</a>
            </li>
            <li>
                <a href="#ContentURIs">Content URIs</a>
            </li>
        </ol>
    </li>
    <li>
        <a href="#SimpleQuery">Retrieving Data from the Provider</a>
        <ol>
            <li>
                <a href="#RequestPermissions">Requesting read access permission</a>
            </li>
            <li>
                <a href="#Query">Constructing the query</a>
            </li>
            <li>
                <a href="#DisplayResults">Displaying query results</a>
            </li>
            <li>
                <a href="#GettingResults">Getting data from query results</a>
            </li>
        </ol>
    </li>
    <li>
        <a href="#Permissions">Content Provider Permissions</a>
    </li>
    <li>
        <a href="#Modifications">Inserting, Updating, and Deleting Data</a>
        <ol>
            <li>
                <a href="#Inserting">Inserting data</a>
            </li>
            <li>
                <a href="#Updating">Updating data</a>
            </li>
            <li>
                <a href="#Deleting">Deleting data</a>
            </li>
        </ol>
    </li>
    <li>
        <a href="#DataTypes">Provider Data Types</a>
    </li>
    <li>
        <a href="#AltForms">Alternative Forms of Provider Access</a>
        <ol>
            <li>
                <a href="#Batch">Batch access</a>
            </li>
            <li>
                <a href="#Intents">Data access via intents</a>
            </li>
        </ol>
    </li>
    <li>
        <a href="#ContractClasses">Contract Classes</a>
    </li>
    <li>
        <a href="#MIMETypeReference">MIME Type Reference</a>
    </li>
</ol>

    <!-- Key Classes -->
<h2>Key classes</h2>
    <ol>
        <li>
            {@link android.content.ContentProvider}
        </li>
        <li>
            {@link android.content.ContentResolver}
        </li>
        <li>
            {@link android.database.Cursor}
        </li>
        <li>
            {@link android.net.Uri}
        </li>
    </ol>

    <!-- Related Samples -->
<h2>Related Samples</h2>
    <ol>
        <li>
        <a
        href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/view/List2.html">
        Cursor (People)</a>
        </li>
        <li>
        <a
        href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/view/List7.html">
        Cursor (Phones)</a>
        </li>
    </ol>

    <!-- See also -->
<h2>See also</h2>
    <ol>
        <li>
            <a href="{@docRoot}guide/topics/providers/content-provider-creating.html">
            Creating a Content Provider</a>
        </li>
        <li>
            <a href="{@docRoot}guide/topics/providers/calendar-provider.html">
            Calendar Provider</a>
        </li>
    </ol>
</div>
</div>

    <!-- Intro paragraphs -->
<p>
    A content provider manages access to a central repository of data. A provider
    is part of an Android application, which often provides its own UI for working with
    the data. However, content providers are primarily intended to be used by other
    applications, which access the provider using a provider client object. Together, providers
    and provider clients offer a consistent, standard interface to data that also handles
    inter-process communication and secure data access.
</p>
<p>
    This topic describes the basics of the following:
</p>
    <ul>
        <li>How content providers work.</li>
        <li>The API you use retrieve data from a content provider.</li>
        <li>The API you use to insert, update, or delete data in a content provider.</li>
        <li>Other API features that facilitate working with providers.</li>
    </ul>

    <!-- Basics -->
<h2 id="Basics">Overview</h2>
<p>
    A content provider presents data to external applications as one or more tables that are
    similar to the tables found in a relational database. A row represents an instance of some type
    of data the provider collects, and each column in the row represents an individual piece of
    data collected for an instance.
</p>
<p>
    For example, one of the built-in providers in the Android platform is the user dictionary, which
    stores the spellings of non-standard words that the user wants to keep. Table 1 illustrates what
    the data might look like in this provider's table:
</p>
<p class="table-caption">
    <strong>Table 1:</strong> Sample user dictionary table.
</p>
<table id="table1" style="width: 50%;">
    <tr>
        <th style="width:20%" align="center" scope="col">word</th>
        <th style="width:20%" align="center" scope="col">app id</th>
        <th style="width:20%" align="center" scope="col">frequency</th>
        <th style="width:20%" align="center" scope="col">locale</th>
        <th style="width:20%" align="center" scope="col">_ID</th>
    </tr>
    <tr>
        <td align="center" scope="row">mapreduce</td>
        <td align="center">user1</td>
        <td align="center">100</td>
        <td align="center">en_US</td>
        <td align="center">1</td>
    </tr>
    <tr>
        <td align="center" scope="row">precompiler</td>
        <td align="center">user14</td>
        <td align="center">200</td>
        <td align="center">fr_FR</td>
        <td align="center">2</td>
    </tr>
    <tr>
        <td align="center" scope="row">applet</td>
        <td align="center">user2</td>
        <td align="center">225</td>
        <td align="center">fr_CA</td>
        <td align="center">3</td>
    </tr>
    <tr>
        <td align="center" scope="row">const</td>
        <td align="center">user1</td>
        <td align="center">255</td>
        <td align="center">pt_BR</td>
        <td align="center">4</td>
    </tr>
    <tr>
        <td align="center" scope="row">int</td>
        <td align="center">user5</td>
        <td align="center">100</td>
        <td align="center">en_UK</td>
        <td align="center">5</td>
    </tr>
</table>
<p>
    In table 1, each row represents an instance of a word that might not be
    found in a standard dictionary. Each column represents some data for that word, such as the
    locale in which it was first encountered. The column headers are column names that are stored in
    the provider. To refer to a row's locale, you refer to its <code>locale</code> column. For
    this provider, the <code>_ID</code> column serves as a "primary key" column that
    the provider automatically maintains.
</p>
<p class="note">
    <strong>Note:</strong> A provider isn't required to have a primary key, and it isn't required
    to use <code>_ID</code> as the column name of a primary key if one is present. However,
    if you want to bind data from a provider to a {@link android.widget.ListView}, one of the
    column names has to be <code>_ID</code>. This requirement is explained in more detail in the
    section <a href="#DisplayResults">Displaying query results</a>.
</p>
<h3 id="ClientProvider">Accessing a provider</h3>
<p>
    An application accesses the data from a content provider with
    a {@link android.content.ContentResolver} client object. This object has methods that call
    identically-named methods in the provider object, an instance of one of the concrete
    subclasses of {@link android.content.ContentProvider}. The
    {@link android.content.ContentResolver} methods provide the basic
    "CRUD" (create, retrieve, update, and delete) functions of persistent storage.
</p>
<p>
    The {@link android.content.ContentResolver} object in the client application's
    process and the {@link android.content.ContentProvider} object in the application that owns
    the provider automatically handle inter-process communication.
    {@link android.content.ContentProvider} also acts as an abstraction layer between its
    repository of data and the external appearance of data as tables.
</p>
<p class="note">
    <strong>Note:</strong> To access a provider, your application usually has to request specific
    permissions in its manifest file. This is described in more detail in the section
    <a href="#Permissions">Content Provider Permissions</a>
</p>
<p>
    For example, to get a list of the words and their locales from the User Dictionary Provider,
    you call {@link android.content.ContentResolver#query ContentResolver.query()}.
    The {@link android.content.ContentResolver#query query()} method calls the
    {@link android.content.ContentProvider#query ContentProvider.query()} method defined by the 
    User Dictionary Provider. The following lines of code show a
    {@link android.content.ContentResolver#query ContentResolver.query()} call:
<p>
<pre>
// Queries the user dictionary and returns results
mCursor = getContentResolver().query(
    UserDictionary.Words.CONTENT_URI,   // The content URI of the words table
    mProjection,                        // The columns to return for each row
    mSelectionClause                    // Selection criteria
    mSelectionArgs,                     // Selection criteria
    mSortOrder);                        // The sort order for the returned rows
</pre>
<p>
    Table 2 shows how the arguments to
    {@link android.content.ContentResolver#query 
    query(Uri,projection,selection,selectionArgs,sortOrder)} match an SQL SELECT statement:
</p>
<p class="table-caption">
    <strong>Table 2:</strong> Query() compared to SQL query.
</p>
<table id="table2" style="width: 75%;">
    <tr>
        <th style="width:25%" align="center" scope="col">query() argument</th>
        <th style="width:25%" align="center" scope="col">SELECT keyword/parameter</th>
        <th style="width:50%" align="center" scope="col">Notes</th>
    </tr>
    <tr>
        <td align="center"><code>Uri</code></td>
        <td align="center"><code>FROM <em>table_name</em></code></td>
        <td><code>Uri</code> maps to the table in the provider named <em>table_name</em>.</td>
    </tr>
    <tr>
        <td align="center"><code>projection</code></td>
        <td align="center"><code><em>col,col,col,...</em></code></td>
        <td>
            <code>projection</code> is an array of columns that should be included for each row
            retrieved.
        </td>
    </tr>
    <tr>
        <td align="center"><code>selection</code></td>
        <td align="center"><code>WHERE <em>col</em> = <em>value</em></code></td>
        <td><code>selection</code> specifies the criteria for selecting rows.</td>
    </tr>
    <tr>
        <td align="center"><code>selectionArgs</code></td>
        <td align="center">
            (No exact equivalent. Selection arguments replace <code>?</code> placeholders in the
            selection clause.)
        </td>
    </tr>
    <tr>
        <td align="center"><code>sortOrder</code></td>
        <td align="center"><code>ORDER BY <em>col,col,...</em></code></td>
        <td>
            <code>sortOrder</code> specifies the order in which rows appear in the returned
            {@link android.database.Cursor}.
        </td>
    </tr>
</table>
<h3 id="ContentURIs">Content URIs</h3>
<p>
    A <strong>content URI</strong> is a URI that identifies data in a provider. Content URIs
    include the symbolic name of the entire provider (its <strong>authority</strong>) and a
    name that points to a table (a <strong>path</strong>). When you call
    a client method to access a table in a provider, the content URI for the table is one of
    the arguments.
</p>
<p>
    In the preceding lines of code, the constant
    {@link android.provider.UserDictionary.Words#CONTENT_URI} contains the content URI of
    the user dictionary's "words" table. The {@link android.content.ContentResolver}
    object parses out the URI's authority, and uses it to "resolve" the provider by
    comparing the authority to a system table of known providers. The
    {@link android.content.ContentResolver} can then dispatch the query arguments to the correct
    provider.
</p>
<p>
    The {@link android.content.ContentProvider} uses the path part of the content URI to choose the
    table to access. A provider usually has a <strong>path</strong> for each table it exposes.
</p>
<p>
    In the previous lines of code, the full URI for the "words" table is:
</p>
<pre>
content://user_dictionary/words
</pre>
<p>
    where the <code>user_dictionary</code> string is the provider's authority, and
    <code>words</code> string is the table's path. The string
    <code>content://</code> (the <strong>scheme</strong>) is always present,
    and identifies this as a content URI.
</p>
<p>
    Many providers allow you to access a single row in a table by appending an ID value
    to the end of the URI. For example, to retrieve a row whose <code>_ID</code> is
    <code>4</code> from user dictionary, you can use this content URI:
</p>
<pre>
Uri singleUri = ContentUris.withAppendedId(UserDictionary.Words.CONTENT_URI,4);
</pre>
<p>
    You often use id values when you've retrieved a set of rows and then want to update or delete
    one of them.
</p>
<p class="note">
    <strong>Note:</strong> The {@link android.net.Uri} and {@link android.net.Uri.Builder} classes
    contain convenience methods for constructing well-formed Uri objects from strings. The
    {@link android.content.ContentUris} contains convenience methods for appending id values to
    a URI. The previous snippet uses {@link android.content.ContentUris#withAppendedId
    withAppendedId()} to append an id to the UserDictionary content URI.
</p>


    <!-- Retrieving Data from the Provider -->
<h2 id="SimpleQuery">Retrieving Data from the Provider</h2>
<p>
    This section describes how to retrieve data from a provider, using the User Dictionary Provider
    as an example.
</p>
<p class="note">
    For the sake of clarity, the code snippets in this section call
    {@link android.content.ContentResolver#query ContentResolver.query()} on the "UI thread"". In 
    actual code, however, you should do queries asynchronously on a separate thread. One way to do 
    this is to use the {@link android.content.CursorLoader} class, which is described
    in more detail in the <a href="{@docRoot}guide/components/loaders.html">
    Loaders</a> guide. Also, the lines of code are snippets only; they don't show a complete
    application.
</p>
<p>
    To retrieve data from a provider, follow these basic steps:
</p>
<ol>
   <li>
        Request the read access permission for the provider.
   </li>
   <li>
        Define the code that sends a query to the provider.
   </li>
</ol>
<h3 id="RequestPermissions">Requesting read access permission</h3>
<p>
    To retrieve data from a provider, your application needs "read access permission" for the
    provider. You can't request this permission at run-time; instead, you have to specify that
    you need this permission in your manifest, using the
<code><a href="{@docRoot}guide/topics/manifest/uses-permission-element.html">&lt;uses-permission&gt;</a></code>
    element and the exact permission name defined by the
    provider. When you specify this element in your manifest, you are in effect "requesting" this
    permission for your application. When users install your application, they implicitly grant
    this request.
</p>
<p>
    To find the exact name of the read access permission for the provider you're using, as well
    as the names for other access permissions used by the provider, look in the provider's
    documentation.
</p>
<p>
    The role of permissions in accessing providers is described in more detail in the section
    <a href="#Permissions">Content Provider Permissions</a>.
</p>
<p>
    The User Dictionary Provider defines the permission
    <code>android.permission.READ_USER_DICTIONARY</code> in its manifest file, so an
    application that wants to read from the provider must request this permission.
</p>
<!-- Constructing the query -->
<h3 id="Query">Constructing the query</h3>
<p>
    The next step in retrieving data a provider is to construct a query. This first snippet
    defines some variables for accessing the User Dictionary Provider:
</p>
<pre class="prettyprint">

// A "projection" defines the columns that will be returned for each row
String[] mProjection =
{
    UserDictionary.Words._ID,    // Contract class constant for the _ID column name
    UserDictionary.Words.WORD,   // Contract class constant for the word column name
    UserDictionary.Words.LOCALE  // Contract class constant for the locale column name
};

// Defines a string to contain the selection clause
String mSelectionClause = null;

// Initializes an array to contain selection arguments
String[] mSelectionArgs = {""};

</pre>
<p>
    The next snippet shows how to use
    {@link android.content.ContentResolver#query ContentResolver.query()}, using the User Dictionary
    Provider as an example. A provider client query is similar to an SQL query, and it contains a 
    set of columns to return, a set of selection criteria, and a sort order.
</p>
<p>
    The set of columns that the query should return is called a <strong>projection</strong>
    (the variable <code>mProjection</code>).
</p>
<p>
    The expression that specifies the rows to retrieve is split into a selection clause and
    selection arguments. The selection clause is a combination of logical and Boolean expressions,
    column names, and values (the variable <code>mSelectionClause</code>). If you specify the 
    replaceable parameter <code>?</code> instead of a value, the query method retrieves the value 
    from the selection arguments array (the variable <code>mSelectionArgs</code>).
</p>
<p>
    In the next snippet, if the user doesn't enter a word, the selection clause is set to
    <code>null</code>, and the query returns all the words in the provider. If the user enters
    a word, the selection clause is set to <code>UserDictionary.Words.WORD + " = ?"</code> and
    the first element of selection arguments array is set to the word the user enters.
</p>
<pre class="prettyprint">
/*
 * This defines a one-element String array to contain the selection argument.
 */
String[] mSelectionArgs = {""};

// Gets a word from the UI
mSearchString = mSearchWord.getText().toString();

// Remember to insert code here to check for invalid or malicious input.

// If the word is the empty string, gets everything
if (TextUtils.isEmpty(mSearchString)) {
    // Setting the selection clause to null will return all words
    mSelectionClause = null;
    mSelectionArgs[0] = "";

} else {
    // Constructs a selection clause that matches the word that the user entered.
    mSelectionClause = UserDictionary.Words.WORD + " = ?";

    // Moves the user's input string to the selection arguments.
    mSelectionArgs[0] = mSearchString;

}

// Does a query against the table and returns a Cursor object
mCursor = getContentResolver().query(
    UserDictionary.Words.CONTENT_URI,  // The content URI of the words table
    mProjection,                       // The columns to return for each row
    mSelectionClause                   // Either null, or the word the user entered
    mSelectionArgs,                    // Either empty, or the string the user entered
    mSortOrder);                       // The sort order for the returned rows

// Some providers return null if an error occurs, others throw an exception
if (null == mCursor) {
    /*
     * Insert code here to handle the error. Be sure not to use the cursor! You may want to
     * call android.util.Log.e() to log this error.
     *
     */
// If the Cursor is empty, the provider found no matches
} else if (mCursor.getCount() &lt; 1) {

    /*
     * Insert code here to notify the user that the search was unsuccessful. This isn't necessarily
     * an error. You may want to offer the user the option to insert a new row, or re-type the
     * search term.
     */

} else {
    // Insert code here to do something with the results

}
</pre>
<p>
    This query is analogous to the SQL statement:
</p>
<pre>
SELECT _ID, word, locale FROM words WHERE word = &lt;userinput&gt; ORDER BY word ASC;
</pre>
<p>
    In this SQL statement, the actual column names are used instead of contract class constants.
</p>
<h4 id="Injection">Protecting against malicious input</h4>
<p>
    If the data managed by the content provider is in an SQL database, including external untrusted
    data into raw SQL statements can lead to SQL injection.
</p>
<p>
    Consider this selection clause:
</p>
<pre>
// Constructs a selection clause by concatenating the user's input to the column name
String mSelectionClause =  "var = " + mUserInput;
</pre>
<p>
    If you do this, you're allowing the user to concatenate malicious SQL onto your SQL statement.
    For example, the user could enter "nothing; DROP TABLE *;"  for <code>mUserInput</code>, which
    would result in the selection clause <code>var = nothing; DROP TABLE *;</code>. Since the
    selection clause is treated as an SQL statement, this might cause the provider to erase all of
    the tables in the underlying SQLite database (unless the provider is set up to catch
    <a href="http://en.wikipedia.org/wiki/SQL_injection">SQL injection</a> attempts).
</p>
<p>
    To avoid this problem, use a selection clause that uses <code>?</code> as a replaceable
    parameter and a separate array of selection arguments. When you do this, the user input
    is bound directly to the query rather than being interpreted as part of an SQL statement.
    Because it's not treated as SQL, the user input can't inject malicious SQL. Instead of using
    concatenation to include the user input, use this selection clause:
</p>
<pre>
// Constructs a selection clause with a replaceable parameter
String mSelectionClause =  "var = ?";
</pre>
<p>
    Set up the array of selection arguments like this:
</p>
<pre>
// Defines an array to contain the selection arguments
String[] selectionArgs = {""};
</pre>
<p>
    Put a value in the selection arguments array like this:
</p>
<pre>
// Sets the selection argument to the user's input
selectionArgs[0] = mUserInput;
</pre>
<p>
    A selection clause that uses <code>?</code> as a replaceable parameter and an array of
    selection arguments array are preferred way to specify a selection, even if the provider isn't
    based on an SQL database.
</p>
<!-- Displaying the results -->
<h3 id="DisplayResults">Displaying query results</h3>
<p>
    The {@link android.content.ContentResolver#query ContentResolver.query()} client method always 
    returns a {@link android.database.Cursor} containing the columns specified by the query's 
    projection for the rows that match the query's selection criteria. A 
    {@link android.database.Cursor} object provides random read access to the rows and columns it 
    contains. Using {@link android.database.Cursor} methods, you can iterate over the rows in the 
    results, determine the data type of each column, get the data out of a column, and examine other
    properties of the results. Some {@link android.database.Cursor} implementations automatically 
    update the object when the provider's data changes, or trigger methods in an observer object 
    when the {@link android.database.Cursor} changes, or both.
</p>
<p class="note">
    <strong>Note:</strong> A provider may restrict access to columns based on the nature of the
    object making the query. For example, the Contacts Provider restricts access for some columns to
    sync adapters, so it won't return them to an activity or service.
</p>
<p>
    If no rows match the selection criteria, the provider
    returns a {@link android.database.Cursor} object for which
    {@link android.database.Cursor#getCount Cursor.getCount()} is 0 (an empty cursor).
</p>
<p>
    If an internal error occurs, the results of the query depend on the particular provider. It may
    choose to return <code>null</code>, or it may throw an {@link java.lang.Exception}.
</p>
<p>
    Since a {@link android.database.Cursor} is a "list" of rows, a good way to display the
    contents of a {@link android.database.Cursor} is to link it to a {@link android.widget.ListView}
    via a {@link android.widget.SimpleCursorAdapter}.
</p>
<p>
    The following snippet continues the code from the previous snippet. It creates a
    {@link android.widget.SimpleCursorAdapter} object containing the {@link android.database.Cursor}
    retrieved by the query, and sets this object to be the adapter for a
    {@link android.widget.ListView}:
</p>
<pre class="prettyprint">
// Defines a list of columns to retrieve from the Cursor and load into an output row
String[] mWordListColumns =
{
    UserDictionary.Words.WORD,   // Contract class constant containing the word column name
    UserDictionary.Words.LOCALE  // Contract class constant containing the locale column name
};

// Defines a list of View IDs that will receive the Cursor columns for each row
int[] mWordListItems = { R.id.dictWord, R.id.locale};

// Creates a new SimpleCursorAdapter
mCursorAdapter = new SimpleCursorAdapter(
    getApplicationContext(),               // The application's Context object
    R.layout.wordlistrow,                  // A layout in XML for one row in the ListView
    mCursor,                               // The result from the query
    mWordListColumns,                      // A string array of column names in the cursor
    mWordListItems,                        // An integer array of view IDs in the row layout
    0);                                    // Flags (usually none are needed)

// Sets the adapter for the ListView
mWordList.setAdapter(mCursorAdapter);
</pre>
<p class="note">
    <strong>Note:</strong> To back a {@link android.widget.ListView} with a
    {@link android.database.Cursor}, the cursor must contain a column named <code>_ID</code>.
    Because of this, the query shown previously retrieves the <code>_ID</code> column for the
    "words" table, even though the {@link android.widget.ListView} doesn't display it.
    This restriction also explains why most providers have a <code>_ID</code> column for each of
    their tables.
</p>

        <!-- Getting data from query results -->
<h3 id="GettingResults">Getting data from query results</h3>
<p>
    Rather than simply displaying query results, you can use them for other tasks. For
    example, you can retrieve spellings from the user dictionary and then look them up in
    other providers. To do this, you iterate over the rows in the {@link android.database.Cursor}:
</p>
<pre class="prettyprint">

// Determine the column index of the column named "word"
int index = mCursor.getColumnIndex(UserDictionary.Words.WORD);

/*
 * Only executes if the cursor is valid. The User Dictionary Provider returns null if
 * an internal error occurs. Other providers may throw an Exception instead of returning null.
 */

if (mCursor != null) {
    /*
     * Moves to the next row in the cursor. Before the first movement in the cursor, the
     * "row pointer" is -1, and if you try to retrieve data at that position you will get an
     * exception.
     */
    while (mCursor.moveToNext()) {

        // Gets the value from the column.
        newWord = mCursor.getString(index);

        // Insert code here to process the retrieved word.

        ...

        // end of while loop
    }
} else {

    // Insert code here to report an error if the cursor is null or the provider threw an exception.
}
</pre>
<p>
    {@link android.database.Cursor} implementations contain several "get" methods for
    retrieving different types of data from the object. For example, the previous snippet
    uses {@link android.database.Cursor#getString getString()}. They also have a
    {@link android.database.Cursor#getType getType()} method that returns a value indicating
    the data type of the column.
</p>


    <!-- Requesting permissions -->
<h2 id="Permissions">Content Provider Permissions</h2>
<p>
    A provider's application can specify permissions that other applications must have in order to
    access the provider's data. These permissions ensure that the user knows what data
    an application will try to access. Based on the provider's requirements, other applications
    request the permissions they need in order to access the provider. End users see the requested
    permissions when they install the application.
</p>
<p>
    If a provider's application doesn't specify any permissions, then other applications have no
    access to the provider's data. However, components in the provider's application always have
    full read and write access, regardless of the specified permissions.
</p>
<p>
    As noted previously, the User Dictionary Provider requires the
    <code>android.permission.READ_USER_DICTIONARY</code> permission to retrieve data from it.
    The provider has the separate <code>android.permission.WRITE_USER_DICTIONARY</code>
    permission for inserting, updating, or deleting data.
</p>
<p>
    To get the permissions needed to access a provider, an application requests them with a
<code><a href="{@docRoot}guide/topics/manifest/uses-permission-element.html">&lt;uses-permission&gt;</a></code>
    element in its manifest file. When the Android Package Manager installs the application, a user 
    must approve all of the permissions the application requests. If the user approves all of them, 
    Package Manager continues the installation; if the user doesn't approve them, Package Manager
    aborts the installation.
</p>
<p>
    The following
<code><a href="{@docRoot}guide/topics/manifest/uses-permission-element.html">&lt;uses-permission&gt;</a></code> 
    element requests read access to the User Dictionary Provider:
</p>
<pre>
    &lt;uses-permission android:name="android.permission.READ_USER_DICTIONARY"&gt;
</pre>
<p>
    The impact of permissions on provider access is explained in more detail in the
    <a href="{@docRoot}guide/topics/security/security.html">Security and Permissions</a> guide.
</p>


<!-- Inserting, Updating, and Deleting Data -->
<h2 id="Modifications">Inserting, Updating, and Deleting Data</h2>
<p>
    In the same way that you retrieve data from a provider, you also use the interaction between
    a provider client and the provider's {@link android.content.ContentProvider} to modify data.
    You call a method of {@link android.content.ContentResolver} with arguments that are passed to
    the corresponding method of {@link android.content.ContentProvider}. The provider and provider
    client automatically handle security and inter-process communication.
</p>
<h3 id="Inserting">Inserting data</h3>
<p>
    To insert data into a provider, you call the
    {@link android.content.ContentResolver#insert ContentResolver.insert()}
    method. This method inserts a new row into the provider and returns a content URI for that row.
    This snippet shows how to insert a new word into the User Dictionary Provider:
</p>
<pre class="prettyprint">
// Defines a new Uri object that receives the result of the insertion
Uri mNewUri;

...

// Defines an object to contain the new values to insert
ContentValues mNewValues = new ContentValues();

/*
 * Sets the values of each column and inserts the word. The arguments to the "put"
 * method are "column name" and "value"
 */
mNewValues.put(UserDictionary.Words.APP_ID, "example.user");
mNewValues.put(UserDictionary.Words.LOCALE, "en_US");
mNewValues.put(UserDictionary.Words.WORD, "insert");
mNewValues.put(UserDictionary.Words.FREQUENCY, "100");

mNewUri = getContentResolver().insert(
    UserDictionary.Word.CONTENT_URI,   // the user dictionary content URI
    mNewValues                          // the values to insert
);
</pre>
<p>
    The data for the new row goes into a single {@link android.content.ContentValues} object, which
    is similar in form to a one-row cursor. The columns in this object don't need to have the
    same data type, and if you don't want to specify a value at all, you can set a column
    to <code>null</code> using {@link android.content.ContentValues#putNull ContentValues.putNull()}.
</p>
<p>
    The snippet doesn't add the <code>_ID</code> column, because this column is maintained
    automatically. The provider assigns a unique value of <code>_ID</code> to every row that is
    added. Providers usually use this value as the table's primary key.
</p>
<p>
    The content URI returned in <code>newUri</code> identifies the newly-added row, with
    the following format:
</p>
<pre>
content://user_dictionary/words/&lt;id_value&gt;
</pre>
<p>
    The <code>&lt;id_value&gt;</code> is the contents of <code>_ID</code> for the new row.
    Most providers can detect this form of content URI automatically and then perform the requested
    operation on that particular row.
</p>
<p>
    To get the value of <code>_ID</code> from the returned {@link android.net.Uri}, call
    {@link android.content.ContentUris#parseId ContentUris.parseId()}.
</p>
<h3 id="Updating">Updating data</h3>
<p>
    To update a row, you use a {@link android.content.ContentValues} object with the updated
    values just as you do with an insertion, and selection criteria just as you do with a query.
    The client method you use is
    {@link android.content.ContentResolver#update ContentResolver.update()}. You only need to add 
    values to the {@link android.content.ContentValues} object for columns you're updating. If you 
    want to clear the contents of a column, set the value to <code>null</code>.
</p>
<p>
    The following snippet changes all the rows whose locale has the language "en" to a
    have a locale of <code>null</code>. The return value is the number of rows that were updated:
</p>
<pre>
// Defines an object to contain the updated values
ContentValues mUpdateValues = new ContentValues();

// Defines selection criteria for the rows you want to update
String mSelectionClause = UserDictionary.Words.LOCALE +  "LIKE ?";
String[] mSelectionArgs = {"en_%"};

// Defines a variable to contain the number of updated rows
int mRowsUpdated = 0;

...

/*
 * Sets the updated value and updates the selected words.
 */
mUpdateValues.putNull(UserDictionary.Words.LOCALE);

mRowsUpdated = getContentResolver().update(
    UserDictionary.Words.CONTENT_URI,   // the user dictionary content URI
    mUpdateValues                       // the columns to update
    mSelectionClause                    // the column to select on
    mSelectionArgs                      // the value to compare to
);
</pre>
<p>
    You should also sanitize user input when you call
    {@link android.content.ContentResolver#update ContentResolver.update()}. To learn more about 
    this, read the section <a href="#Injection">Protecting against malicious input</a>.
</p>
<h3 id="Deleting">Deleting data</h3>
<p>
    Deleting rows is similar to retrieving row data: you specify selection criteria for the rows
    you want to delete and the client method returns the number of deleted rows.
    The following snippet deletes rows whose appid matches "user". The method returns the
    number of deleted rows.
</p>
<pre>

// Defines selection criteria for the rows you want to delete
String mSelectionClause = UserDictionary.Words.APP_ID + " LIKE ?";
String[] mSelectionArgs = {"user"};

// Defines a variable to contain the number of rows deleted
int mRowsDeleted = 0;

...

// Deletes the words that match the selection criteria
mRowsDeleted = getContentResolver().delete(
    UserDictionary.Words.CONTENT_URI,   // the user dictionary content URI
    mSelectionClause                    // the column to select on
    mSelectionArgs                      // the value to compare to
);
</pre>
<p>
    You should also sanitize user input when you call
    {@link android.content.ContentResolver#delete ContentResolver.delete()}. To learn more about 
    this, read the section <a href="#Injection">Protecting against malicious input</a>.
</p>
<!-- Provider Data Types -->
<h2 id="DataTypes">Provider Data Types</h2>
<p>
    Content providers can offer many different data types. The User Dictionary Provider offers only
    text, but providers can also offer the following formats:
</p>
    <ul>
        <li>
            integer
        </li>
        <li>
            long integer (long)
        </li>
        <li>
            floating point
        </li>
        <li>
            long floating point (double)
        </li>
    </ul>
<p>
    Another data type that providers often use is Binary Large OBject (BLOB) implemented as a
    64KB byte array. You can see the available data types by looking at the
    {@link android.database.Cursor} class "get" methods.
</p>
<p>
    The data type for each column in a provider is usually listed in its documentation.
    The data types for the User Dictionary Provider are listed in the reference documentation
    for its contract class {@link android.provider.UserDictionary.Words} (contract classes are
    described in the section <a href="#ContractClasses">Contract Classes</a>).
    You can also determine the data type by calling {@link android.database.Cursor#getType
    Cursor.getType()}.
</p>
<p>
    Providers also maintain MIME data type information for each content URI they define. You can
    use the MIME type information to find out if your application can handle data that the
    provider offers, or to choose a type of handling based on the MIME type. You usually need the
    MIME type when you are working with a provider that contains complex
    data structures or files. For example, the {@link android.provider.ContactsContract.Data}
    table in the Contacts Provider uses MIME types to label the type of contact data stored in each
    row. To get the MIME type corresponding to a content URI, call
    {@link android.content.ContentResolver#getType ContentResolver.getType()}.
</p>
<p>
    The section <a href="#MIMETypeReference">MIME Type Reference</a> describes the
    syntax of both standard and custom MIME types.
</p>


<!-- Alternative Forms of Provider Access -->
<h2 id="AltForms">Alternative Forms of Provider Access</h2>
<p>
    Three alternative forms of provider access are important in application development:
</p>
<ul>
    <li>
        <a href="#Batch">Batch access</a>: You can create a batch of access calls with methods in
        the {@link android.content.ContentProviderOperation} class, and then apply them with
        {@link android.content.ContentResolver#applyBatch ContentResolver.applyBatch()}.
    </li>
    <li>
        Asynchronous queries: You should do queries in a separate thread. One way to do this is to
        use a {@link android.content.CursorLoader} object. The examples in the
        <a href="{@docRoot}guide/components/loaders.html">Loaders</a> guide demonstrate
        how to do this.
    </li>
    <li>
        <a href="#Intents">Data access via intents</a>: Although you can't send an intent
        directly to a provider, you can send an intent to the provider's application, which is
        usually the best-equipped to modify the provider's data.
    </li>
</ul>
<p>
    Batch access and modification via intents are described in the following sections.
</p>
<h3 id="Batch">Batch access</h3>
<p>
    Batch access to a provider is useful for inserting a large number of rows, or for inserting
    rows in multiple tables in the same method call, or in general for performing a set of
    operations across process boundaries as a transaction (an atomic operation).
</p>
<p>
    To access a provider in "batch mode",
    you create an array of {@link android.content.ContentProviderOperation} objects and then
    dispatch them to a content provider with
    {@link android.content.ContentResolver#applyBatch ContentResolver.applyBatch()}. You pass the 
    content provider's <em>authority</em> to this  method, rather than a particular content URI. 
    This allows each {@link android.content.ContentProviderOperation} object in the array to work 
    against a different table. A call to {@link android.content.ContentResolver#applyBatch
    ContentResolver.applyBatch()} returns an array of results.
</p>
<p>
    The description of the {@link android.provider.ContactsContract.RawContacts} contract class
    includes a code snippet that demonstrates batch insertion. The
    <a href="{@docRoot}resources/samples/ContactManager/index.html">Contact Manager</a>
    sample application contains an example of batch access in its <code>ContactAdder.java</code>
    source file.
</p>
<div class="sidebox-wrapper">
<div class="sidebox">
<h2>Displaying data using a helper app</h2>
<p>
    If your application <em>does</em> have access permissions, you still may want to use an
    intent to display data in another application. For example, the Calendar application accepts an
    {@link android.content.Intent#ACTION_VIEW} intent, which displays a particular date or event.
    This allows you to display calendar information without having to create your own UI.
    To learn more about this feature, see the
    <a href="{@docRoot}guide/topics/providers/calendar-provider.html">Calendar Provider</a> guide.
</p>
<p>
    The application to which you send the intent doesn't have to be the application
    associated with the provider. For example, you can retrieve a contact from the
    Contact Provider, then send an {@link android.content.Intent#ACTION_VIEW} intent
    containing the content URI for the contact's image to an image viewer.
</p>
</div>
</div>
<h3 id="Intents">Data access via intents</h3>
<p>
    Intents can provide indirect access to a content provider. You allow the user to access
    data in a provider even if your application doesn't have access permissions, either by
    getting a result intent back from an application that has permissions, or by activating an
    application that has permissions and letting the user do work in it.
</p>
<h4>Getting access with temporary permissions</h4>
<p>
    You can access data in a content provider, even if you don't have the proper access
    permissions, by sending an intent to an application that does have the permissions and
    receiving back a result intent containing "URI" permissions.
    These are permissions for a specific content URI that last until the activity that receives
    them is finished. The application that has permanent permissions grants temporary
    permissions by setting a flag in the result intent:
</p>
<ul>
    <li>
        <strong>Read permission:</strong>
        {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION}
    </li>
    <li>
        <strong>Write permission:</strong>
        {@link android.content.Intent#FLAG_GRANT_WRITE_URI_PERMISSION}
    </li>
</ul>
<p class="note">
    <strong>Note:</strong> These flags don't give general read or write access to the provider
    whose authority is contained in the content URI. The access is only for the URI itself.
</p>
<p>
    A provider defines URI permissions for content URIs in its manifest, using the
<code><a href="{@docRoot}guide/topics/manifest/provider-element.html#gprmsn">android:grantUriPermission</a></code>
    attribute of the 
<code><a href="{@docRoot}guide/topics/manifest/provider-element.html">&lt;provider&gt;</a></code>
    element, as well as the
<code><a href="{@docRoot}guide/topics/manifest/grant-uri-permission-element.html">&lt;grant-uri-permission&gt;</a></code>
    child element of the
<code><a href="{@docRoot}guide/topics/manifest/provider-element.html">&lt;provider&gt;</a></code>
    element. The URI permissions mechanism is explained in more detail in the
    <a href="{@docRoot}guide/topics/security/security.html">Security and Permissions</a> guide,
    in the section "URI Permissions".
</p>
<p>
    For example, you can retrieve data for a contact in the Contacts Provider, even if you don't
    have the {@link android.Manifest.permission#READ_CONTACTS} permission. You might want to do
    this in an application that sends e-greetings to a contact on his or her birthday. Instead of
    requesting {@link android.Manifest.permission#READ_CONTACTS}, which gives you access to all of
    the user's contacts and all of their information, you prefer to let the user control which
    contacts are used by your application. To do this, you use the following process:
</p>
<ol>
    <li>
        Your application sends an intent containing the action
        {@link android.content.Intent#ACTION_PICK} and the "contacts" MIME type
        {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE}, using the
        method {@link android.app.Activity#startActivityForResult
        startActivityForResult()}.
    </li>
    <li>
        Because this intent matches the intent filter for the
        People app's "selection" activity, the activity will come to the foreground.
    </li>
    <li>
        In the selection activity, the user selects a
        contact to update. When this happens, the selection activity calls
        {@link android.app.Activity#setResult setResult(resultcode, intent)}
        to set up a intent to give back to your application. The intent contains the content URI
        of the contact the user selected, and the "extras" flags
        {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION}. These flags grant URI
        permission to your app to read data for the contact pointed to by the
        content URI. The selection activity then calls {@link android.app.Activity#finish()} to
        return control to your application.
    </li>
    <li>
        Your activity returns to the foreground, and the system calls your activity's
        {@link android.app.Activity#onActivityResult onActivityResult()}
        method. This method receives the result intent created by the selection activity in
        the People app.
    </li>
    <li>
        With the content URI from the result intent, you can read the contact's data
        from the Contacts Provider, even though you didn't request permanent read access permission
        to the provider in your manifest. You can then get the contact's birthday information
        or his or her email address and then send the e-greeting.
    </li>
</ol>
<h4>Using another application</h4>
<p>
    A simple way to allow the user to modify data to which you don't have access permissions is to
    activate an application that has permissions and let the user do the work there.
</p>
<p>
    For example, the Calendar application accepts an
    {@link android.content.Intent#ACTION_INSERT} intent, which allows you to activate the
    application's insert UI. You can pass "extras" data in this intent, which the application
    uses to pre-populate the UI. Because recurring events have a complex syntax, the preferred
    way of inserting events into the Calendar Provider is to activate the Calendar app with an
    {@link android.content.Intent#ACTION_INSERT} and then let the user insert the event there.
</p>
<!-- Contract Classes -->
<h2 id="ContractClasses">Contract Classes</h2>
<p>
    A contract class defines constants that help applications work with the content URIs, column
    names, intent actions, and other features of a content provider. Contract classes are not
    included automatically with a provider; the provider's developer has to define them and then
    make them available to other developers. Many of the providers included with the Android
    platform have corresponding contract classes in the package {@link android.provider}.
</p>
<p>
    For example, the User Dictionary Provider has a contract class
    {@link android.provider.UserDictionary} containing content URI and column name constants. The
    content URI for the "words" table is defined in the constant
    {@link android.provider.UserDictionary.Words#CONTENT_URI UserDictionary.Words.CONTENT_URI}.
    The {@link android.provider.UserDictionary.Words} class also contains column name constants,
    which are used in the example snippets in this guide. For example, a query projection can be
    defined as:
</p>
<pre>
String[] mProjection =
{
    UserDictionary.Words._ID,
    UserDictionary.Words.WORD,
    UserDictionary.Words.LOCALE
};
</pre>
<p>
    Another contract class is {@link android.provider.ContactsContract} for the Contacts Provider.
    The reference documentation for this class includes example code snippets. One of its
    subclasses, {@link android.provider.ContactsContract.Intents.Insert}, is a contract
    class that contains constants for intents and intent data.
</p>


<!-- MIME Type Reference -->
<h2 id="MIMETypeReference">MIME Type Reference</h2>
<p>
    Content providers can return standard MIME media types, or custom MIME type strings, or both.
</p>
<p>
    MIME types have the format
</p>
<pre>
<em>type</em>/<em>subtype</em>
</pre>
<p>
    For example, the well-known MIME type <code>text/html</code> has the <code>text</code> type and
    the <code>html</code> subtype. If the provider returns this type for a URI, it means that a
    query using that URI will return text containing HTML tags.
</p>
<p>
    Custom MIME type strings, also called "vendor-specific" MIME types, have more
    complex <em>type</em> and <em>subtype</em> values. The <em>type</em> value is always
</p>
<pre>
vnd.android.cursor.<strong>dir</strong>
</pre>
<p>
    for multiple rows, or
</p>
<pre>
vnd.android.cursor.<strong>item</strong>
</pre>
<p>
    for a single row.
</p>
<p>
    The <em>subtype</em> is provider-specific. The Android built-in providers usually have a simple
    subtype. For example, the when the Contacts application creates a row for a telephone number,
    it sets the following MIME type in the row:
</p>
<pre>
vnd.android.cursor.item/phone_v2
</pre>
<p>
    Notice that the subtype value is simply <code>phone_v2</code>.
</p>
<p>
    Other provider developers may create their own pattern of subtypes based on the provider's
    authority and table names. For example, consider a provider that contains train timetables.
    The provider's authority is <code>com.example.trains</code>, and it contains the tables
    Line1, Line2, and Line3. In response to the content URI
</p>
<p>
<pre>
content://com.example.trains/Line1
</pre>
<p>
    for table Line1, the provider returns the MIME type
</p>
<pre>
vnd.android.cursor.<strong>dir</strong>/vnd.example.line1
</pre>
<p>
     In response to the content URI
</p>
<pre>
content://com.example.trains/Line2/5
</pre>
<p>
    for row 5 in table Line2, the provider returns the MIME type
</p>
<pre>
vnd.android.cursor.<strong>item</strong>/vnd.example.line2
</pre>
<p>
    Most content providers define contract class constants for the MIME types they use. The
    Contacts Provider contract class {@link android.provider.ContactsContract.RawContacts},
    for example, defines the constant
    {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE} for the MIME type of
    a single raw contact row.
</p>
<p>
    Content URIs for single rows are described in the section
    <a href="#ContentURIs">Content URIs</a>.
</p>