training/beam-files/receive-files.jd

page.title=Receiving Files from Another Device

trainingnavtop=true
@jd:body

<div id="tb-wrapper">
<div id="tb">

<h2>This lesson teaches you to</h2>
<ol>
    <li><a href="#IntentFilter">Respond to a Request to Display Data</a></li>
    <li><a href="#RequestPermissions">Request File Permissions</a></li>
    <li><a href="#GetFilePath">Get the Directory for Copied Files</a></li>
</ol>
<h2>You should also read</h2>
<ul>
    <li>
        <a href="{@docRoot}guide/topics/providers/content-provider-basics.html#ContentURIs"
        >Content URIs</a>
    </li>
    <li>
        <a href="{@docRoot}guide/components/intents-filters.html">Intents and Intent Filters</a>
    </li>
    <li>
        <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html">Notifications</a>
    </li>
    <li>
        <a href="{@docRoot}guide/topics/data/data-storage.html#filesExternal"
        >Using the External Storage</a>
    </li>
</ul>

</div>
</div>

<p>
    Android Beam file transfer copies files to a special directory on the receiving device. It also
    scans the copied files using the Android Media Scanner and adds entries for media files to
    the {@link android.provider.MediaStore} provider. This lesson shows you how to respond when the
    file copy is complete, and how to locate the copied files on the receiving device.
</p>
<h2 id="IntentFilter">Respond to a Request to Display Data</h2>
<p>
    When Android Beam file transfer finishes copying files to the receiving device, it posts a
    notification containing an {@link android.content.Intent} with the action
    {@link android.content.Intent#ACTION_VIEW ACTION_VIEW}, the MIME type of the first file that
    was transferred, and a URI that points to the first file. When the user clicks the notification,
    this intent is sent out to the system. To have your app respond to this intent, add an
    <code><a href="{@docRoot}guide/topics/manifest/intent-filter-element.html"
    >&lt;intent-filter&gt;</a></code> element for the
    <code><a href="{@docRoot}guide/topics/manifest/activity-element.html"
    >&lt;activity&gt;</a></code> element of the {@link android.app.Activity} that should respond.
    In the <code><a href="{@docRoot}guide/topics/manifest/intent-filter-element.html"
    >&lt;intent-filter&gt;</a></code> element, add the following child elements:
</p>
<dl>
    <dt>
        <code><a href="{@docRoot}guide/topics/manifest/action-element.html"
        >&lt;action android:name="android.intent.action.VIEW" /&gt;</a></code>
    </dt>
    <dd>
        Matches the {@link android.content.Intent#ACTION_VIEW ACTION_VIEW} intent sent from the
        notification.
    </dd>
    <dt>
        <code><a href="{@docRoot}guide/topics/manifest/category-element.html"
        >&lt;category android:name="android.intent.category.CATEGORY_DEFAULT" /&gt;</a></code>
    </dt>
    <dd>
        Matches an {@link android.content.Intent} that doesn't have an explicit category.
    </dd>
    <dt>
        <code><a href="{@docRoot}guide/topics/manifest/data-element.html"
        >&lt;data android:mimeType="<i>mime-type</i>" /&gt;</a></code>
    </dt>
    <dd>
        Matches a MIME type. Specify only those MIME types that your app can handle.
    </dd>
</dl>
<p>
    For example, the following snippet shows you how to add an intent filter that
    triggers the activity <code>com.example.android.nfctransfer.ViewActivity</code>:
</p>
<pre>
    &lt;activity
        android:name="com.example.android.nfctransfer.ViewActivity"
        android:label="Android Beam Viewer" &gt;
        ...
        &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.VIEW"/&gt;
            &lt;category android:name="android.intent.category.DEFAULT"/&gt;
            ...
        &lt;/intent-filter&gt;
    &lt;/activity&gt;
</pre>
<p class="note">
    <strong>Note:</strong> Android Beam file transfer is not the only source of an
    {@link android.content.Intent#ACTION_VIEW ACTION_VIEW} intent. Other apps on the receiving
    device can also send an {@link android.content.Intent} with this action.
    Handling this situation is discussed in the section <a href="#GetDirectory"
    >Get the directory from a content URI</a>.
</p>
<h2 id="RequestPermissions">Request File Permissions</h2>
<p>
    To read files that Android Beam file transfer copies to the device, request the permission
    {@link android.Manifest.permission#READ_EXTERNAL_STORAGE READ_EXTERNAL_STORAGE}. For example:
</p>
<pre>
    &lt;uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /&gt;</pre>
<p>
    If you want to copy transferred files to your app's own storage area, request the permission
    {@link android.Manifest.permission#WRITE_EXTERNAL_STORAGE WRITE_EXTERNAL_STORAGE} instead.
    {@link android.Manifest.permission#WRITE_EXTERNAL_STORAGE WRITE_EXTERNAL_STORAGE} includes
    {@link android.Manifest.permission#READ_EXTERNAL_STORAGE READ_EXTERNAL_STORAGE}.
</p>
<p class="note">
    <strong>Note:</strong> As of Android 4.2.2 (API level 17), the permission
    {@link android.Manifest.permission#READ_EXTERNAL_STORAGE READ_EXTERNAL_STORAGE} is
    only enforced if the user chooses to do so. Future versions of the platform may require this
    permission in all cases. To ensure forward compatibility, request the permission now, before it
    becomes required.
</p>
<p>
    Since your app has control over its internal storage area, you don't need to request
    write permission to copy a transferred file to your internal storage area.
</p>
<h2 id="GetFilePath">Get the Directory for Copied Files</h2>
<p>
    Android Beam file transfer copies all the files in a single transfer to one directory
    on the receiving device. The URI in the content {@link android.content.Intent} sent by the
    Android Beam file transfer notification points to the first transferred file. However, your
    app may also receive an {@link android.content.Intent#ACTION_VIEW ACTION_VIEW} intent from a
    source other than Android Beam file transfer. To determine how you should handle the incoming
    {@link android.content.Intent}, you need to examine its scheme and authority.
</p>
<p>
    To get the scheme for the URI, call {@link android.net.Uri#getScheme() Uri.getScheme()}. The
    following code snippet shows you how to determine the scheme and handle the URI accordingly:
</p>
<pre>
public class MainActivity extends Activity {
    ...
    // A File object containing the path to the transferred files
    private File mParentPath;
    // Incoming Intent
    private Intent mIntent;
    ...
    /*
     * Called from onNewIntent() for a SINGLE_TOP Activity
     * or onCreate() for a new Activity. For onNewIntent(),
     * remember to call setIntent() to store the most
     * current Intent
     *
     */
    private void handleViewIntent() {
        ...
        // Get the Intent action
        mIntent = getIntent();
        String action = mIntent.getAction();
        /*
         * For ACTION_VIEW, the Activity is being asked to display data.
         * Get the URI.
         */
        if (TextUtils.equals(action, Intent.ACTION_VIEW)) {
            // Get the URI from the Intent
            Uri beamUri = mIntent.getData();
            /*
             * Test for the type of URI, by getting its scheme value
             */
            if (TextUtils.equals(beamUri.getScheme(), "file")) {
                mParentPath = handleFileUri(beamUri);
            } else if (TextUtils.equals(
                    beamUri.getScheme(), "content")) {
                mParentPath = handleContentUri(beamUri);
            }
        }
        ...
    }
    ...
}
</pre>
<h3>Get the directory from a file URI</h3>
<p>
    If the incoming {@link android.content.Intent} contains a file URI, the URI contains the
    absolute file name of a file, including the full directory path and file name. For Android Beam
    file transfer, the directory path points to the location of the other transferred files, if
    any. To get the directory path, get the path part of the URI, which contains all of the URI
    except the <code>file:</code> prefix. Create a {@link java.io.File} from the path part, then
    get the parent path of the {@link java.io.File}:
</p>
<pre>
    ...
    public String handleFileUri(Uri beamUri) {
        // Get the path part of the URI
        String fileName = beamUri.getPath();
        // Create a File object for this filename
        File copiedFile = new File(fileName);
        // Get a string containing the file's parent directory
        return copiedFile.getParent();
    }
    ...
</pre>

<h3 id="GetDirectory">Get the directory from a content URI</h3>
<p>
    If the incoming {@link android.content.Intent} contains a content URI, the URI may point to a
    directory and file name stored in the {@link android.provider.MediaStore} content provider. You
    can detect a content URI for {@link android.provider.MediaStore} by testing the URI's
    authority value. A content URI for {@link android.provider.MediaStore} may come from
    Android Beam file transfer or from another app, but in both cases you can retrieve a directory
    and file name for the content URI.
</p>
<p>
    You can also receive an incoming {@link android.content.Intent#ACTION_VIEW ACTION_VIEW}
    intent containing a content URI for a content provider other than
    {@link android.provider.MediaStore}. In this case, the content URI doesn't contain the
    {@link android.provider.MediaStore} authority value, and the content URI usually doesn't point
    to a directory.
</p>
<p class="note">
    <strong>Note:</strong> For Android Beam file transfer, you receive a content URI in the
    {@link android.content.Intent#ACTION_VIEW ACTION_VIEW} intent if the first incoming file
    has a MIME type of "audio/*", "image/*", or "video/*", indicating that the file is media-
    related. Android Beam file transfer indexes the media files it transfers by running Media
    Scanner on the directory where it stores transferred files. Media Scanner writes its results
    to the {@link android.provider.MediaStore} content provider, then it passes a content URI
    for the first file back to Android Beam file transfer. This content URI is the one you
    receive in the notification {@link android.content.Intent}. To get the directory
    of the first file, you retrieve it from {@link android.provider.MediaStore} using the content
    URI.
</p>
<h3>Determine the content provider</h3>
<p>
    To determine if you can retrieve a file directory from the content URI, determine the
    the content provider associated with the URI by calling
    {@link android.net.Uri#getAuthority Uri.getAuthority()} to get the URI's authority. The
    result has two possible values:
</p>
<dl>
    <dt>
        {@link android.provider.MediaStore#AUTHORITY MediaStore.AUTHORITY}
    </dt>
    <dd>
        The URI is for a file or files tracked by {@link android.provider.MediaStore}. Retrieve the
        full file name from {@link android.provider.MediaStore}, and get directory from the file
        name.
    </dd>
    <dt>
        Any other authority value
    </dt>
    <dd>
        A content URI from another content provider. Display the data associated with the content
        URI, but don't get the file directory.
    </dd>
</dl>
<p>
    To get the directory for a {@link android.provider.MediaStore} content URI,
    run a query that specifies the incoming content URI for the {@link android.net.Uri} argument and
    the column {@link android.provider.MediaStore.MediaColumns#DATA MediaColumns.DATA} for the
    projection. The returned {@link android.database.Cursor} contains the full path and name for
    the file represented by the URI. This path also contains all the other files that Android Beam
    file transfer just copied to the device.
</p>
<p>
    The following snippet shows you how to test the authority of the content URI and retrieve the
    the path and file name for the transferred file:
</p>
<pre>
    ...
    public String handleContentUri(Uri beamUri) {
        // Position of the filename in the query Cursor
        int filenameIndex;
        // File object for the filename
        File copiedFile;
        // The filename stored in MediaStore
        String fileName;
        // Test the authority of the URI
        if (!TextUtils.equals(beamUri.getAuthority(), MediaStore.AUTHORITY)) {
            /*
             * Handle content URIs for other content providers
             */
        // For a MediaStore content URI
        } else {
            // Get the column that contains the file name
            String[] projection = { MediaStore.MediaColumns.DATA };
            Cursor pathCursor =
                    getContentResolver().query(beamUri, projection,
                    null, null, null);
            // Check for a valid cursor
            if (pathCursor != null &amp;&amp;
                    pathCursor.moveToFirst()) {
                // Get the column index in the Cursor
                filenameIndex = pathCursor.getColumnIndex(
                        MediaStore.MediaColumns.DATA);
                // Get the full file name including path
                fileName = pathCursor.getString(filenameIndex);
                // Create a File object for the filename
                copiedFile = new File(fileName);
                // Return the parent directory of the file
                return new File(copiedFile.getParent());
             } else {
                // The query didn't work; return null
                return null;
             }
        }
    }
    ...
</pre>
<p>
    To learn more about retrieving data from a content provider, see the section
    <a href="{@docRoot}guide/topics/providers/content-provider-basics.html#SimpleQuery"
    >Retrieving Data from the Provider</a>.
</p>