android_frameworks_base/docs/html/training/secure-file-sharing/share-file.jd

page.title=Sharing a File

trainingnavtop=true
@jd:body


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<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#ReceiveRequests">Receive File Requests</a></li>
  <li><a href="#CreateFileSelection">Create a File Selection Activity</a></li>
  <li><a href="#RespondToRequest">Respond to a File Selection</a></li>
  <li><a href="#GrantPermissions">Grant Permissions for the File</a></li>
  <li><a href="#ShareFile">Share the File with the Requesting App</a>
</ol>

<h2>You should also read</h2>
<ul>
    <li>
        <a href="{@docRoot}guide/topics/providers/content-provider-creating.html#ContentURI"
        >Designing Content URIs</a>
    </li>
    <li>
        <a href="{@docRoot}guide/topics/providers/content-provider-creating.html#Permissions"
        >Implementing Content Provider Permissions</a>
    </li>
    <li>
        <a href="{@docRoot}guide/topics/security/permissions.html">Permissions</a>
    </li>
    <li>
        <a href="{@docRoot}guide/components/intents-filters.html">Intents and Intent Filters</a>
    </li>
</ul>

</div>
</div>
<p>
    Once you have set up your app to share files using content URIs, you can respond to other apps'
    requests for those files. One way to respond to these requests is to provide a file selection
    interface from the server app that other applications can invoke. This approach allows a client
    application to let users select a file from the server app and then receive the selected file's
    content URI.
</p>
<p>
    This lesson shows you how to create a file selection {@link android.app.Activity} in your app
    that responds to requests for files.
</p>
<h2 id="ReceiveRequests">Receive File Requests</h2>
<p>
    To receive requests for files from client apps and respond with a content URI, your app should
    provide a file selection {@link android.app.Activity}. Client apps start this
    {@link android.app.Activity} by calling {@link android.app.Activity#startActivityForResult
    startActivityForResult()} with an {@link android.content.Intent} containing the action
    {@link android.content.Intent#ACTION_PICK ACTION_PICK}. When the client app calls
    {@link android.app.Activity#startActivityForResult startActivityForResult()}, your app can
    return a result to the client app, in the form of a content URI for the file the user selected.
</p>
<p>
    To learn how to implement a request for a file in a client app, see the lesson
    <a href="request-file.html">Requesting a Shared File</a>.
</p>
<h2 id="CreateFileSelection">Create a File Selection Activity</h2>
<p>
    To set up the file selection {@link android.app.Activity}, start by specifying the
    {@link android.app.Activity} in your manifest, along with an intent filter
    that matches the action {@link android.content.Intent#ACTION_PICK ACTION_PICK} and the
    categories {@link android.content.Intent#CATEGORY_DEFAULT CATEGORY_DEFAULT} and
    {@link android.content.Intent#CATEGORY_OPENABLE CATEGORY_OPENABLE}.  Also add MIME type filters
    for the files your app serves to other apps. The following snippet shows you how to specify the
    new {@link android.app.Activity} and intent filter:
</p>
<pre>
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"&gt;
    ...
        &lt;application&gt;
        ...
            &lt;activity
                android:name=".FileSelectActivity"
                android:label="&#64;"File Selector" &gt;
                &lt;intent-filter&gt;
                    &lt;action
                        android:name="android.intent.action.PICK"/&gt;
                    &lt;category
                        android:name="android.intent.category.DEFAULT"/&gt;
                    &lt;category
                        android:name="android.intent.category.OPENABLE"/&gt;
                    &lt;data android:mimeType="text/plain"/&gt;
                    &lt;data android:mimeType="image/*"/&gt;
                &lt;/intent-filter&gt;
            &lt;/activity&gt;</pre>
<h3>Define the file selection Activity in code</h3>
<p>
    Next, define an {@link android.app.Activity} subclass that displays the files available from
    your app's <code>files/images/</code> directory in internal storage and allows the user to pick
    the desired file. The following snippet demonstrates how to define this
    {@link android.app.Activity} and respond to the user's selection:
</p>
<pre>
public class MainActivity extends Activity {
    // The path to the root of this app's internal storage
    private File mPrivateRootDir;
    // The path to the "images" subdirectory
    private File mImagesDir;
    // Array of files in the images subdirectory
    File[] mImageFiles;
    // Array of filenames corresponding to mImageFiles
    String[] mImageFilenames;
    // Initialize the Activity
    &#64;Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        // Set up an Intent to send back to apps that request a file
        mResultIntent =
                new Intent("com.example.myapp.ACTION_RETURN_FILE");
        // Get the files/ subdirectory of internal storage
        mPrivateRootDir = getFilesDir();
        // Get the files/images subdirectory;
        mImagesDir = new File(mPrivateRootDir, "images");
        // Get the files in the images subdirectory
        mImageFiles = mImagesDir.listFiles();
        // Set the Activity's result to null to begin with
        setResult(Activity.RESULT_CANCELED, null);
        /*
         * Display the file names in the ListView mFileListView.
         * Back the ListView with the array mImageFilenames, which
         * you can create by iterating through mImageFiles and
         * calling File.getAbsolutePath() for each File
         */
         ...
    }
    ...
}</pre>
<h2 id="RespondToRequest">Respond to a File Selection</h2>
<p>
    Once a user selects a shared file, your application must determine what file was selected and
    then generate a content URI for the file. Since the {@link android.app.Activity} displays the
    list of available files in a {@link android.widget.ListView}, when the user clicks a file name
    the system calls the method {@link android.widget.AdapterView.OnItemClickListener#onItemClick
    onItemClick()}, in which you can get the selected file.
</p>
<p>
    In {@link android.widget.AdapterView.OnItemClickListener#onItemClick onItemClick()}, get a
    {@link java.io.File} object for the file name of the selected file and pass it as an argument to
    {@link android.support.v4.content.FileProvider#getUriForFile getUriForFile()}, along with the
    authority that you specified in the
    <code><a href="{@docRoot}guide/topics/manifest/provider-element.html"
    >&lt;provider&gt;</a></code> element for the {@link android.support.v4.content.FileProvider}.
    The resulting content URI contains the authority, a path segment corresponding to the file's
    directory (as specified in the XML meta-data), and the name of the file including its
    extension. How {@link android.support.v4.content.FileProvider} maps directories to path
    segments based on XML meta-data is described in the section
    <a href="setup-sharing.html#DefineMetaData">Specify Sharable Directories</a>.
</p>
<p>
    The following snippet shows you how to detect the selected file and get a content URI for it:
</p>
<pre>
    protected void onCreate(Bundle savedInstanceState) {
        ...
        // Define a listener that responds to clicks on a file in the ListView
        mFileListView.setOnItemClickListener(
                new AdapterView.OnItemClickListener() {
            &#64;Override
            /*
             * When a filename in the ListView is clicked, get its
             * content URI and send it to the requesting app
             */
            public void onItemClick(AdapterView&lt;?&gt; adapterView,
                    View view,
                    int position,
                    long rowId) {
                /*
                 * Get a File for the selected file name.
                 * Assume that the file names are in the
                 * mImageFilename array.
                 */
                File requestFile = new File(mImageFilename[position]);
                /*
                 * Most file-related method calls need to be in
                 * try-catch blocks.
                 */
                // Use the FileProvider to get a content URI
                try {
                    fileUri = FileProvider.getUriForFile(
                            MainActivity.this,
                            "com.example.myapp.fileprovider",
                            requestFile);
                } catch (IllegalArgumentException e) {
                    Log.e("File Selector",
                          "The selected file can't be shared: " +
                          clickedFilename);
                }
                ...
            }
        });
        ...
    }</pre>
<p>
    Remember that you can only generate content URIs for files that reside in a directory
    you've specified in the meta-data file that contains the <code>&lt;paths&gt;</code> element, as
    described in the section <a href="setup-sharing.html#DefineMetaData"
    >Specify Sharable Directories</a>. If you call
    {@link android.support.v4.content.FileProvider#getUriForFile getUriForFile()} for a
    {@link java.io.File} in a path that you haven't specified, you receive an
    {@link java.lang.IllegalArgumentException}.
</p>
<h2 id="GrantPermissions">Grant Permissions for the File</h2>
<p>
    Now that you have a content URI for the file you want to share with another app, you need to
    allow the client app to access the file. To allow access, grant permissions to the client app by
    adding the content URI to an {@link android.content.Intent} and then setting permission flags on
    the {@link android.content.Intent}. The permissions you grant are temporary and expire
    automatically when the receiving app's task stack is finished.
</p>
<p>
    The following code snippet shows you how to set read permission for the file:
</p>
<pre>
    protected void onCreate(Bundle savedInstanceState) {
        ...
        // Define a listener that responds to clicks in the ListView
        mFileListView.setOnItemClickListener(
                new AdapterView.OnItemClickListener() {
            &#64;Override
            public void onItemClick(AdapterView&lt;?&gt; adapterView,
                    View view,
                    int position,
                    long rowId) {
                ...
                if (fileUri != null) {
                    // Grant temporary read permission to the content URI
                    mResultIntent.addFlags(
                        Intent.FLAG_GRANT_READ_URI_PERMISSION);
                }
                ...
             }
             ...
        });
    ...
    }</pre>
<p class="caution">
    <strong>Caution:</strong> Calling {@link android.content.Intent#setFlags setFlags()} is the only
    way to securely grant access to your files using temporary access permissions. Avoid calling
    {@link android.content.Context#grantUriPermission Context.grantUriPermission()} method for a
    file's content URI, since this method grants access that you can only revoke by
    calling {@link android.content.Context#revokeUriPermission Context.revokeUriPermission()}.
</p>
<h2 id="ShareFile">Share the File with the Requesting App</h2>
<p>
    To share the file with the app that requested it, pass the {@link android.content.Intent}
    containing the content URI and permissions to {@link android.app.Activity#setResult
    setResult()}. When the {@link android.app.Activity} you have just defined is finished, the
    system sends the {@link android.content.Intent} containing the content URI to the client app.
    The following code snippet shows you how to do this:
</p>
<pre>
    protected void onCreate(Bundle savedInstanceState) {
        ...
        // Define a listener that responds to clicks on a file in the ListView
        mFileListView.setOnItemClickListener(
                new AdapterView.OnItemClickListener() {
            &#64;Override
            public void onItemClick(AdapterView&lt;?&gt; adapterView,
                    View view,
                    int position,
                    long rowId) {
                ...
                if (fileUri != null) {
                    ...
                    // Put the Uri and MIME type in the result Intent
                    mResultIntent.setDataAndType(
                            fileUri,
                            getContentResolver().getType(fileUri));
                    // Set the result
                    MainActivity.this.setResult(Activity.RESULT_OK,
                            mResultIntent);
                    } else {
                        mResultIntent.setDataAndType(null, "");
                        MainActivity.this.setResult(RESULT_CANCELED,
                                mResultIntent);
                    }
                }
        });</pre>
<p>
    Provide users with an way to return immediately to the client app once they have chosen a file.
    One way to do this is to provide a checkmark or <b>Done</b> button. Associate a method with
    the button using the button's
    <code><a href="{@docRoot}reference/android/view/View.html#attr_android:onClick"
    >android:onClick</a></code> attribute. In the method, call
    {@link android.app.Activity#finish finish()}. For example:
</p>
<pre>
    public void onDoneClick(View v) {
        // Associate a method with the Done button
        finish();
    }</pre>