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.
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
<intent-filter> element for the
<activity> element of the {@link android.app.Activity} that should respond.
In the <intent-filter> element, add the following child elements:
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.CATEGORY_DEFAULT" />
<data android:mimeType="mime-type" />
For example, the following snippet shows you how to add an intent filter that
triggers the activity com.example.android.nfctransfer.ViewActivity:
<activity
android:name="com.example.android.nfctransfer.ViewActivity"
android:label="Android Beam Viewer" >
...
<intent-filter>
<action android:name="android.intent.action.VIEW"/>
<category android:name="android.intent.category.DEFAULT"/>
...
</intent-filter>
</activity>
Note: 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 Get the directory from a content URI.
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:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
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}.
Note: 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.
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.
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.
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:
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);
}
}
...
}
...
}
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 file: prefix. Create a {@link java.io.File} from the path part, then
get the parent path of the {@link java.io.File}:
...
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();
}
...
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.
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.
Note: 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.
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:
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.
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:
...
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 &&
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;
}
}
}
...
To learn more about retrieving data from a content provider, see the section Retrieving Data from the Provider.