FileProvider

FileProvider is a special subclass of ContentProvider that facilitates secure sharing of files associated with an app by creating a content://Uri for a file instead of a file:///Uri.

A content URI allows you to grant read and write access using temporary access permissions. When you create an Intent containing a content URI, in order to send the content URI to a client app, you can also call Intent.setFlags() to add permissions. These permissions are available to the client app for as long as the stack for a receiving Activity is active. For an Intent going to a Service, the permissions are available as long as the Service is running.

In comparison, to control access to a file:///Uri you have to modify the file system permissions of the underlying file. The permissions you provide become available to any app, and remain in effect until you change them. This level of access is fundamentally insecure.

The increased level of file access security offered by a content URI makes FileProvider a key part of Android's security infrastructure.

This overview of FileProvider includes the following topics:

1. Defining a FileProvider
2. Specifying Available Files
3. Generating the Content URI for a File
4. Granting Temporary Permissions to a URI
5. Serving a Content URI to Another App

Defining a FileProvider

Extend FileProvider with a default constructor:

public class MyFileProvider extends FileProvider {
   public MyFileProvider() {
       ...
   }
}

<manifest>
   ...
   <application>
       ...
       <provider
           android:name="com.sample.MyFileProvider"
           android:authorities="com.mydomain.fileprovider"
           android:exported="false"
           android:grantUriPermissions="true">
           ...
       </provider>
       ...
   </application>
</manifest>

It is possible to use FileProvider directly instead of extending it. However, this is not reliable and will causes crashes on some devices.

Specifying Available Files

A FileProvider can only generate a content URI for files in directories that you specify beforehand. To specify a directory, specify its storage area and path in XML, using child elements of the <paths> element. For example, the following paths element tells FileProvider that you intend to request content URIs for the images/ subdirectory of your private file area.

<paths xmlns:android="http://schemas.android.com/apk/res/android">
   <files-path name="my_images" path="images/"/>
   ...
</paths>

The <paths> element must contain one or more of the following child elements:

• <files-path name="name" path="path" />

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  Represents files in the files/ subdirectory of your app's internal storage area. This subdirectory is the same as the value returned by Context.getFilesDir().

• <cache-path name="name" path="path" />

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  Represents files in the cache subdirectory of your app's internal storage area. The root path of this subdirectory is the same as the value returned by getCacheDir().

• <external-path name="name" path="path" />

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  Represents files in the root of the external storage area. The root path of this subdirectory is the same as the value returned by Environment.getExternalStorageDirectory().

• <external-files-path name="name" path="path"
  />

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  Represents files in the root of your app's external storage area. The root path of this subdirectory is the same as the value returned by Context.getExternalFilesDir(null).

• <external-cache-path name="name" path="path"
  />

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  Represents files in the root of your app's external cache area. The root path of this subdirectory is the same as the value returned by Context.getExternalCacheDir().

• <external-media-path name="name" path="path"
  />

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  Represents files in the root of your app's external media area. The root path of this subdirectory is the same as the value returned by the first result of Context.getExternalMediaDirs().

  Note: this directory is only available on API 21+ devices.

These child elements all use the same attributes:

• name="name"

  A URI path segment. To enforce security, this value hides the name of the subdirectory you're sharing. The subdirectory name for this value is contained in the path attribute.

• path="path"

  The subdirectory you're sharing. While the name attribute is a URI path segment, the path value is an actual subdirectory name. Notice that the value refers to a subdirectory, not an individual file or files. You can't share a single file by its file name, nor can you specify a subset of files using wildcards.

You must specify a child element of <paths> for each directory that contains files for which you want content URIs. For example, these XML elements specify two directories:

<paths xmlns:android="http://schemas.android.com/apk/res/android">
   <files-path name="my_images" path="images/"/>
   <files-path name="my_docs" path="docs/"/>
</paths>

Put the <paths> element and its children in an XML file in your project. For example, you can add them to a new file called res/xml/file_paths.xml. To link this file to the FileProvider, pass it to super() in the constructor for the FileProvider you defined above, add a element as a child of the <provider> element that defines the FileProvider. Set the <meta-data> element's "android:name" attribute to android.support.FILE_PROVIDER_PATHS. Set the element's "android:resource" attribute to @xml/file_paths (notice that you don't specify the .xml extension). For example:

 <provider 
 android:name="com.sample.MyFileProvider" 
 android:authorities="com.mydomain.fileprovider" 
 android:exported="false" 
 android:grantUriPermissions="true"> 
 <meta-data 
 android:name="android.support.FILE_PROVIDER_PATHS" 
 android:resource="@xml/file_paths" /> 
 </provider> 
 

Generating the Content URI for a File

To share a file with another app using a content URI, your app has to generate the content URI. To generate the content URI, create a new File for the file, then pass the File to getUriForFile(). You can send the content URI returned by getUriForFile() to another app in an Intent. The client app that receives the content URI can open the file and access its contents by calling ContentResolver.openFileDescriptor to get a ParcelFileDescriptor.

For example, suppose your app is offering files to other apps with a FileProvider that has the authority com.mydomain.fileprovider. To get a content URI for the file default_image.jpg in the images/ subdirectory of your internal storage add the following code:

 File imagePath = new File(Context.getFilesDir(), "my_images"); 
 File newFile = new File(imagePath, "default_image.jpg"); 
 Uri contentUri = getUriForFile(getContext(), "com.mydomain.fileprovider", newFile); 
 

Granting Temporary Permissions to a URI

To grant an access permission to a content URI returned from getUriForFile(), you can either grant the permission to a specific package or include the permission in an intent, as shown in the following sections.

Call the method Context.grantUriPermission(package, Uri, mode_flags) for the content://Uri, using the desired mode flags. This grants temporary access permission for the content URI to the specified package, according to the value of the the mode_flags parameter, which you can set to FLAG_GRANT_READ_URI_PERMISSION, FLAG_GRANT_WRITE_URI_PERMISSION or both. The permission remains in effect until you revoke it by calling revokeUriPermission() or until the device reboots.

To allow the user to choose which app receives the intent, and the permission to access the content, do the following:

1. Put the content URI in an Intent by calling setData().

2. Call the method Intent.setFlags() with either FLAG_GRANT_READ_URI_PERMISSION or FLAG_GRANT_WRITE_URI_PERMISSION or both.

   To support devices that run a version between Android 4.1 (API level 16) and Android 5.1 (API level 22) inclusive, create a ClipData object from the content URI, and set the access permissions on the ClipData object:

    shareContentIntent.setClipData(ClipData.newRawUri("", contentUri)); 
    shareContentIntent.addFlags( 
    Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION); 
    

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3. Send the Intent to another app. Most often, you do this by calling setResult().

Permissions granted in an Intent remain in effect while the stack of the receiving Activity is active. When the stack finishes, the permissions are automatically removed. Permissions granted to one Activity in a client app are automatically extended to other components of that app.

Serving a Content URI to Another App

There are a variety of ways to serve the content URI for a file to a client app. One common way is for the client app to start your app by calling startActivityResult(), which sends an Intent to your app to start an Activity in your app. In response, your app can immediately return a content URI to the client app or present a user interface that allows the user to pick a file. In the latter case, once the user picks the file your app can return its content URI. In both cases, your app returns the content URI in an Intent sent via setResult().

You can also put the content URI in a ClipData object and then add the object to an Intent you send to a client app. To do this, call Intent.setClipData(). When you use this approach, you can add multiple ClipData objects to the Intent, each with its own content URI. When you call Intent.setFlags() on the Intent to set temporary access permissions, the same permissions are applied to all of the content URIs.

Note: The Intent.setClipData() method is only available in platform version 16 (Android 4.1) and later. If you want to maintain compatibility with previous versions, you should send one content URI at a time in the Intent. Set the action to ACTION_SEND and put the URI in data by calling setData().

To learn more about FileProvider, see the Android training class Sharing Files Securely with URIs.