Android - no_image

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.

Defining a FileProvider

Since the default functionality of FileProvider includes content URI generation for files, you don’t need to define a subclass in code. Instead, you can include a FileProvider in your app by specifying it entirely in XML. To specify the FileProvider component itself, add a <provider> element to your app manifest. Set the android:name attribute to androidx.core.content.FileProvider. Set the android:authorities attribute to a URI authority based on a domain you control; for example, if you control the domain mydomain.com you should use the authority com.mydomain.fileprovider. Set the android:exported attribute to false; the FileProvider does not need to be public. Set the android:grantUriPermissions attribute to true, to allow you to grant temporary access to files. For example:

<manifest>
    ...
    <application>
        ...
        <provider
            android:name="androidx.core.content.FileProvider"
            android:authorities="com.mydomain.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            ...
        </provider>
        ...
    </application>
</manifest>

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" />

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>

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

As a result of the previous snippet, getUriForFile() returns the content URI content://com.mydomain.fileprovider/my_images/default_image.jpg.

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.

Grant Permission to a Specific Package

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 Intent.FLAG_GRANT_READ_URI_PERMISSION, Intent.FLAG_GRANT_WRITE_URI_PERMISSION or both. The permission remains in effect until you revoke it by calling revokeUriPermission() or until the device reboots.

Include the Permission in an Intent

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

• Put the content URI in an Intent by calling setData().
• Call the method Intent.setFlags() with either Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION or both.
• 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.

Links

https://developer.android.com/reference/androidx/core/content/FileProvider

Next Questions

What is ContentProvider?

credit goes to @swayangjit