Why using a FileProvider I can’t open file from INTERNAL STORAGE with external apps?

Understanding FileProvider and Internal Storage

Android’s security model restricts access to an app’s internal storage to only that specific app. FileProvider, introduced in Android N (7.0), provides a mechanism to securely share files within an app or with external apps.

The Conflict: FileProvider and Internal Storage

How FileProvider Works

FileProvider generates a content URI, a special type of URI used to access files within an app. This URI acts as a temporary access token, allowing other apps to view or interact with the specified file.

Why Internal Storage Access is Restricted

Android’s security model prioritizes app isolation. Direct access to internal storage from external apps poses security risks:

• Data Theft: Malicious apps could potentially access sensitive user data stored within your app’s internal storage.
• App Tampering: External apps could modify or delete your app’s data, potentially causing malfunctions.

Why You Can’t Directly Open Files

FileProvider itself doesn’t prevent you from opening files from internal storage; it’s the security model that restricts access. Here’s how the conflict arises:

• FileProvider URI: When you share a file with FileProvider, the URI returned is designed for temporary, controlled access.
• External App’s Intent: When an external app tries to open the file using the URI, it’s asking Android for direct access to the file on your internal storage.
• Security Check: Android checks if the external app has permission to access that file. Since it’s your app’s internal storage, the external app doesn’t have permission.

Solutions

1. Exporting Files

The most straightforward solution is to move the file from internal storage to a location accessible by other apps (e.g., external storage).

2. Using a Content Provider

For more structured access control, consider implementing a Content Provider. Content Providers allow you to define rules for accessing your data, ensuring controlled access even when shared with other apps.

Example: Sharing a File with FileProvider

<!-- ... Inside your AndroidManifest.xml ... -->
<application ... >
  <provider
      android:name=".FileProvider"
      android:authorities=".your.package.name.fileprovider"
      android:exported="false"
      android:grantUriPermissions="true">
      <meta-data
          android:name="android.support.FILE_PROVIDER_PATHS"
          android:resource="@xml/file_paths"/>
  </provider>
</application>

<!-- ... Inside your res/xml/file_paths.xml ... -->
<?xml version="1.0" encoding="utf-8"?>
<paths>
  <external-path name="external_files" path="."/>
  <files-path name="internal_files" path="files"/>
</paths>

// ... Inside your activity's code ...
File file = new File(getFilesDir(), "my_file.txt");
Uri uri = FileProvider.getUriForFile(this, "your.package.name.fileprovider", file);

Intent shareIntent = new Intent(Intent.ACTION_SEND);
shareIntent.setType("text/plain");
shareIntent.putExtra(Intent.EXTRA_STREAM, uri);
shareIntent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);

startActivity(Intent.createChooser(shareIntent, "Share File"));

Summary

While FileProvider facilitates secure file sharing within Android, direct access to your app’s internal storage from external apps is restricted due to security concerns. To enable this functionality, consider exporting files or implementing a Content Provider to provide controlled access to your data.