Support Native Media Gallery Indexing / scanFile API on Android (Serious Python)

[fazi-gondal]

Context

When building multi-platform Python applications with Flet and compiling them for Android using Serious Python, apps often need to download or save media files (videos, photos, audio) to public user directories (such as the standard Download/ folder).

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The Problem

When a file is downloaded or created directly on the filesystem under public storage (e.g., /storage/emulated/0/Download/), other Android apps (like WhatsApp, Instagram, TikTok) and the native system Gallery do not show the new file automatically.

The files are technically present on disk, but they remain invisible to other apps until the user manually opens the Android system File Manager. Opening the File Manager forces a system-level ContentObserver folder scan, which finally registers the files in the Android MediaStore database.

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What We Tried (And the JNI / PyJNIus Traps)

We attempted to solve this within Python code using PyJNIus (jnius) to manually trigger the Android MediaScannerConnection.scanFile() API. However, doing this from Python runs into several major JNI and Serious Python structural blocks:

1. PyJNIus Background Thread Attachment Trap

Flet events and background tasks run on Python background worker threads (like asyncio or threading loops). PyJNIus calling Java methods from a background thread fails silently or crashes unless jnius.attach_thread() is explicitly called beforehand.

import jnius
jnius.attach_thread()  # Required, but undocumented and highly prone to runtime errors

2. Changing Host Activity Class Names

To initialize MediaScannerConnection, we need the application Context. In Serious Python, finding the host activity via class lookups is brittle because class names vary between Serious Python versions:

• Older: com.flet.serious_python_android.PythonActivity
• Newer: com.flet.serious_python.PythonActivity
• Fallback lookups like android.app.ActivityThread.currentApplication() frequently return null when called from Python worker threads.

3. JNI Signature Matching Failures

PyJNIus has trouble converting Python list structures to Java String[] array signatures expected by scanFile(Context, String[], String[], OnScanCompletedListener). Developers have to construct Java arrays manually via JNI reflection:

Array = autoclass('java.lang.reflect.Array')
String = autoclass('java.lang.String')
paths_arr = Array.newInstance(String, len(file_paths)) # Brittle reflection setup

4. Android 9+ Implicit Intent Blocks

Fallback intent broadcasts like android.intent.action.MEDIA_SCANNER_SCAN_FILE are ignored on Android 9+ unless explicitly targeted to the Media Provider package (-p com.android.providers.media), making shell-based workarounds highly complex and security-restricted.

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Proposed Solution (Feature Request)

To make Flet a truly first-class framework for mobile development, Flet should expose a native, cross-platform media indexing API (for example, page.scan_media(path) or a new page.storage_paths.scan_file(path) service method).

How it should work under the hood:

1. The Flet Flutter client should handle the media scanner connection natively on the Dart side.
2. In Dart, triggering a media scan on Android is extremely simple and does not suffer from classloader or background-thread JNI issues:

   // Dart side handler
   import 'package:flutter/services.dart';
   // Native MethodChannel triggers MediaScannerConnection.scanFile on the Android Activity thread

3. By delegating this to the Flutter shell, Python developers wouldn't need to write brittle PyJNIus wrappers, deal with JNI JVM thread-attachments, or worry about changing package class names between Serious Python releases.

This feature is essential for any Flet application that downloads user-facing files (photos, videos, PDF documents, audio) to public directories on Android.