Handling android file intent in app

[nikhild1836]

Question

Hello,
I started building android apps with Flet about three months ago, so a newbie. I would like my app to access/display the contents of a text file when a text file is selected in the file manager and directed to my app. I understand this is called handling the "android intent". I have spent quite some time on google to try to find a solution to this problem and have not got a clear answer if this doable in pure python or not. Is there an example where this has been implemented which I can use as a starting point?

      I don't mind if the solution requires using pyjnius or a bit of kotlin. (I am not very familiar with pyjnius/kotlin but many LLM solutions point towards these being needed)

     I see an issue related to this: https://github.com/flet-dev/flet/issues/6671 But there are no responses yet. 

Thank you,
Nik.
PS: I would like to add that I am enjoying building android apps using the Flet project a lot. Appreciate the work that the developers have put in to make this possible.

Code sample

No response

Error message

No response

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• I have searched for answers to my question both in the issues and in previous discussions.

[RenSolvyn]

Hi Nik, good news: this is more achievable than the older threads suggest, and pyjnius is supported in Flet, contrary to what a lot of search results will tell you.

There are two halves to this, and they are solved in different ways.

1. Declaring the intent filter (build time)

Android decides which apps appear in the "Open with" list by reading <intent-filter> declarations from AndroidManifest.xml at install time, before any of your code runs. That means no runtime API in any language can register it. It has to happen at build time.

Flet handles this through pyproject.toml. The Packaging app for Android docs cover adding or overriding attributes in the generated AndroidManifest.xml. That is where your filter goes, something along these lines:

<intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <data android:mimeType="text/plain" />
</intent-filter>
<intent-filter>
    <action android:name="android.intent.action.SEND" />
    <category android:name="android.intent.category.DEFAULT" />
    <data android:mimeType="text/plain" />
</intent-filter>

2. Reading the incoming intent (runtime)

This is where pyjnius comes in, and it does work in Flet. See the official post: Tap into native Android and iOS APIs with Pyjnius and Pyobjus. Add pyjnius as an Android-only dependency in pyproject.toml, then reach the current Activity and pull the intent off it:

from jnius import autoclass, cast

def read_incoming_file():
    PythonActivity = autoclass("org.kivy.android.PythonActivity")
    activity = cast("android.app.Activity", PythonActivity.mActivity)
    intent = activity.getIntent()
    uri = intent.getData()
    if uri is None:
        return None
    stream = activity.getContentResolver().openInputStream(uri)
    # read the stream into bytes, then decode as text

Three things that will bite you

In rough order of likelihood:

Use ContentResolver, not a file path. You will receive a content:// URI, and under scoped storage the raw filesystem path is usually not readable. openInputStream(uri) is the reliable route.

Handle the cold start case. Your app may be launched by the intent rather than already running, so read getIntent() at startup, not only while the app is running. Otherwise it works when the app is already open and silently fails when it is not, which is a confusing bug to track down.

Verify the activity class name. The org.kivy.android.PythonActivity path above comes from the pyjnius / python-for-android convention. Flet's Android host may expose a different activity class. If autoclass cannot find it, that is the first thing to check against Flet's current Android client.

On release builds and R8

If you hit issues that only appear in a release build, that is usually R8 minification renaming classes that autoclass() resolves by name at runtime.

Flet's serious_python_android 4.1.0+ already ships a keep rule for its own activity classes, so that part is handled for you. But any other Java or Kotlin classes bundled in your APK that you resolve by name will need their own keep rules. Android framework classes (android.os.Build, android.content.Intent, and so on) need no rule, since they live in the Android runtime rather than your APK.

Worth testing a release build on a real device before shipping, since this class of problem does not show up in debug.

On issue #6671

Still worth a thumbs up for first class support, since the manifest and intent handling would be much nicer as a proper Flet API. But you should not be blocked in the meantime.

Hope that helps, and good luck with the app.

[nikhild1836]

I am not very familiar with the internals of android or Kotlin, but I got it to work. It involved using both pyjnius and a kotlin file to be put in the flutter_build_template folder.
Also: ActivityThread = autoclass("android.app.ActivityThread") instead of the one from org.kivy

[nikhild1836]

MainActivity.kt.txt
File renamed for uploading. This file needed to be in folder:
flet-build-template\build{{cookiecutter.out_dir}}\android\app\src\main\kotlin{{ cookiecutter.kotlin_dir }}