How to open (audio) file from file manager using Flutter app

You need using ChannelPlatform to do that:

1. Android side:

   Handle onCreate + onNewIntent to get bundle data from File Viewer App that share audio file's path

2. Flutter side:

  get audio file's path and do something...

Demo:

Example:

Android

import android.content.Intent
import android.os.Bundle
import androidx.annotation.NonNull
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugins.GeneratedPluginRegistrant

class MainActivity : FlutterActivity() {
    private val CHANNEL = "tinyappsteam.flutter.dev/open_file"

    var openPath: String? = null
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine)
        val channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL)
        channel.setMethodCallHandler { call, result ->
            when (call.method) {
                "getOpenFileUrl" -> {
                    result.success(openPath)
                }
                else -> result.notImplemented()
            }
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        handleOpenFileUrl(intent)
    }

    override fun onNewIntent(intent: Intent) {
        super.onNewIntent(intent)
        handleOpenFileUrl(intent)
    }

    private fun handleOpenFileUrl(intent: Intent?) {
        val path = intent?.data?.path
        if (path != null) {
            openPath = path
        }
    }
}

Flutter:

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

class _MyHomePageState extends State<MyHomePage> with WidgetsBindingObserver {
  static const platform =
      const MethodChannel('tinyappsteam.flutter.dev/open_file');

  String openFileUrl;

  @override
  void initState() {
    super.initState();
    getOpenFileUrl();
    // Listen to lifecycle events.
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    super.dispose();
    WidgetsBinding.instance.removeObserver(this);
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      getOpenFileUrl();
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Text("Audio file: " + (openFileUrl != null ? openFileUrl : "Nothing!")),
      ),
    );
  }

  void getOpenFileUrl() async {
    dynamic url = await platform.invokeMethod("getOpenFileUrl");
    print("getOpenFileUrl");
    if (url != null && url != openFileUrl) {
      setState(() {
        openFileUrl = url;
      });
    }
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}