When I developed Learning Card App for Android, I met a problem that the picture I saved didn't appear in the album, I had to find it in the file system, that's very inconvenient., so I tried to fix this. I looked up dart package to find out this function, unfortunately there was no solution. I had to writing custom platform-specific code to refresh album. The following is the specific code.

Step 1: Create the Flutter platform client

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
...
class _MyHomePageState extends State<MyHomePage> {
  static const platform = const MethodChannel('samples.liqiaqia.com/refreshAlbum');

  // Refresh album through platform channel.
  Future<void> _refreshAlbum(String filePath) async {
    try {
      await platform.invokeMethod('refreshAlbum',<String, dynamic>{
        'filePath': filePath,
      });
    } on PlatformException catch (e) {
			//handle error
    }
  }
	
  Future _saveImage() async {
    filePath = '...';
	//Save image...
	//Calling refresh album function
	_refreshAlbum(filePath);
	}
}

Step 2: Add an Android platform-specific implementation using Java

import android.os.Bundle;
import android.content.Intent;
import android.net.Uri;
import java.io.File;

import io.flutter.app.FlutterActivity;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;

public class MainActivity extends FlutterActivity {
    private static final String CHANNEL = "samples.liqiaqia.com/refreshAblum";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        GeneratedPluginRegistrant.registerWith(this);

        new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler(
                new MethodCallHandler() {
                    @Override
                    public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {
                        if (methodCall.method.equals("refreshAlbum")) {
                            refreshAlbum(methodCall.argument("filePath"));
                        }
                    }
                }
        );
    }

    private void refreshAlbum(String filePath) {
        Uri uri = Uri.fromFile(new File(filePath));
        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, uri);
        sendBroadcast(intent);
    }
}

Step 3: rebuild APK

Finally, the picture appears in your album after you saving the picture.