A Flutter long press context menu. Wrap a child with LongPressPopupMenu and it pops up at press location with its PopupMenuItem:s

main.dart

// BSD 3-Clause License
//
// Copyright (c) 2021, Mike Rydstrom (Rydmike)
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
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// 3. Neither the name of the copyright holder nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// POSSIBILITY OF SUCH DAMAGE.
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

/// This is the main application widget.
class MyApp extends StatelessWidget {
  /// Default const constructor.
  const MyApp({Key? key}) : super(key: key);

  /// title for the application, also used in home screen's app bar
  static const String title = 'Long Press Menu';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: title,
      home: const HomeScreen(title: title),
      theme: ThemeData.from(colorScheme: const ColorScheme.light()),
      darkTheme: ThemeData.from(colorScheme: const ColorScheme.dark()),
      themeMode: ThemeMode.light,
    );
  }
}

/// The home screen of this simple demo app.
class HomeScreen extends StatelessWidget {
  /// Default const constructor.
  const HomeScreen({Key? key, required this.title}) : super(key: key);

  /// AppBar title of the home screen.
  final String title;

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    return Scaffold(
      appBar: AppBar(title: Text(title)),
      body: Theme(
        // Just an example of how to theme the popup menu and its icons a bit
        // to make the long press context menu a bit prettier.
        data: theme.copyWith(
          popupMenuTheme: PopupMenuThemeData(
            color: theme.cardColor.withOpacity(0.9),
            elevation: 3,
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(8),
            ),
          ),
          iconTheme: const IconThemeData(size: 16),
        ),
        child: Center(
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              const Spacer(),
              Expanded(
                flex: 4,
                child: Container(
                  height: 200,
                  color: theme.colorScheme.primary,
                  child: Center(
                      child: Text(
                    'No action here',
                    style: theme.primaryTextTheme.headline6,
                    textAlign: TextAlign.center,
                  )),
                ),
              ),
              const SizedBox(width: 8),
              Expanded(
                flex: 4,
                child: CutCopyPasteMenu(
                  child: Container(
                    color: theme.colorScheme.secondary,
                    height: 200,
                    child: Center(
                      child: Text(
                        'Long press me',
                        style: theme.accentTextTheme.headline6,
                        textAlign: TextAlign.center,
                      ),
                    ),
                  ),
                ),
              ),
              const Spacer(),
            ],
          ),
        ),
      ),
    );
  }
}

/// A cut, copy paste menu example.
@immutable
class CutCopyPasteMenu extends StatelessWidget {
  /// Default const constructor.
  const CutCopyPasteMenu({Key? key, required this.child}) : super(key: key);

  /// The child that gets the CutCopyPaste long press menu.
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return LongPressPopupMenu<String>(
      items: <PopupMenuEntry<String>>[
        PopupMenuItem<String>(
          value: 'cut',
          height: 30,
          child: SizedBox(
            width: 80,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: const <Widget>[
                Text('Cut'),
                Icon(Icons.cut),
                // Text('⌘ X'), // The ⌘ char did not work in DartPad.
              ],
            ),
          ),
        ),
        PopupMenuItem<String>(
          value: 'copy',
          height: 30,
          child: SizedBox(
            width: 80,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: const <Widget>[
                Text('Copy'),
                Icon(Icons.copy),
                // Text('⌘ C'), // The ⌘ char did not work in DartPad.
              ],
            ),
          ),
        ),
        PopupMenuItem<String>(
          value: 'paste',
          height: 30,
          child: SizedBox(
            width: 80,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: const <Widget>[
                Text('Paste'),
                Icon(Icons.paste),
                // Text('⌘ V'), // The ⌘ char did not work in DartPad.
              ],
            ),
          ),
        ),
      ],
      onSelected: (String? value) async {
        if (value != null) {
          // Just wait 400ms so we can see the menu animate close after
          // selection before we show a snack bar.
          await Future<void>.delayed(const Duration(milliseconds: 400));
          // Show a snack bar with the selected item.
          ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(
              content: Text('Long press menu selection ${value.toUpperCase()}'),
              duration: const Duration(milliseconds: 1800),
            ),
          );
        }
      },
      child: child,
    );
  }
}

/// A simple long press popup menu.
@immutable
class LongPressPopupMenu<T> extends StatefulWidget {
  /// The popup menu entries for the long press menu.
  final List<PopupMenuEntry<T>> items;

  /// ValueChanged callback with selected item in the long press menu.
  /// Is null if menu closed without selection by clicking outside the menu.
  final ValueChanged<T?> onSelected;

  /// The child that can be long pressed to activate the long press menu.
  final Widget child;

  /// Default constructor
  const LongPressPopupMenu({
    Key? key,
    required this.child,
    required this.items,
    required this.onSelected,
  }) : super(key: key);

  @override
  State<StatefulWidget> createState() => _LongPressPopupMenuState<T>();
}

class _LongPressPopupMenuState<T> extends State<LongPressPopupMenu<T>> {
  Offset _downPosition = const Offset(0, 0);

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
        behavior: HitTestBehavior.translucent,
        onTapDown: (TapDownDetails details) {
          _downPosition = details.globalPosition;
        },
        onLongPress: () async {
          final RenderBox? overlay =
              Overlay.of(context)?.context.findRenderObject() as RenderBox?;
          if (overlay != null) {
            final T? value = await showMenu<T>(
              context: context,
              items: widget.items,
              position: RelativeRect.fromLTRB(
                _downPosition.dx,
                _downPosition.dy,
                overlay.size.width - _downPosition.dx,
                overlay.size.height - _downPosition.dy,
              ),
            );
            widget.onSelected(value);
          }
        },
        child: widget.child);
  }
}

NOTE: This Gist requires Dart SDK >=2.12.0-0 with sound null safety!

Set Dart SDK environment to:

environment:
  sdk: '>=2.12.0-0 <3.0.0'

in your pubspec.yaml.