node_flow 0.2.2

React Flow-style node editor canvas for Flutter: pan/zoom viewport, draggable nodes, drag-to-connect edges, marquee selection, snap guides, and a minimap.

NodeFlow

A React Flow-style node editor canvas for Flutter. Build workflow editors, pipelines, mind maps, and node-based tools with app-defined node widgets on an infinite pan/zoom canvas — with zero dependencies beyond the Flutter SDK.

Features

• Infinite canvas — pan/zoom viewport (InteractiveViewer-backed) with trackpad/mouse disambiguation, fitView, zoomTo, and centerOnNode.
• App-defined nodes — every node is rendered by your nodeBuilder; node payloads are generic (FlowNode<T>), and the canvas auto-measures each node's laid-out size.
• Dragging & selection — single and multi-node drag, locked nodes, grid snap on commit, click/toggle/select-all, and shift-drag marquee selection.
• Alignment snap guides — Figma-style soft snapping against other nodes with dashed guide lines while dragging; the capture radius is a constant screen distance (FlowController.snapGuideThreshold, 8px) at every zoom.
• Ports & connections — input/output ports on any node side, drag-to-connect with compatible-port detection, a live connection preview, and normalized onConnect requests and optional application validation during hover/drop (the canvas never mutates your graph).
• Edges — bezier, smoothstep, or straight routing with React-Flow-compatible path math, optional animated flowing dash, hit-testing, selection, per-edge accent colors, and warning badges on resolvable marked edges.
• Minimap — pannable overview with a viewport indicator.
• Zero-dependency theming — pass a FlowTheme, register one as a ThemeExtension, or use the built-in dark palette.

The canvas is deliberately unopinionated about persistence and history: serialization and undo/redo stay in your app, wired through controller callbacks (onMoveCommitted, onDeleted, onEdgesDeleted).

Getting started

dependencies:
  node_flow: ^0.2.2

Usage

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

class EditorScreen extends StatefulWidget {
  const EditorScreen({super.key});

  @override
  State<EditorScreen> createState() => _EditorScreenState();
}

class _EditorScreenState extends State<EditorScreen> {
  late final FlowController<String, void> controller;

  @override
  void initState() {
    super.initState();
    controller = FlowController<String, void>();
    _setUpGraph();
  }

  void _setUpGraph() {
    controller.addNode(FlowNode(
      id: 'a',
      type: 'card',
      data: 'Hello',
      position: const GraphPosition(Offset(80, 120)),
      ports: const [
        FlowPort(id: 'out', side: PortSide.right, kind: PortKind.output),
      ],
    ));
    controller.addNode(FlowNode(
      id: 'b',
      type: 'card',
      data: 'World',
      position: const GraphPosition(Offset(420, 200)),
      ports: const [
        FlowPort(id: 'in', side: PortSide.left, kind: PortKind.input),
      ],
    ));
    controller.addEdge(FlowEdge(
      id: 'a:out-b:in',
      sourceNodeId: 'a',
      sourcePortId: 'out',
      targetNodeId: 'b',
      targetPortId: 'in',
    ));
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return NodeFlow<String, void>(
      controller: controller,
      nodeBuilder: (context, node) => SizedBox(
        width: 200,
        child: Card(
          child: Padding(
            padding: const EdgeInsets.all(16),
            child: Text(node.data),
          ),
        ),
      ),
      onConnect: (request) {
        controller.addEdge(FlowEdge(
          id: '${request.sourceNodeId}:${request.sourcePortId}-'
              '${request.targetNodeId}:${request.targetPortId}',
          sourceNodeId: request.sourceNodeId,
          sourcePortId: request.sourcePortId,
          targetNodeId: request.targetNodeId,
          targetPortId: request.targetPortId,
        ));
        return true;
      },
    );
  }
}

See example/ for a runnable demo covering static graphs, editing, edge styles, and drag-to-connect.

Connection validation

Pass an optional isValidConnection predicate to reject a proposed edge while it is being dragged. It receives the same output-to-input-normalized request as onConnect. The canvas checks port direction, self-connections, and duplicate port pairs first; invalid targets are not highlighted and never reach onConnect. It checks again at drop time in case application state changed.

NodeFlow<String, void>(
  controller: controller,
  nodeBuilder: (context, node) => Text(node.data),
  isValidConnection: (request) => !controller.edges.any(
    (edge) => edge.targetNodeId == request.targetNodeId &&
        edge.targetPortId == request.targetPortId,
  ),
  onConnect: (request) {
    // Recheck application rules before writing if state can change here.
    if (controller.edges.any((edge) =>
        edge.targetNodeId == request.targetNodeId &&
        edge.targetPortId == request.targetPortId)) return false;
    controller.addEdge(FlowEdge<void>(
      id: '${request.sourceNodeId}:${request.sourcePortId}-'
          '${request.targetNodeId}:${request.targetPortId}',
      sourceNodeId: request.sourceNodeId,
      sourcePortId: request.sourcePortId,
      targetNodeId: request.targetNodeId,
      targetPortId: request.targetPortId,
    ));
    return true;
  },
);

This single-input rule is just an example. Your application decides type, cardinality, and cycle policy. The predicate should be synchronous and must not mutate the graph. Direct controller.addEdge calls are unaffected. The onConnect boolean return is retained for 0.2.x compatibility and does not control whether the canvas adds an edge; your callback owns that operation.

Node data and navigation

Application status belongs in your node data. For example, with a FlowController<JobData, void> whose immutable JobData provides copyWith:

controller.updateNodeData(
  'job-1',
  (data) => data.copyWith(status: JobStatus.running),
);

Render that status with your own badge, progress indicator, or buttons in nodeBuilder. The update rebuilds the node while preserving its position, selection, ports, lock state, and connections. It returns false for an unknown node ID. The updater must return a new value without mutating the controller or previous data. As with replaceNode, the old node's notifiers are disposed; release application-owned resources separately when necessary.

Once the canvas is laid out, navigate to a node without measuring the canvas:

controller.centerOnNode('job-1');

This immediately centers the node at the current zoom. Headless callers can still pass a size: controller.centerOnNode('job-1', const Size(800, 600)). Before a canvas size is known, or if the node is missing, centering does nothing. fitView() fits the whole graph; zoomTo() changes the zoom. Animated navigation is not currently provided. Try Focus Alpha and Toggle Alpha status on the editing demo for a runnable example.

Edge accents

Edges paint in FlowTheme.edge. Give one its own color when the app needs to say something about it — a traversed path, a failing branch, a data type — without borrowing selection, which belongs to the user:

controller.setEdgeAccent('a-b', const Color(0xFF17A398));
controller.clearEdgeAccents(); // back to the theme color

FlowEdge(accent: ...) seeds the color up front instead. Selection still wins: a selected edge paints in FlowTheme.edgeSelected whatever its accent, so the two channels never fight.

Node actions

Use optional onNodeTap, onNodeDoubleTap, and onNodeContextMenu callbacks to open app-owned details, menus, or routes. Primary tap updates selection before calling onNodeTap; when a double-tap callback is present, Flutter delays a single tap while it checks for a second tap. A double tap selects the node once and calls only onNodeDoubleTap. Secondary click and touch long press call onNodeContextMenu with global logical coordinates; they do not change selection. Interactive child widgets retain their own gestures.

NodeFlow<String, void>(
  controller: controller,
  nodeBuilder: (context, node) => Text(node.data),
  onNodeDoubleTap: (node) => showDialog<void>(
    context: context,
    builder: (context) => AlertDialog(title: Text(node.data)),
  ),
);

The editing demo opens a details dialog from double-click and right-click. No built-in panel or router is required.

Theming

Resolution order: explicit widget parameter → ThemeExtension → dark defaults.

// 1. Explicit:
NodeFlow(controller: controller, nodeBuilder: ..., theme: myFlowTheme);

// 2. Via your app ThemeData:
MaterialApp(
  theme: ThemeData(
    extensions: [
      const FlowTheme.dark().copyWith(
        background: Color(0xFF0B1020),
        edge: Colors.tealAccent,
      ),
    ],
  ),
  ...
);

// 3. Nothing — built-in dark palette.

License

MIT