diagram_editor

Flutter library for building interactive diagram editors. Create, connect, and manipulate nodes and links with pan, zoom, and full gesture support.

Quick Start

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

class MyDiagram extends StatelessWidget {
  MyDiagram({super.key});

  final controller = DiagramController<void, void>();

  @override
  Widget build(BuildContext context) {
    return DiagramEditor<void, void>(
      controller: controller,
      componentBuilder: (context, component) => Container(
        color: Colors.blue,
        child: Center(child: Text(component.id)),
      ),
      onCanvasTapUp: (details) {
        controller.addComponent(ComponentData(
          size: const Size(96, 72),
          position: controller.fromCanvasCoordinates(details.localPosition),
        ));
      },
      onComponentTap: (id) => controller.removeComponent(id),
    );
  }
}

Pan, zoom, link joints, and link control all work out of the box.

Type-Safe Custom Data

Use generic type parameters to attach typed data to components and links:

class MyNodeData {
  final Color color;
  final String label;
  MyNodeData({required this.color, required this.label});
}

final controller = DiagramController<MyNodeData, void>(
  componentDataCodec: JsonCodec(
    encode: (d) => {'color': d.color.toHex(), 'label': d.label},
    decode: (j) => MyNodeData(
      color: Color(int.parse(j['color'] as String, radix: 16)),
      label: j['label'] as String,
    ),
  ),
);

// No more casting — data is typed
controller.addComponent(ComponentData(
  data: MyNodeData(color: Colors.blue, label: 'Start'),
  size: const Size(96, 72),
));

// Access data without casting
final node = controller.getComponent('id');
final color = node.data?.color; // Color, not dynamic

Connecting Components

final linkId = controller.connect(
  sourceComponentId: 'node-1',
  targetComponentId: 'node-2',
  linkStyle: LinkStyle(
    arrowType: ArrowType.arrow,
    lineWidth: 2,
    color: Colors.grey,
  ),
);

Configuration

DiagramEditor<MyNodeData, void>(
  controller: controller,
  componentBuilder: (context, data) => MyNodeWidget(data),

  // Canvas config
  canvasConfig: const CanvasConfig(
    backgroundColor: Color(0xFFF5F5F5),
    minScale: 0.2,
    maxScale: 5.0,
  ),

  // Link endpoint alignment strategy
  linkEndpointAlignment: LinkAttachment.oval(),

  // Disable defaults if you want full control
  enableDefaultPanZoom: true,       // default
  enableDefaultLinkControl: true,   // default
  enableDefaultJointControl: true,  // default

  // Links rendered on top of components
  linksOnTop: true,                 // default

  // All gesture callbacks
  onCanvasTapUp: (details) { /* ... */ },
  onComponentTap: (id) { /* ... */ },
  onComponentScaleUpdate: (id, details) { /* ... */ },
  onLinkTap: (id) { /* ... */ },

  // Custom layers
  backgroundBuilder: (context) => [CustomPaint(painter: GridPainter())],
  foregroundBuilder: (context) => [/* selection UI, toolbars, etc. */],
  componentOverlayBuilder: (context, data) => /* resize handles, etc. */,
);

Serialization

// Save
final json = controller.serialize();

// Load
controller.deserialize(json);

Custom data is serialized via the JsonCodec passed to the controller.

API Overview

DiagramController

The central class managing all diagram state.

Category	Methods
Components	addComponent, removeComponent, moveComponent, getComponent, componentExists, components, componentsSorted
Links	connect, removeLink, getLink, linkExists, links
Z-order	bringToFront, sendToBack, setComponentZOrder
Parent-child	setComponentParent, removeComponentParent
Canvas	setCanvasPosition, panCanvas, zoomCanvas, resetCanvasView, fromCanvasCoordinates, toCanvasCoordinates
Joints	insertLinkJoint, removeLinkJoint, showLinkJoints, hideLinkJoints
Serialization	serialize, deserialize

Link Endpoint Alignment

Strategy	Method
Rectangular	LinkAttachment.rectangular() (default)
Oval	LinkAttachment.oval()
Crystal/Diamond	LinkAttachment.crystal()
Center	LinkAttachment.center()

Link Styles

• Arrow types: none, arrow, pointedArrow, circle, centerCircle, semiCircle
• Line types: solid, dashed, dotted

Built-in Painters

• GridPainter — canvas grid background
• ComponentHighlightPainter — selection highlight
• DeleteIconPainter — delete icon overlay

Migration from v0.x

Key changes:

• PolicySet with mixins -> DiagramEditor with callbacks
• canvasWriter.model.addComponent(...) -> controller.addComponent(...)
• componentData.data as MyType -> componentData.data (typed generics)
• provider dependency removed (uses built-in ListenableBuilder)