build method

  1. @override
Widget build(
  1. BuildContext context
)
override

Describes the part of the user interface represented by this widget.

The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes). This method can potentially be called in every frame and should not have any side effects beyond building a widget.

The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.

Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor and from the given BuildContext.

The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. A given widget might be built with multiple different BuildContext arguments over time if the widget is moved around the tree or if the widget is inserted into the tree in multiple places at once.

The implementation of this method must only depend on:

If a widget's build method is to depend on anything else, use a StatefulWidget instead.

See also:

  • StatelessWidget, which contains the discussion on performance considerations.

Implementation

@override
Widget build(BuildContext context) {
  // Use controller's theme as single source of truth
  final theme = controller.theme ?? NodeFlowTheme.light;
  final nodeTheme = theme.nodeTheme;

  return Observer(
    builder: (context) {
      // Check visibility first - return nothing if hidden
      if (!node.isVisible) {
        return const SizedBox.shrink();
      }

      // Use visual position for rendering
      final position = node.visualPosition.value;
      final isSelected = node.isSelected;
      final size = node.size.value;

      // Derive cursor from interaction state based on layer
      final cursor = theme.cursorTheme.cursorFor(
        _isAnnotationLayer ? ElementType.annotation : ElementType.node,
        controller.interaction,
        isLocked: node.locked,
      );

      // Determine if resize handles should be shown
      final showResizeHandles = isSelected && node.isResizable;

      return Positioned(
        left: position.dx,
        top: position.dy,
        child: UnboundedSizedBox(
          width: size.width,
          height: size.height,
          child: UnboundedStack(
            clipBehavior: Clip.none, // Allow ports/handles to overflow
            children: [
              // Main node visual with gesture handling via ElementScope
              Positioned.fill(
                child: ElementScope(
                  // Session for canvas locking during drag
                  createSession: () =>
                      controller.createSession(DragSessionType.nodeDrag),
                  // Drag lifecycle - unified for all node types (including GroupNode, CommentNode)
                  isDraggable: !node.locked,
                  onDragStart: (_) => controller.startNodeDrag(node.id),
                  onDragUpdate: (details) =>
                      controller.moveNodeDrag(details.delta),
                  onDragEnd: (_) => controller.endNodeDrag(),
                  // Interaction callbacks
                  onTap: onTap,
                  onDoubleTap: onDoubleTap,
                  onContextMenu: onContextMenu,
                  onMouseEnter: onMouseEnter,
                  onMouseLeave: onMouseLeave,
                  cursor: cursor,
                  // Background/foreground layers use translucent for hit testing to allow clicks through transparent areas
                  hitTestBehavior: _isAnnotationLayer
                      ? HitTestBehavior.translucent
                      : HitTestBehavior.opaque,
                  // Autopan configuration
                  autoPan: controller.config.autoPan.value,
                  getViewportBounds: () =>
                      controller.viewportScreenBounds.rect,
                  onAutoPan: (delta) {
                    // Pan viewport (convert graph units to screen units)
                    final zoom = controller.viewport.zoom;
                    controller.panBy(
                      ScreenOffset(
                        Offset(-delta.dx * zoom, -delta.dy * zoom),
                      ),
                    );
                  },
                  // Node visual - check for self-rendering first
                  child: _buildNodeVisual(context, nodeTheme, isSelected),
                ),
              ),

              // Input ports (positioned on edges - only for middle layer nodes)
              if (!_isAnnotationLayer)
                ...node.inputPorts.map(
                  (port) => _buildPort(context, port, false, nodeTheme),
                ),

              // Output ports (positioned on edges - only for middle layer nodes)
              if (!_isAnnotationLayer)
                ...node.outputPorts.map(
                  (port) => _buildPort(context, port, true, nodeTheme),
                ),

              // Resize handles (only when selected and resizable)
              if (showResizeHandles)
                Positioned.fill(
                  child: ResizerWidget(
                    handleSize: theme.resizerTheme.handleSize,
                    color: theme.resizerTheme.color,
                    borderColor: theme.resizerTheme.borderColor,
                    borderWidth: theme.resizerTheme.borderWidth,
                    snapDistance: theme.resizerTheme.snapDistance,
                    onResizeStart: (handle) =>
                        controller.startResize(node.id, handle),
                    onResizeUpdate: (delta) => controller.updateResize(delta),
                    onResizeEnd: () => controller.endResize(),
                    child: const SizedBox.expand(),
                  ),
                ),
            ],
          ),
        ),
      );
    },
  );
}