attach method

@override void attach(PipelineOwner owner)

Mark this render object as attached to the given owner.

Typically called only from the parent's attach method, and by the owner to mark the root of a tree as attached.

Subclasses with children should override this method to attach all their children to the same owner after calling the inherited method, as in super.attach(owner).

Implementation

@override
void attach(PipelineOwner owner) {
  super.attach(owner);
  _leftDrag = HorizontalDragGestureRecognizer(debugOwner: this)
    ..onStart = (DragStartDetails details) {
      _isDraggingLeft = true;

      // Calculate where the mouse is relative to the exact visual line of the divider.
      // This prevents the divider from instantly jumping to the mouse center if the user
      // grabbed the slop edge. By subtracting physical X from mouse X, we get the offset.
      final Offset localPos = globalToLocal(details.globalPosition);
      _leftDragGrabOffset = localPos.dx - _leftDividerX;

      markNeedsPaint();
    }
    ..onUpdate = (DragUpdateDetails details) {
      if (!hasSize) {
        return;
      }

      final Offset localPos = globalToLocal(details.globalPosition);

      // Target where the divider *should* go by removing the initial grab offset.
      final double desiredLeftWidth = localPos.dx - _leftDragGrabOffset;

      final double currentRightWidth = childForSlot(DesktopPaneSlot.right)?.size.width ?? 0.0;
      final double maxLeft = size.width - _minContentWidth - currentRightWidth;

      leftPaneWidth = math.min(maxLeft, desiredLeftWidth);
    }
    ..onEnd = (_) {
      _isDraggingLeft = false;
      markNeedsPaint();
    }
    ..onCancel = () {
      _isDraggingLeft = false;
      markNeedsPaint();
    };

  _rightDrag = HorizontalDragGestureRecognizer(debugOwner: this)
    ..onStart = (DragStartDetails details) {
      _isDraggingRight = true;

      final Offset localPos = globalToLocal(details.globalPosition);
      _rightDragGrabOffset = localPos.dx - _rightDividerX;

      markNeedsPaint();
    }
    ..onUpdate = (DragUpdateDetails details) {
      if (!hasSize) {
        return;
      }

      final Offset localPos = globalToLocal(details.globalPosition);

      // 1. Calculate where the right divider *should* go.
      final double desiredDividerX = localPos.dx - _rightDragGrabOffset;

      // 2. Map that absolute X coordinate backward into the width of the right pane.
      final double desiredRightWidth = size.width - desiredDividerX;

      final double currentLeftWidth = childForSlot(DesktopPaneSlot.left)?.size.width ?? 0.0;
      final double maxRight = size.width - _minContentWidth - currentLeftWidth;

      rightPaneWidth = math.min(maxRight, desiredRightWidth);
    }
    ..onEnd = (_) {
      _isDraggingRight = false;
      markNeedsPaint();
    }
    ..onCancel = () {
      _isDraggingRight = false;
      markNeedsPaint();
    };
}