spinnerRect method
获取当前筛选框头部的坐标信息
Implementation
Rect spinnerRect() {
final render = targetKey.currentContext!.findRenderObject() as RenderBox;
final topLeft = render.localToGlobal(Offset.zero);
return Rect.fromPoints(
topLeft,
Offset(
topLeft.dx + render.size.width,
topLeft.dy + render.size.height,
),
);
}