containerOf method

RenderBox containerOf (BuildContext context)

The RenderBox that defines this decorator's "container". That's the area which is filled if InputDecoration.isFilled is true. It's the area adjacent to InputDecoration.icon and above the widgets that contain InputDecoration.helperText, InputDecoration.errorText, and InputDecoration.counterText.

TextField renders ink splashes within the container.

Implementation 

static RenderBox containerOf(BuildContext context) {
  final _RenderDecoration result = context.ancestorRenderObjectOfType(const TypeMatcher<_RenderDecoration>());
  return result?.container;
}