How to use Flutter to build a bottom sheet widget which is able to drag up to full screen?

Use the DraggableBottomSheet widget with the Stack widget:

Here's the gist for the entire page in this^ GIF, or try the Codepen.

Here's the structure of the entire page:

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          CustomGoogleMap(),
          CustomHeader(),
          DraggableScrollableSheet(
            initialChildSize: 0.30,
            minChildSize: 0.15,
            builder: (BuildContext context, ScrollController scrollController) {
              return SingleChildScrollView(
                controller: scrollController,
                child: CustomScrollViewContent(),
              );
            },
          ),
        ],
      ),
    );
  }

In the Stack:
- The Google map is the lower most layer.
- The Header (search field + horizontally scrolling chips) is above the map.
- The DraggableBottomSheet is above the Header.

Some useful parameters as defined in draggable_scrollable_sheet.dart:

  /// The initial fractional value of the parent container's height to use when
  /// displaying the widget.
  ///
  /// The default value is `0.5`.
  final double initialChildSize;

  /// The minimum fractional value of the parent container's height to use when
  /// displaying the widget.
  ///
  /// The default value is `0.25`.
  final double minChildSize;

  /// The maximum fractional value of the parent container's height to use when
  /// displaying the widget.
  ///
  /// The default value is `1.0`.
  final double maxChildSize;

Neither the modal nor the persistent bottomsheets can be dragged into view. The persistent bottomsheet must be triggered open (e.g., by pressing a button) & THEN it may be dragged up & down until finally out of view. I wish there was an option to allow it to be dragged into view...

Rubber should meet your needs; I gave it a try but it always freaks out when I call setstate (so a no go for me)... Let me know if you have the same problems.