Flutter DraggableScrollableSheet not showing up on press of a button

Question

I want to use DraggableScrollableSheet widget on my application, when I use that like with below code, that can show without problem:

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('DraggableScrollableSheet'),
      ),
      body: SizedBox.expand(
        child: DraggableScrollableSheet(
          builder: (BuildContext context, ScrollController scrollController) {
            return Container(
              color: Colors.blue[100],
              child: ListView.builder(
                controller: scrollController,
                itemCount: 25,
                itemBuilder: (BuildContext context, int index) {
                  return ListTile(title: Text('Item $index'));
                },
              ),
            );
          },
        ),
      ),
    );
  }
}

but when i want to show that by pressing for example floatingActionButton that don't show

floatingActionButton: GestureDetector(
  child: FloatingActionButton(
    child: Icon(
      Icons.add,
      size: 35.0,
    ),
    elevation: 5,
    backgroundColor: Colors.deepOrange,
    foregroundColor: Colors.white,
    onPressed: (){
      SizedBox.expand(child: DraggableScrollableSheet(
        builder: (BuildContext context, ScrollController scrollController) {
          return Container(
            color: Colors.blue[100],
            child: ListView.builder(
              controller: scrollController,
              itemCount: 25,
              itemBuilder: (BuildContext context, int index) {
                return ListTile(title: Text('Item $index'));
              },
            ),
          );
        },
      ));
    },
  ),
),

Answer 1

If you want to show DraggableScrollableSheet as modal you can use material showModalBottomSheet method to wrap it. Your sheet will be shown as modal, and you do not have to include it in the widget tree. Please note that under the hood it's pushed as new Route to Navigator, with all its consequences.

onPressed: (){
   showModalBottomSheet(
        context: context,
        isScrollControlled: true,
        expand: false,
        backgroundColor: Colors.transparent,
        builder: (context) =>
            DraggableScrollableSheet(
              initialChildSize: 0.64,
              minChildSize: 0.2,
              maxChildSize: 1,
              builder: (context, scrollController) {
                return Container(
                  color: Colors.white,
                  child: ListView.builder(
                    controller: scrollController,
                    itemBuilder: (context, index) {
                        return ListTile(
                          title: Text('Item $index'),
                        );
                      },
                    itemCount: 20,
                  ),
                );
              },
            ),
      );
}

Answer 2

---

If you want to use DraggableScrollableSheet inside showModalBottomSheet, you can simply call this function.

void _showSheet() {
  showModalBottomSheet(
    context: context,
    isScrollControlled: true, // set this to true
    builder: (_) {
      return DraggableScrollableSheet(
        expand: false,
        builder: (_, controller) {
          return Container(
            color: Colors.blue[500],
            child: ListView.builder(
              controller: controller, // set this too
              itemBuilder: (_, i) => ListTile(title: Text('Item $i')),
            ),
          );
        },
      );
    },
  );
}