如果不固定父容器的高度，则GridView.Count不可见

因为你用SingleChildScrollView作为您的父部件GridView，所以您需要指定primary: false和shrinkWrap: true因此，GridView根据项目计数取最小的高度。

完整代码：

void main() {
  runApp(new MaterialApp(
    home: new MyHome(),
 ));
}

class MyHome extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

TextEditingController controller = new TextEditingController();

class _AppState extends State<MyHome> {
  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: PreferredSize(
        preferredSize: Size(null, 180),
        child: CustomAppBar(_scaffoldKey, controller),
      ),
      drawer: createDrawer(),
      body: SingleChildScrollView(
        child: Container(
          color: Colors.black12,
      //=========Main Container For Scrollview==============//
          child: Padding(
            padding: const EdgeInsets.fromLTRB(0, 15, 0, 0),
            child: Column(
              children: <Widget>[
                Container(
              //================Container for Categories==================//
                  color: Colors.white,
                  child: Padding(
                    padding: const EdgeInsets.fromLTRB(15, 10, 15, 10),
                    child: Row(
                      mainAxisAlignment: MainAxisAlignment.spaceBetween,
                      children: <Widget>[
                        Column(
                          children: <Widget>[
                        CircleAvatar(
                          backgroundImage:
                              ExactAssetImage('images/user_icon.png'),
                          minRadius: 20,
                          maxRadius: 30,
                        ),
                        Text(
                          'Women',
                          style: TextStyle(
                              fontSize: 13,
                              color: Colors.black,
                              fontFamily: 'SFProRegular'),
                        )
                      ],
                    ),
                    Column(
                      children: <Widget>[
                        CircleAvatar(
                          backgroundImage:
                              ExactAssetImage('images/user_icon.png'),
                          minRadius: 20,
                          maxRadius: 30,
                        ),
                        Text(
                          'Women',
                          style: TextStyle(
                              fontSize: 13,
                              color: Colors.black,
                              fontFamily: 'SFProRegular'),
                        )
                      ],
                    ),
                    Column(
                      children: <Widget>[
                        CircleAvatar(
                          backgroundImage:
                              ExactAssetImage('images/user_icon.png'),
                          minRadius: 20,
                          maxRadius: 30,
                        ),
                        Text(
                          'Women',
                          style: TextStyle(
                              fontSize: 13,
                              color: Colors.black,
                              fontFamily: 'SFProRegular'),
                        )
                      ],
                    ),
                    Column(
                      children: <Widget>[
                        CircleAvatar(
                          backgroundImage:
                              ExactAssetImage('images/user_icon.png'),
                          minRadius: 20,
                          maxRadius: 30,
                        ),
                        Text(
                          'Women',
                          style: TextStyle(
                              fontSize: 13,
                              color: Colors.black,
                              fontFamily: 'SFProRegular'),
                        )
                      ],
                    ),
                  ],
                ),
              ),
            ),
            Card(
              child: SizedBox(
                  height: 200.0,
                  child: Carousel(
                    images: [
                      NetworkImage(
                          'https://cdn-images-1.medium.com/max/2000/1*GqdzzfB_BHorv7V2NV7Jgg.jpeg'),
                      NetworkImage(
                          'https://cdn-images-1.medium.com/max/2000/1*wnIEgP1gNMrK5gZU7QS0-A.jpeg'),
                    ],
                    dotSize: 4.0,
                    dotSpacing: 15.0,
                    indicatorBgPadding: 5.0,
                    borderRadius: false,
                  )),
            ),
 GridView.count(   
shrinkWrap: true,
primary: false,  
              childAspectRatio: 4.0,
              // Create a grid with 2 columns. If you change the scrollDirection to
              // horizontal, this produces 2 rows.
              crossAxisCount: 2,
              // Generate 100 widgets that display their index in the List.
              children: List.generate(100, (index) {
                return Center(
                  child: Text(
                    'Item $index',
                    style: Theme.of(context).textTheme.headline,
                  ),
                );
              }),
            )
          ],
        ),
      ),
    ),
    ),
    );
  }
}