Flutter Grid view is not scrolling

I had similar code like you a gridview.count() wrapped in singleChildScrollView adding

  physics: ScrollPhysics(),

to GridView.count() Widget Solved my problem

source:https://github.com/flutter/flutter/issues/19205

Add physics: ScrollPhysics() property to Gridview. it iwll scroll.

You have some issues related to the Scroll of your widgets, you can reduce the amount of Widgets using Wrap, like this :

    Container(
            color: Colors.white,
            padding: EdgeInsets.all(10),
            child: SingleChildScrollView(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.stretch,
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  new Text(
                    'Items of products',
                    style: TextStyle(fontWeight: FontWeight.w700, fontSize: 18.0),
                    textAlign: TextAlign.left,
                  ),
                  Padding(
                    padding: const EdgeInsets.only(top: 15.0),
                    child: Wrap(
                      spacing: 20.0,
                      alignment: WrapAlignment.spaceEvenly,
                      children:createCategoryList(),
                ),
                    ],
                ),
                )
            )
            ]
        ),
        );

Add a constraint width or a fixed with to the widget of your item:

    return Container(
          constraints:
                BoxConstraints(maxWidth: MediaQuery.of(context).size.width / 4),
          child: new GestureDetector(