Flutter how to empty array

Although you clear list by tapping button, list will be added again when 'build' is called.

  @override
  Widget build(BuildContext context) {
    print('browse subcategory');
    print(widget.subCategory);

        widget.subCategory.forEach((subcategory) {
          items['Items'].addAll(subcategory['Items']);
        });

So you need to move initializing list code.

class _BrowserCategoryPage2State extends State<BrowserCategoryPage2> {
  var items = {'Items': []};

  @override
  void initState() {
    super.initState();

    print(widget.subCategory);

    widget.subCategory.forEach((subcategory) {
       items['Items'].addAll(subcategory['Items']);
    });     
    print(items);
    print('sada');
  }

  @override
  Widget build(BuildContext context) {
    print('browse subcategory');
    return Scaffold(
      appBar: buildAppBar(),
      body: Container(
        child: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              buildCategoryHeading(context),
              GridView.builder(
                itemCount: widget.subCategory.length,
                scrollDirection: Axis.vertical,
                shrinkWrap: true,
                physics: ScrollPhysics(),
                padding: EdgeInsets.symmetric(horizontal: 18.0),
                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                  crossAxisCount: 4,
                  crossAxisSpacing: 15.0,
                  mainAxisSpacing: 15.0,
                  childAspectRatio: 4.0 / 7.0,
                ),
                itemBuilder: (context, index) {
                  var category = categoryList[index];
                  double duration = index / 2;
                  return FadeInAnimation(
                    duration.toInt(),
                    child: GestureDetector(
                        onTap: (){
                          print(widget.subCategory[index]['Items']);
                          setState(() {
                            items = {'Items': []};
                            // Or 
                            // items['Items'].clear();
                            print(items);
                          });


                        },
                        child: Container(
                          width: 80.0,
                          child: Column(
                            children: <Widget>[
                              Container(
                                width: 60.0,
                                height: 60.0,
                                decoration: BoxDecoration(
                                  shape: BoxShape.circle,
                                  border: Border.all(
                                      color: Theme.of(context)
                                          .accentColor
                                          .withOpacity(.2)),
                                  image: DecorationImage(
                                    image: AssetImage(
                                        'assets/icons/shirt.png'),
                                  ),
                                ),
                              ),
                              SizedBox(height: 12.0),
                              Text(
                                widget.subCategory[index]['Name'],
                                textAlign: TextAlign.center,
                                maxLines: 2,
                                overflow: TextOverflow.ellipsis,
                                style: Theme.of(context)
                                    .textTheme
                                    .subtitle2,
                              ).tr(),
                            ],
                          ),
                        )
                    ),
                  );
                },
              ),
              
            ],
          ),
        ),
      ),
    );
  }
}