How to solve scrolling in list view when gridview as a child?

Instead of use ListView you should use Column Widget Like below.

    body: 
        Column(
      children: <Widget>[
        Container (
         height: 150.0, // Set as you want
        child: Image.network("https://www.gizbot.com/img/2013/11/23-weekend-deals-top-10-latest-smartphones.jpg")),
        Container(
        height: 300.0,
        child: GridView.count(
          crossAxisCount: 3,
          childAspectRatio: .6,
          children: _list.map((p) => ProductManagment(p)).toList(),
        ),
      ) 
      ],
    )

Because of `GridView` itself has scroll effect.

EDITED:

Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Container(
          child: ListView(
            children: <Widget>[
              Column(
                children: <Widget>[
                  Container(
                    height: 200,
                    child: Image.network(
                        "https://www.gizbot.com/img/2013/11/23-weekend-deals-top-10-latest-smartphones.jpg"),
                  ),
                  ConstrainedBox(
                    constraints: BoxConstraints(
                      minHeight: 80, // Set as you want or you can remove it also.
                      maxHeight: double.infinity,
                    ),
                    child: Container(
                      child: GridView.count(
                        crossAxisCount: 3,
                        shrinkWrap: true,
                        scrollDirection: Axis.vertical,
                        physics: NeverScrollableScrollPhysics(),
                        childAspectRatio: .6,
                        children: _list.map((p) => ProductManagment(p)).toList(),
                      ),
                    ),
                  )
                ],
              ),
            ],
          ),
        ));

You have to use ConstrainedBox with set maxHeight: double.infinity and GridView.count set shrinkWrap: true,. and remove container height 300.

Also if you want to change

 Container(
                    height: 200,
                    child: Image.network(
                        "https://www.gizbot.com/img/2013/11/23-weekend-deals-top-10-latest-smartphones.jpg"),
                  ),

To Just

 Image.network("https://www.gizbot.com/img/2013/11/23-weekend-deals-top-10-latest-smartphones.jpg")

Than you can change it.