bmiform.dart

var _formKey = GlobalKey<FormState>();
var _formview = Container(
      color: Colors.grey.shade300,
      margin: EdgeInsets.all(8.0),
      padding: EdgeInsets.all(8.0),
      child: SingleChildScrollView(  
        child: Form(
          key: _formKey,
          child: Column(
            children: <Widget>[
              ageFormField(context),
              heightFormField(context),
              weightFormField(),
              Padding(
                padding: EdgeInsets.only(top: 10.0),
                child: calculateButton()
              ,),
            ], 
          ),
        ),
      ),
    );