Key points:

• Create a TextEditingController widget for each TextField that the user will see.
• Use the same UI both for insert and update. The isnew Boolean value will help decide which task to perform.
• It's always a good idea to place widgets in scrolling widgets. Here, we use the SingleChildScrollView widget.

Solution:

Create the ListItemDialog class in the list_item_dialog.dart file, as follows:

import 'package:flutter/material.dart';
import '../models/list_items.dart';
import '../util/dbhelper.dart';

class ListItemDialog  {
  final txtName = TextEditingController();
  final txtQuantity = TextEditingController();
  final txtNote = TextEditingController();
  Widget buildAlert(BuildContext context, ListItem item, bool isNew) {
    DbHelper helper = DbHelper();
    helper.openDb();
    if (!isNew) {
      txtName.text = item.name;
      txtQuantity.text = item.quantity;
      txtNote.text = item.note;
    }
    return AlertDialog(
      title: Text((isNew)?'New shopping item':'Edit shopping item'),
      content: SingleChildScrollView(
        child: Column(children: <Widget>[
          TextField(
            controller: txtName,
            decoration: InputDecoration(
              hintText: 'Item Name'
            ) 
          ),
          TextField(
            controller: txtQuantity,
            decoration: InputDecoration(
              hintText: 'Quantity'
            ) ,
          ),
          TextField(
            controller: txtNote,
            decoration: InputDecoration(
              hintText: 'Note'
            ) ,
          ),
          RaisedButton(
            child: Text('Save Item'),
            onPressed: (){
                item.name = txtName.text;
                item.quantity = txtQuantity.text;
                item.note = txtNote.text;
                helper.insertItem(item);
                Navigator.pop(context);
            },
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(30.0)
            )  )   ],),      ),    );  }}

Now that the ListItemDialog is complete, let's add it to the ItemsScreen.