import 'package:flutter/material.dart';

class ProductCreatePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _ProductCreatePageState();
  }
}

class _ProductCreatePageState extends State<ProductCreatePage> {
  String titleValue;
  String descriptionValue;
  double priceValue;
  //int是整數，double可以有小數

  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.all(10.0),
      //外層加一個container並加外距10
      child: Column(
        children: <Widget>[
          TextField(
            decoration: InputDecoration(labelText: 'Product Title'),
            //input的標籤
            onChanged: (String value) {
              setState(() {
                titleValue = value;
              });
            },
          ),
          TextField(
            maxLines: 4,
            //可以有很多行
            decoration: InputDecoration(labelText: 'Product Description'),
            onChanged: (String value) {
              setState(() {
                descriptionValue = value;
              });
            },
          ),
          TextField(
            keyboardType: TextInputType.number,
            //小鍵盤只有數字
            decoration: InputDecoration(labelText: 'Product Price'),
            onChanged: (String value) {
              setState(() {
                priceValue = double.parse(value);
                 //轉成小數
              });
            },
          ),
        ],
      ),
    );
  }
}

主題來源：
Learn Flutter & Dart to Build iOS & Android Apps