Flutter实现瀑布流效果（GridView部件不固定高度）

落日映苍穹つ 2023-02-15 12:35 464阅读 0赞

### Flutter实现瀑布流效果 ###

*  引言
 *   *  安装 flutter\_staggered\_grid\_view
     *  布局中使用 flutter\_staggered\_grid\_view
     *   *  card\_page.dart 父级页面
         *  square\_card\_item.dart 子部件
         *  卡片数据模型

# 引言 #

Flutter APP 中实现瀑布流布局展示商品信息。效果图：  
  
![在这里插入图片描述][20200605144947664.gif_pic_center]

## 安装 flutter\_staggered\_grid\_view ##

Flutter自带的网格布局部件固定了每个子部件的高度，不能实现我们的需求。GridView 部件：如下图所示：  
  
![在这里插入图片描述][2020060512031097.png_pic_center]  
要想实现瀑布流效果需要使用第三方包： [flutter\_staggered\_grid\_view][flutter_staggered_grid_view]

## 布局中使用 flutter\_staggered\_grid\_view ##

为了便于代码的阅读和拓展，减少嵌套理清业务逻辑（文邹邹的理论。。。），实际上就是把 GridView部件的父级页面和他的子项布局写在两个文件里面。

### card\_page.dart 父级页面 ###

这里面主要实例化封装好的 Dio 类来请求获取商品数据和编写父别页面布局。

import 'package:flutter/material.dart';
    import 'package:flutter/cupertino.dart';
    import 'package:oblivion/public.dart';
    import 'package:flutter_screenutil/flutter_screenutil.dart';
    import 'package:flutter_staggered_grid_view/flutter_staggered_grid_view.dart';
    import 'package:oblivion/widgets/square_card.dart';
    import 'package:oblivion/model/CardModel.dart';
    
    
    class CardPage extends StatefulWidget { 
      @override
      _CardPageState createState() => _CardPageState();
    }
    
    class _CardPageState extends State<CardPage> { 
      List cardList;
      //获取商品数据
      Future getSquarePageContent() async{ 
        DioManager.getInstance().postNoParams(ServiceUrl.getCards,(data) { 
          setState(() { 
          	//商品列表
            cardList =(data['data']['cards'] as List).cast();
          });
        }, (error) { 
          print("接口异常：" + error);
        });
      }
    
      @override
      void initState() { 
        // TODO: implement initState
        getSquarePageContent();
        super.initState();
      }
      //下拉刷新方法
      Future<void> _onRefresh() async { 
        print("_onRefresh");
      }
      //上拉加载方法
      Future<void> _onLoadMore() async { 
        print("_onLoadMore");
      }
      @override
      Widget build(BuildContext context) { 
        if(cardList == null){ 
          return Text('没有数据');
        }else{ 
          return Container(
            height: ScreenUtil().setHeight(1500),
            padding:EdgeInsets.all(3.0),
            child:  StaggeredGridView.countBuilder(
              padding: EdgeInsets.all(8),
              crossAxisCount: 4,
              itemCount: cardList.length,
              //核心代码，将Cards模型对象作为参数传递 
              itemBuilder: (BuildContext context, int index) { 
                var item = new Cards.fromJson(cardList[index]);
                return CardItem(item);
              },
              staggeredTileBuilder: (index) => StaggeredTile.fit(2),
              mainAxisSpacing: 4.0,
              crossAxisSpacing: 4.0,
            ),
          );
        }
      }
    }

### square\_card\_item.dart 子部件 ###

这部分主要从数据模型取出数据，编写每一个子项的页面布局。

import 'package:flutter/material.dart';
    import 'package:oblivion/model/CardModel.dart';
    import 'package:flutter_screenutil/flutter_screenutil.dart';
    import 'package:transparent_image/transparent_image.dart';
    class CardItem extends StatefulWidget { 
    
      CardItem(this.item);
    
      final Cards item;
    
      @override
      _CardItemState createState() { 
        return _CardItemState();
      }
    }
    
    class _CardItemState extends State<CardItem> { 
    
      _CardItemState();
    
      @override
      Widget build(BuildContext context) { 
        return Card(
            child: InkWell(
              onTap: (){ 
                // 跳转到商品详情
                print('点击了一件商品');
              },
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                mainAxisAlignment: MainAxisAlignment.start,
                children: <Widget>[
                  // 图片
                  Container(
                      width: double.infinity,
                      color: Colors.grey,
                      child:FadeInImage.assetNetwork(
                        placeholder: 'assets/images/loader.gif',
                        image: widget.item.img,//这里是网络图片
                        fit: BoxFit.fill,
                      ),
                  ),
                  // 描述
                  Container(
                      padding: EdgeInsets.fromLTRB(5, 5, 5, 0),
                      child: Text(widget.item.des,
                        maxLines: 2,
                        overflow: TextOverflow.ellipsis,
                      )
                  ),
    
                  Container(
                    height: ScreenUtil().setHeight(80),
                      padding: EdgeInsets.fromLTRB(5, 0, 5, 0),
                      child: Align(
                        alignment: Alignment.bottomLeft,
                        heightFactor: 2,
                        widthFactor: 2,
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.spaceBetween,
                          children: <Widget>[
                            // 价钱和想要人数
                            Text("￥${widget.item.price.toString()}",style:TextStyle(color:Colors.pink)),
                            Text("${widget.item.want.toString()}人想要",style:TextStyle(fontSize: 10)),
                          ],
                        ),
                      ),
                  ),
                  Padding(
                      padding: EdgeInsets.all(1.0),
                      child: new Divider()
                  ),
                  Container(
                    height: ScreenUtil().setHeight(160),
                    padding: EdgeInsets.fromLTRB(5, 0, 5, 0),
                    child: Align(
                      alignment: Alignment.bottomLeft,
                      heightFactor: 2,
                      widthFactor: 2,
                      child: Row(
                        mainAxisAlignment: MainAxisAlignment.start,
                        children: <Widget>[
                          // 价钱和想要
                          Padding(
                            padding: EdgeInsets.only(top: 6),
                            child: Column(
                              children: <Widget>[
                                Image.network(
                                  widget.item.img,
                                  fit: BoxFit.fill,
                                  height: ScreenUtil().setHeight(110),
                                  width: ScreenUtil().setWidth(80),
                                ),
                              ],
                            ),
                          ),
                          Padding(
                            padding: EdgeInsets.fromLTRB(6, 0, 0, 0),
                            child: Center(
                               child: Text(widget.item.username,style:TextStyle(color:Colors.black)),
                            ),
                          )
    
                        ],
                      ),
                    ),
                  ),
                ],
              ),
            )
        );
      }
    }

### 卡片数据模型 ###

class CardModel { 
      List<Cards> _cards;
    
      CardModel({ List<Cards> cards}) { 
        this._cards = cards;
      }
    
      List<Cards> get cards => _cards;
      set cards(List<Cards> cards) => _cards = cards;
    
      CardModel.fromJson(Map<String, dynamic> json) { 
        if (json['cards'] != null) { 
          _cards = new List<Cards>();
          json['cards'].forEach((v) { 
            _cards.add(new Cards.fromJson(v));
          });
        }
      }
    
      Map<String, dynamic> toJson() { 
        final Map<String, dynamic> data = new Map<String, dynamic>();
        if (this._cards != null) { 
          data['cards'] = this._cards.map((v) => v.toJson()).toList();
        }
        return data;
      }
    }
    
    class Cards { 
      String _img;
      String _des;
      int _price;
      int _want;
      String _username;
    
      Cards({ String img, String des, int price, int want, String username}) { 
        this._img = img;
        this._des = des;
        this._price = price;
        this._want = want;
        this._username = username;
      }
    
      String get img => _img;
      set img(String img) => _img = img;
      String get des => _des;
      set des(String des) => _des = des;
      int get price => _price;
      set price(int price) => _price = price;
      int get want => _want;
      set want(int want) => _want = want;
      String get username => _username;
      set username(String username) => _username = username;
    
      Cards.fromJson(Map<String, dynamic> json) { 
        _img = json['img'];
        _des = json['des'];
        _price = json['price'];
        _want = json['want'];
        _username = json['username'];
      }
    
      Map<String, dynamic> toJson() { 
        final Map<String, dynamic> data = new Map<String, dynamic>();
        data['img'] = this._img;
        data['des'] = this._des;
        data['price'] = this._price;
        data['want'] = this._want;
        data['username'] = this._username;
        return data;
      }
    }

JSON格式

{ 
    	"cards": [{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_1.jpg",
    			"des": "美国短毛猫是原产于美国的一种猫，其祖先为欧洲早期移民带到北美的猫种，并与英国短毛猫和欧洲短毛猫同类。美国短毛猫的身体匀称、有力量，且活泼温顺。幼年短毛猫圆头圆脑，软绵绵的手感和灵活的四肢很是讨人喜欢",
    			"price": 111.00,
    			"want": 122,
    			"username": "美羊羊"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_2.jpg",
    			"des": "布偶猫是猫中较大、较重的一种。它的头呈V形，眼大而圆，被毛丰厚，四肢粗大，尾长，身体柔软，多为三色或双色猫。",
    			"price": 111.00,
    			"want": 1000,
    			"username": "小窝"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_3.jpg",
    			"des": "布偶猫是猫中较大、较重的一种。它的头呈V形，眼大而圆，被毛丰厚，四肢粗大，尾长，身体柔软，多为三色或双色猫。",
    			"price": 111.00,
    			"want": 122,
    			"username": "海绵宝宝"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_4.jpg",
    
    			"des": "美国短毛猫是原产于美国的一种猫，其祖先为欧洲早期移民带到北美的猫种，并与英国短毛猫和欧洲短毛猫同类。美国短毛猫的身体匀称、有力量，且活泼温顺。幼年短毛猫圆头圆脑，软绵绵的手感和灵活的四肢很是讨人喜欢",
    			"price": 111.00,
    			"want": 122,
    			"username": "流传风"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_5.jpg",
    			"des": "美国短毛猫是原产于美国的一种猫，其祖先为欧洲早期移民带到北美的猫种，并与英国短毛猫和欧洲短毛猫同类。美国短毛猫的身体匀称、有力量，且活泼温顺。幼年短毛猫圆头圆脑，软绵绵的手感和灵活的四肢很是讨人喜欢",
    			"price": 111.00,
    			"want": 122,
    			"username": "大发明家"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_6.jpg",
    			"des": "美国短毛猫是原产于美国的一种猫，其祖先为欧洲早期移民带到北美的猫种，并与英国短毛猫和欧洲短毛猫同类。美国短毛猫的身体匀称、有力量，且活泼温顺。幼年短毛猫圆头圆脑，软绵绵的手感和灵活的四肢很是讨人喜欢",
    			"price": 111.00,
    			"want": 122,
    			"username": "冰封凤凰"
    		},
    		{ 
    			"img": "http://scrutiny.geekadpt.cn/v1/images/card_1.jpg",
    			"des": "美国短毛猫是原产于美国的一种猫，其祖先为欧洲早期移民带到北美的猫种，并与英国短毛猫和欧洲短毛猫同类。美国短毛猫的身体匀称、有力量，且活泼温顺。幼年短毛猫圆头圆脑，软绵绵的手感和灵活的四肢很是讨人喜欢",
    			"price": 111.00,
    			"want": 122,
    			"username": "宇宙星神"
    		}
    	]
    }

[20200605144947664.gif_pic_center]: https://img-blog.csdnimg.cn/20200605144947664.gif#pic_center
[2020060512031097.png_pic_center]: https://img-blog.csdnimg.cn/2020060512031097.png#pic_center
[flutter_staggered_grid_view]: https://github.com/letsar/flutter_staggered_grid_view