Flutter ListView豆瓣电影排行榜

今天我们要实现一个豆瓣的Top150页面，看下豆瓣的效果。

豆瓣Top150页面.png

我们实现的效果：

我们实现的效果

ListView，顾名思义，列表组件。

ListView水平方向

ListView({
    Key key,
//垂直还是水平方向
    Axis scrollDirection = Axis.vertical,
//列表数据是否翻转
    bool reverse = false,
//控制滚动的组件，比如：将listview滚动到某个位置，此时可以使用。
    ScrollController controller,
//
    bool primary,
    ScrollPhysics physics,
//listView的大小是否占满整个空间。false:占满，true：不占满
    bool shrinkWrap = false,
    EdgeInsetsGeometry padding,
    this.itemExtent,
    bool addAutomaticKeepAlives = true,
    bool addRepaintBoundaries = true,
    bool addSemanticIndexes = true,
    double cacheExtent,
//listview的内容，子组件。
    List<Widget> children = const <Widget>[],
    int semanticChildCount,
  })

shrinkWrap(bool)

shrinkWrap	效果
true	shrinkWrap-true.png
false	shrinkWrap-false.png

import 'package:flutter/material.dart';
import 'dart:math';

class FlutterListView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListView(
        children: getListWidgets());
  }
}

//生成listview children Widgets
List<Widget> getListWidgets() {
  List<ItemData> list = List();
  Random random = Random();
  for (int i = 0; i < 100; i++) {
    int r = random.nextInt(255);
    int g = random.nextInt(255);
    int b = random.nextInt(255);
    list.add(ItemData(Color.fromARGB(255, r, g, b), i.toString()));
  }
  return list.map((item) => ListViewItem(item)).toList();
}

class ListViewItem extends StatelessWidget {
  final ItemData itemData;

  ListViewItem(this.itemData);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: 150,
      height: 70,
      //ListTile可以作为listView的一种子组件类型，支持配置点击事件，一个拥有固定样式的Widget
      child: ListTile(
        leading: CircleAvatar(
          backgroundColor: itemData.color,
          child: Text(
            itemData.text,
            style: TextStyle(color: Colors.white),
          ),
        ),
        title: Text(itemData.text),
      ),
    );
  }
}

class ItemData {
  final Color color;
  final String text;

  ItemData(this.color, this.text);
}

ListView垂直方向

ListView也支持水平方向显示，设置Axis scrollDirection = Axis.horizontal,即可。

一般我们使用静态listview，也就是listview中的children较少的时候，一般会直接使用ListView的构造函数中的children，显示Widget。如果比如加载网络数据，listView数据量较多，listview的构建方式就不能直接使用默认构造方法去设置了。这时我们通过使用ListView的builder方法。

ListView.builder

ListView.builder({
    Key key,
    Axis scrollDirection = Axis.vertical,
    bool reverse = false,
    ScrollController controller,
    bool primary,
    ScrollPhysics physics,
    bool shrinkWrap = false,
    EdgeInsetsGeometry padding,
    this.itemExtent,
    @required IndexedWidgetBuilder itemBuilder,
//listView的item数量
    int itemCount,
    bool addAutomaticKeepAlives = true,
    bool addRepaintBoundaries = true,
    bool addSemanticIndexes = true,
    double cacheExtent,
    int semanticChildCount,
  })

itemBuilder

typedef IndexedWidgetBuilder = Widget Function(BuildContext context, int index);
可以看到itemBuilder是一个方法对象，参数为：(BuildContext context, int index)，返回值是Widget，也就是listView的子item。

ListView.builder(
      //item 的数量，subjects为我们自己的数据源。
        itemCount: subjects.length,
        itemBuilder: (BuildContext context, int index) {
          return Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
               return Text('Hello')
            ],
          );
        });

使用起来还是比较简单的。

下方高能能，直接开始讲如何写一个豆瓣Top150页面

import 'dart:convert' as Convert;
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';

class DouBanListView extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return DouBanState();
  }
}

class DouBanState extends State<DouBanListView> {
  var subjects = [];

  var itemHeight = 150.0;

  requestMovieTop() async {
    var httpClient = new HttpClient();
    //http://api.douban.com/v2/movie/top250?start=25&count=10
    var uri = new Uri.http(
        'api.douban.com', '/v2/movie/top250', {'start': '0', 'count': '150'});
    var request = await httpClient.getUrl(uri);
    var response = await request.close();
    var responseBody = await response.transform(Convert.utf8.decoder).join();
    Map data = Convert.jsonDecode(responseBody);
    setState(() {
      subjects = data['subjects'];
    });
  }

  @override
  void initState() {
    requestMovieTop();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: getListViewContainer(),
    );
  }

  getListViewContainer() {
    if (subjects.length == 0) {
      //loading
      return CupertinoActivityIndicator();
    }
    return ListView.builder(
      //item 的数量
        itemCount: subjects.length,
        itemBuilder: (BuildContext context, int index) {
          return Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              numberWidget(index+1),
              getItemContainerView(subjects[index]),
              //下面的灰色分割线
              Container(
                height: 10,
                color: Color.fromARGB(255, 234, 233, 234),
              )
            ],
          );
        });
  }

  //肖申克的救赎(1993) View
  getTitleView(subject) {
    var title = subject['title'];
    var year = subject['year'];
    return Container(
      child: Row(
        children: <Widget>[
          Icon(
            Icons.play_circle_outline,
            color: Colors.redAccent,
          ),
          Text(
            title,
            style: TextStyle(
                fontSize: 18, fontWeight: FontWeight.bold, color: Colors.black),
          ),
          Text('($year)',
              style: TextStyle(
                  fontSize: 16,
                  fontWeight: FontWeight.bold,
                  color: Colors.grey))
        ],
      ),
    );
  }

  getItemContainerView(var subject) {
    var imgUrl = subject['images']['medium'];
    return Container(
      width: double.infinity,
      padding: EdgeInsets.all(5.0),
      child: Row(
        children: <Widget>[
          getImage(imgUrl),
          Expanded(
            child: getMovieInfoView(subject),
            flex: 1,
          )
        ],
      ),
    );
  }

  //圆角图片
  getImage(var imgUrl) {
    return Container(
      decoration: BoxDecoration(
          image:
              DecorationImage(image: NetworkImage(imgUrl), fit: BoxFit.cover),
          borderRadius: BorderRadius.all(Radius.circular(5.0))),
      margin: EdgeInsets.only(left: 8, top: 3, right: 8, bottom: 3),
      height: itemHeight,
      width: 100.0,
    );
  }

  getStaring(var stars) {
    return Row(
      children: <Widget>[RatingBar(stars), Text('$stars')],
    );
  }

  //电影标题，星标评分，演员简介Container
  getMovieInfoView(var subject) {
    var start = subject['rating']['average'];
    return Container(
      height: itemHeight,
      alignment: Alignment.topLeft,
      child: Column(
        children: <Widget>[
          getTitleView(subject),
          RatingBar(start),
          DescWidget(subject)
        ],
      ),
    );
  }

  //NO.1 图标
  numberWidget(var no) {
    return Container(
      child: Text(
        'No.$no',
        style: TextStyle(color: Color.fromARGB(255, 133, 66, 0)),
      ),
      decoration: BoxDecoration(
          color: Color.fromARGB(255, 255, 201, 129),
          borderRadius: BorderRadius.all(Radius.circular(5.0))),
      padding: EdgeInsets.fromLTRB(8, 4, 8, 4),
      margin: EdgeInsets.only(left: 12, top: 10),
    );
  }
}

//类别、演员介绍
class DescWidget extends StatelessWidget {
  var subject;

  DescWidget(this.subject);

  @override
  Widget build(BuildContext context) {
    var casts = subject['casts'];
    var sb = StringBuffer();
    var genres = subject['genres'];
    for (var i = 0; i < genres.length; i++) {
      sb.write('${genres[i]}  ');
    }
    sb.write("/ ");
    List<String> list = List.generate(
        casts.length, (int index) => casts[index]['name'].toString());

    for (var i = 0; i < list.length; i++) {
      sb.write('${list[i]} ');
    }
    return Container(
      child: Text(
        sb.toString(),
        softWrap: true,
        textDirection: TextDirection.ltr,
        style:
            TextStyle(fontSize: 16, color: Color.fromARGB(255, 118, 117, 118)),
      ),
    );
  }
}

class RatingBar extends StatelessWidget {
  double stars;

  RatingBar(this.stars);

  @override
  Widget build(BuildContext context) {
    List<Widget> startList = [];
    //实心星星
    var startNumber = stars ~/ 2;
    //半实心星星
    var startHalf = 0;
    if (stars.toString().contains('.')) {
      int tmp = int.parse((stars.toString().split('.')[1]));
      if (tmp >= 5) {
        startHalf = 1;
      }
    }
    //空心星星
    var startEmpty = 5 - startNumber - startHalf;

    for (var i = 0; i < startNumber; i++) {
      startList.add(Icon(
        Icons.star,
        color: Colors.amberAccent,
        size: 18,
      ));
    }
    if (startHalf > 0) {
      startList.add(Icon(
        Icons.star_half,
        color: Colors.amberAccent,
        size: 18,
      ));
    }
    for (var i = 0; i < startEmpty; i++) {
      startList.add(Icon(
        Icons.star_border,
        color: Colors.grey,
        size: 18,
      ));
    }
    startList.add(Text(
      '$stars',
      style: TextStyle(
        color: Colors.grey,
      ),
    ));
    return Container(
      alignment: Alignment.topLeft,
      padding: const EdgeInsets.only(left: 0, top: 8, right: 0, bottom: 5),
      child: Row(
        children: startList,
      ),
    );
  }
}

最终效果：

我们实现的效果

listview点击事件

点击事件，使用的是GestureDetector,这是Flutter中的手势处理Widget。

ListView.builder(
        //item 的数量
        itemCount: subjects.length,
        itemBuilder: (BuildContext context, int index) {
          return GestureDetector(//Flutter 手势处理
            child: Container(
              color: Colors.transparent,
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  numberWidget(index + 1),
                  getItemContainerView(subjects[index]),
                  //下面的灰色分割线
                  Container(
                    height: 10,
                    color: Color.fromARGB(255, 234, 233, 234),
                  )
                ],
              ),
            ),
            onTap: () {
              //监听点击事件
              print("click item index=$index");
            },
          );
        });

listview点击单个条目.gif

总体来说，上手ListView还是比较简单的。只不过，在listView的item的布局排列中，可能看的不是太懂。如果有不太理解的，可以看看我的前面几篇博客。这里用到的属性，布局方式，之前都有讲过。
博客地址