ListView是最常用的可滚动组件之一，它可以沿一个方向线性排布所有子组件，并且它也支持列表项懒加载（在需要时才会创建）。

我们看看ListView的默认构造函数定义：

ListView({
  ...  
  //可滚动widget公共参数
  Axis scrollDirection = Axis.vertical,
  bool reverse = false,
  ScrollController? controller,
  bool? primary,
  ScrollPhysics? physics,
  EdgeInsetsGeometry? padding,
  
  //ListView各个构造函数的共同参数  
  double? itemExtent, // 该参数如果不为null，则会强制children的“长度”为itemExtent的
  Widget? prototypeItem, //通知list 我所有的子项都和这个的高度一样 ,方便计算
  
  // 该属性表示是否根据子组件的总长度来设置ListView的长度
  //当ListView在一个无边界(滚动方向上)的容器中时，shrinkWrap必须为true。
  bool shrinkWrap = false, 
  
  bool addAutomaticKeepAlives = true,
  bool addRepaintBoundaries = true,
  double? cacheExtent, // 预渲染区域长度
    
  //子widget列表
  List children = const [],
})

class ListViewState1 extends StatelessWidget{

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return ListView(
      shrinkWrap: true,
      padding: EdgeInsets.all(20),
      children: const [
        Text('Im dedicating every day to you',style: TextStyle(height: 2),),
        Text('Domestic life was never quite my style',style: TextStyle(height: 2),),
        Text('When you smile, you knock me out, I fall apart',style: TextStyle(height: 2),),
        Text('And I thought I was so smart',style: TextStyle(height: 2),),
        Text('Im dedicating every day to you',style: TextStyle(height: 2),),
        Text('Domestic life was never quite my style',style: TextStyle(height: 2),),
        Text('When you smile, you knock me out, I fall apart',style: TextStyle(height: 2),),
        Text('And I thought I was so smart',style: TextStyle(height: 2),),
        Text('Im dedicating every day to you',style: TextStyle(height: 2),),
        Text('Domestic life was never quite my style',style: TextStyle(height: 2),),
        Text('When you smile, you knock me out, I fall apart',style: TextStyle(height: 2),),
        Text('And I thought I was so smart',style: TextStyle(height: 2),),

      ],
    );
  }
}

**ListView.builder** 适合列表项比较多或者列表项不确定的情况

```dart
itemBuilder：它是列表项的构建器
itemCount：列表项的数量，如果为null，则为无限列表。
```

// ListView.builder + prototypeItem +  itemCount 展示 
// ListTile 一个 简单的组件
class ListViewState3 extends StatelessWidget{

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return ListView.builder(
      prototypeItem: ListTile(title: Text("1")),
      itemCount: 56,
      itemBuilder: (context, index) {
        return ListTile(title: Text("$index"));
      },
    );
  }
}

ListView.separated

ListView.separated可以在生成的列表项之间添加一个分割组件，它比ListView.builder多了一个separatorBuilder参数，该参数是一个分割组件生成器。

class ListViewState4 extends StatelessWidget{

  //下划线widget预定义以供复用。
  Widget pider1=Divider(color: Colors.blue,);
  Widget pider2=Divider(color: Colors.green);

  List list2 = [
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5"];

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scrollbar(child: ListView.separated(
        itemCount: list2.length,
        itemBuilder: (BuildContext context ,int index){
          return ListTile(title: Text(list2[index]));
        },
        separatorBuilder: (BuildContext context, int index) {
          return index%2==0?pider1:pider2;
        },
    ));
  }
}

固定高度列表

给列表指定 itemExtent 或 prototypeItem 会有更高的性能，所以当我们知道列表项的高度都相同时，强烈建议指定 itemExtent 或 prototypeItem

实例 : 给一个listview 动态添加数据

1 动态添加需要 State 所有需要构建 StatefulWidget

class MyListViewState0 extends StatefulWidget {
  const MyListViewState0({Key? key}) : super(key: key);

  @override
  State createState() => _MyState0();
}

class _MyState0 extends State {

  // 初始化 数据源
  List list2 = [
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5",
    "1","2","3","4","5"];

  @override
  Widget build(BuildContext context) {
    return ConstrainedBox(
        constraints: BoxConstraints.tightFor(width: double.infinity),
        child: Column(

          children: [
            ElevatedButton(onPressed: (){
          		// 刷新state 
           		setState(() {
          			//点击按钮时 itemss 自加一 
                itemss ++ ;
          			// 添加到数据中 
                list2.insert(0, "-----------$itemss");
              });
            }, child: Text("点击1")),
            Expanded(child:  ListViewState2(list2))
          ],
        )
    );
  }
}

class ListViewState2 extends StatelessWidget{

  List list = [] ;

  ListViewState2(List item,{Key? key}) : super(key: key){
    list = item ;
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scrollbar(child: ListView.builder(
        itemCount: list.length,
        itemExtent: 50,
        itemBuilder: (BuildContext context ,int index){
          return Text(list[index]);
        }
    ));
  }
}