SliverAppBar 华丽的界面

  const SliverChildBuilderDelegate(
    this.builder, //  创建子元素 (BuildContext context, int index){return build}
    {
    this.findChildIndexCallback,  // 调用它，以便在重新排序时根据子元素的键查找新索引。如果没有提供，当子部件从[builder]返回的顺序发生变化时，子部件可能不会映射到它现有的[RenderObject]。这可能会导致状态损失。这个回调函数应该接受一个input [Key]，它应该返回子元素的索引(如果没有找到)。
    this.childCount,//  限制子孩子的个数
    this.addAutomaticKeepAlives = true,
    this.addRepaintBoundaries = true,
    this.addSemanticIndexes = true,
    this.semanticIndexCallback = _kDefaultSemanticIndexCallback,
    this.semanticIndexOffset = 0,
  }) : assert(builder != null),
       assert(addAutomaticKeepAlives != null),
       assert(addRepaintBoundaries != null),
       assert(addSemanticIndexes != null),
       assert(semanticIndexCallback != null);

基本用法

    return CustomScrollView(
      slivers: <Widget>[
        SliverAppBar(
           expandedHeight: 200.0,
           pinned: true, // 当滑动到底部的时候则显示标题
           leading: IconButton(icon: Icon(Icons.arrow_back_ios), color: Colors.red, onPressed: (){
           }),
           backgroundColor: Colors.black,
           flexibleSpace: FlexibleSpaceBar( // 背景
              title: Text('娜扎之魔童降世', style: TextStyle(
                color: Color(0xffe5e5e5),
                fontSize: 16,
              ),),
              background: Image.network(
                'https://ss1.bdstatic.com/70cFuXSh_Q1YnxGkpoWK1HF6hhy/it/u=3254228255,2309346508&fm=26&gp=0.jpg',
                  fit: BoxFit.fitHeight, // 沾满真个高度
              ),
           ),
        ),
        // SliverList(
        //   delegate: SliverChildBuilderDelegate((content, index) {
        //     return Container(
        //       height: 65,
        //       color: Colors.primaries[index % Colors.primaries.length],
        //     );
        //   }, childCount: 5),
        // )
        SliverFixedExtentList(
          delegate: SliverChildBuilderDelegate(
            (BuildContext context, int index){
              return Card(
                child: Container(
                  alignment: Alignment.center,
                  color: Colors.primaries[(index % 18)],
                  child: Text(index.toString()),
                ),
              );
            },
            childCount: 7, //  如不设置则无限个子孩子
            findChildIndexCallback: (key) => 0,
            semanticIndexOffset: 2
          ),
         itemExtent: 80.0)
      ],
    );