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 DefaultTextStyle(
        style: TextStyle(fontSize: 28, color: Colors.red),
        child: CustomScrollView(
          ///视窗 里面比外边大的一个东西哦哦、
          slivers: <Widget>[
            SliverAppBar(
              floating: true, //往下拉时第一时间显示标题 配合snap使用
              // pinned: true, //一直显示
              snap: true, //轻轻一拉就都显示
              stretch: true, //允许向下拉伸
              title: Text("标题"),
              expandedHeight: 200,
              flexibleSpace: FlexibleSpaceBar(
                background: FlutterLogo(),
                title: Text("FlexibleSpaceBar标题"),
                stretchModes: [
                  StretchMode.blurBackground, //模糊背景
                  StretchMode.fadeTitle, StretchMode.zoomBackground,

                  //下拉杉,拉伸的时候出现的效果
                ],
                collapseMode: CollapseMode.parallax, //缩回去的时候 的效果
              ),
            ),
            SliverToBoxAdapter(
              child: Placeholder(),
            ),

            SliverList(
                delegate: SliverChildListDelegate([
              FlutterLogo(
                size: 200,
              ),
              FlutterLogo(
                size: 600,
              ),
              FlutterLogo()
            ]))

            ///用于固定元素尺寸的列表
          ],
        ),
      )
  SliverOpacity(
              opacity: 0.9,
              sliver: SliverToBoxAdapter(
                child: FlutterLogo(
                  size: 500,
                ),
              ),
            ),
 SliverAnimatedOpacity(
              duration: Duration(
                seconds: 100,
              ),
              opacity: 0.9,
              sliver: SliverToBoxAdapter(
                child: FlutterLogo(
                  size: 500,
                ),
              ),
            ),
SliverIgnorePointer(
              ignoring: false,
              sliver: SliverToBoxAdapter(
                child: FlatButton(
                  onPressed: () {},
                  child: FlutterLogo(
                    size: 500,
                  ),
                ),
              ),
            ),
 SliverList(
                delegate: SliverChildListDelegate([
              FlutterLogo(
                size: 200,
              ),
              FlutterLogo(
                size: 600,
              ),
              FlutterLogo()
            ])),
SliverGrid(
              delegate: SliverChildListDelegate([
                Icon(
                  Icons.ac_unit,
                ),
                Icon(
                  Icons.ac_unit,
                ),
                Icon(
                  Icons.ac_unit,
                ),
              ]),
              gridDelegate: SliverGridDelegateWithMaxCrossAxisExtent(
                maxCrossAxisExtent: 80,
              ),
            ),
SliverPadding(
              padding: EdgeInsets.all(10),
              sliver: SliverIgnorePointer(
                ignoring: false,
                sliver: SliverToBoxAdapter(
                  child: FlatButton(
                    onPressed: () {},
                    child: FlutterLogo(
                      size: 500,
                    ),
                  ),
                ),
              ),
            ),
 SliverToBoxAdapter(
              child: Divider(),
            ),
            SliverToBoxAdapter(),
   //当前视窗
            SliverFillRemaining(
              child: Placeholder(),
            )
SliverFillRemaining(
              child: Center(
                child: CircularProgressIndicator(),
              ),
            )
            
            
            

 SliverLayoutBuilder(
              builder: (context, constraints) {
                print(constraints);
                return SliverToBoxAdapter();
              },
            )
 SliverConstraints(
              
            ),            ),