在null上调用了“ findRenderObject”。带Key.currentContext.findRenderObject（）的SliverList，

Question

我正在尝试制作一个粘性TabBar，当我按任意它的选项卡时，将我向下滚动到它的一部分，我使用了用于粘性条的条子和用于滚动的键来实现。它正在工作，但是当我从顶部到最低的底部，或者反之亦然，或者当我的零件高度很高时，它告诉我'findRenderObject'在null上被调用。

这是我的银条委托人代码

class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  _SliverAppBarDelegate({
    @required this.minHeight,
    @required this.maxHeight,
    @required this.child,
  });
  final double minHeight;
  final double maxHeight;
  final Widget child;
  @override
  double get minExtent => minHeight;
  @override
  double get maxExtent => math.max(maxHeight, minHeight);
  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return new SizedBox.expand(child: child);
  }

  @override
  bool shouldRebuild(_SliverAppBarDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}

这是我的条子小部件主体代码

body: CustomScrollView(
    controller: scrollController,
    slivers: <Widget>[
      SliverList(
        delegate: SliverChildListDelegate(
          [
            Container(
                height: data.size.height / 3,
                child: new Swiper(
                  itemBuilder: (BuildContext context, int index) {
                    return new Image.asset(
                      imgs[index],
                      fit: BoxFit.fill,
                    );
                  },
                  indicatorLayout: PageIndicatorLayout.COLOR,
                  autoplay: true,
                  itemCount: imgs.length,
                  pagination: new SwiperPagination(
                      margin: new EdgeInsets.all(5.0),
                      builder: new DotSwiperPaginationBuilder(
                          color: Colors.grey.shade400,
                          activeColor: yumColors.pink)),
                )),
          ],
        ),
      ),
      makeTabBarHeader(),
      SliverList(
        key: sliverListtKey,
        delegate: SliverChildListDelegate(
          [
            Padding(padding: const EdgeInsets.all(8.0), child: Container()),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: Container(
                height: 900,
                child: Card(
                  color: yumColors.pink,
                  key: overKey,
                  child: Center(
                      child: Text(
                    "Overview",
                    style: TextStyle(
                        color: Colors.white,
                        fontSize: 3 * SizeConfig.textMultiplier),
                  )),
                ),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: Container(
                height: 900,
                child: Card(
                  key: revKey,
                  color: yumColors.pink,
                  child: Center(
                      child: Text(
                    "Reviews",
                    style: TextStyle(
                        color: Colors.white,
                        fontSize: 3 * SizeConfig.textMultiplier),
                  )),
                ),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: Container(
                height: 900,
                child: Card(
                  key: menuKey,
                  color: yumColors.pink,
                  child: Center(
                      child: Text(
                    "Menu",
                    style: TextStyle(
                        color: Colors.white,
                        fontSize: 3 * SizeConfig.textMultiplier),
                  )),
                ),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(8.0),
              child: Container(
                height: 900,
                child: Card(
                  key: contactKey,
                  color: yumColors.pink,
                  child: Center(
                      child: Text(
                    "Contact",
                    style: TextStyle(
                        color: Colors.white,
                        fontSize: 3 * SizeConfig.textMultiplier),
                  )),
                ),
              ),
            ),
            Padding(padding: const EdgeInsets.all(8.0), child: Container()),
          ],
        ),
      ),
    ],
  ),
);

} }

这是我的粘性标签栏代码

  SliverPersistentHeader makeTabBarHeader() {
return SliverPersistentHeader(
  pinned: true,
  delegate: _SliverAppBarDelegate(
    minHeight: 60.0,
    maxHeight: 60.0,
    child: Container(
      color: Colors.white,
      child: TabBar(
        onTap: (val) {
          switch (val) {
            case 0:
              {
                scrollController.position.ensureVisible(
                  overKey.currentContext.findRenderObject(),
                  alignment:
                  0.0, // How far into view the item should be scrolled (between 0 and 1).
                  duration: const Duration(seconds: 1),
                );
              }
              break;
            case 1:
              {
                scrollController.position.ensureVisible(
                  revKey.currentContext.findRenderObject(),
                  alignment:
                      0.0, // How far into view the item should be scrolled (between 0 and 1).
                  duration: const Duration(seconds: 1),
                );
              }
              break;
            case 2:
              {
                scrollController.position.ensureVisible(
                  menuKey.currentContext.findRenderObject(),
                  alignment:
                      0.0, // How far into view the item should be scrolled (between 0 and 1).
                  duration: const Duration(seconds: 1),
                );
              }
              break;
            case 3:
              {
                scrollController.position.ensureVisible(
                  contactKey.currentContext.findRenderObject(),
                  alignment:
                      0.0, // How far into view the item should be scrolled (between 0 and 1).
                  duration: const Duration(seconds: 1),
                );
              }
              break;
          }
        },
        unselectedLabelColor: Colors.grey.shade700,
        indicatorColor: yumColors.pink,
        indicatorWeight: 2.0,
        labelColor: yumColors.pink,
        controller: _tabController,
        tabs: <Widget>[
          new Tab(
            child: Text(
              "Overview",
              style: TextStyle(
                  fontWeight: FontWeight.w600,
                  fontSize: 1.6 * SizeConfig.textMultiplier),
            ),
          ),
          new Tab(
            child: Text(
              "Reviews",
              style: TextStyle(
                  fontWeight: FontWeight.w600,
                  fontSize: 1.6 * SizeConfig.textMultiplier),
            ),
          ),
          new Tab(
            child: Text(
              "Menu",
              style: TextStyle(
                  fontWeight: FontWeight.w600,
                  fontSize: 1.6 * SizeConfig.textMultiplier),
            ),
          ),
          new Tab(
            child: Text(
              "Contact",
              style: TextStyle(
                  fontWeight: FontWeight.w600,
                  fontSize: 1.6 * SizeConfig.textMultiplier),
            ),
          ),
        ],
        indicatorSize: TabBarIndicatorSize.tab,
      ),
    ),
  ),
);

}