Flutter 无法滚动到颤振中的特定小部件

所以，当用户按下按钮时，我想滚动到一个特定的小部件。为此，我给小部件分配了一个键，然后使用它来获取renderobject，从而移动到该小部件。但是我得到了错误：-

NoSuchMethodError: invalid member on null: 'findRenderObject'

GlobalKey ourServices= GlobalKey();
GlobalKey ourProducts= GlobalKey();
ScrollController controller = new ScrollController();

Container(
            height: MediaQuery.of(context).size.height,
            width: double.infinity,
            decoration: BoxDecoration(
              image: DecorationImage(
                image: AssetImage('assets/coverPhoto.jpg'),
                fit: BoxFit.cover,
              ),
            ),
            child: CustomScrollView(
              controller: controller,
              slivers: [
                SliverAppBar(
                  floating: false,
                  expandedHeight: MediaQuery.of(context).size.height*1.8/3,
                  elevation: 0.0,
                  backgroundColor: Colors.transparent,
                  flexibleSpace: FlexibleSpaceBar(
                    centerTitle: true,
                    title: Text("Heading")
                  ),
                ),
                SliverList(
                  delegate: SliverChildListDelegate(
                    [
                      SizedBox(height: MediaQuery.of(context).size.height/4,),
                      OurServices(key: ourServices,),
                      OurProducts(key: ourProducts,),
                      ContactUs(key: contactUs,),
                    ],
                  ),
                ),
              ],
            ),
          ),

代码：-

NoSuchMethodError: invalid member on null: 'findRenderObject'

GlobalKey ourServices= GlobalKey();
GlobalKey ourProducts= GlobalKey();
ScrollController controller = new ScrollController();

Container(
            height: MediaQuery.of(context).size.height,
            width: double.infinity,
            decoration: BoxDecoration(
              image: DecorationImage(
                image: AssetImage('assets/coverPhoto.jpg'),
                fit: BoxFit.cover,
              ),
            ),
            child: CustomScrollView(
              controller: controller,
              slivers: [
                SliverAppBar(
                  floating: false,
                  expandedHeight: MediaQuery.of(context).size.height*1.8/3,
                  elevation: 0.0,
                  backgroundColor: Colors.transparent,
                  flexibleSpace: FlexibleSpaceBar(
                    centerTitle: true,
                    title: Text("Heading")
                  ),
                ),
                SliverList(
                  delegate: SliverChildListDelegate(
                    [
                      SizedBox(height: MediaQuery.of(context).size.height/4,),
                      OurServices(key: ourServices,),
                      OurProducts(key: ourProducts,),
                      ContactUs(key: contactUs,),
                    ],
                  ),
                ),
              ],
            ),
          ),

我的滚动按钮中的代码是：-

GestureDetector(
            onTap: ()=>controller.position.ensureVisible(
              ourServices.currentContext.findRenderObject(),
              alignment: 0.5,
              duration: const Duration(seconds: 1),
            ),
            child: Text("Services",style: TextStyle(fontSize: 16.0,fontWeight: FontWeight.w500,color: Colors.white),),
          ),