在颤振中用于空值错误的空检查运算符

Question

如何解决？

环境：sdk：">=2.12.0 <3.0.0"

这是一段具有空安全错误的代码，我试图从我的数据库中获取数据以显示为轮播滑块

 FutureBuilder(
                  future: getSlider,
                  builder: (BuildContext context,
                      AsyncSnapshot<List<ModelEbook>> snapshot) {
                    if (snapshot.connectionState == ConnectionState.done) {
                      //Create design in here
                      return SizedBox(
                        height: 27.0.h,
                        child: Swiper(
                          autoplay: true,
                          itemCount: snapshot.data!.length,
                          itemBuilder: (BuildContext context, int index) {
                            return GestureDetector(
                              onTap: () {},
                              child: Padding(
                                padding: EdgeInsets.all(10),
                                child: Container(
                                  child: Stack(
                                    children: [
                                      ClipRRect(
                                        child: Image.network(
                                          listSlider[index].photo,
                                          fit: BoxFit.cover,
                                          width: 100.0.w,
                                        ),
                                        borderRadius:
                                            BorderRadius.circular(15),
                                      ),
                                    ],
                                  ),
                                ),
                              ),
                            );
                          },
                        ),
                      );
                    } else {
                      return Container();
                    }
                  },
                ),

下面是调试控制台中加载的错误

════════ Exception caught by widgets library ═══════════════════════════════════
The following _CastError was thrown building FutureBuilder<List<ModelEbook>>(dirty, state: _FutureBuilderState<List<ModelEbook>>#8fb37):
Null check operator used on a null value

The relevant error-causing widget was
FutureBuilder<List<ModelEbook>>
When the exception was thrown, this was the stack
#0      _HomeState.build.<anonymous closure>. 
<anonymous closure>

#1      _FutureBuilderState.build
#2      StatefulElement.build
#3      ComponentElement.performRebuild
#4      StatefulElement.performRebuild
#5      Element.rebuild
#6      BuildOwner.buildScope
#7      WidgetsBinding.drawFrame
#8      SchedulerBinding._invokeFrameCallback
#9      SchedulerBinding.handleDrawFrame
(elided 3 frames from dart: async)

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Answer 1

您需要检查snapshot.data 。 这应该是这样的：

                if (snapshot.connectionState == ConnectionState.done) {
                      //Create design in here
                     if (snapshot.data == null) {
                        return Text('no data');
                     } else
                      return SizedBox(
                        height: 27.0.h,
                        child: Swiper(
                          autoplay: true,
                          itemCount: snapshot.data!.length,
                          itemBuilder: (BuildContext context, int index) {
                            /// ....