flutter - “The method '其中带firestore flutter的streambuilder时的' was called on null.”

Question

我正在使用StreamBuilder从Firestore流一些数据。

它工作正常，并且正在显示数据，但控制台中存在错误。

我认为这可能是包含错误的代码:

Padding(
                  padding: const EdgeInsets.symmetric(horizontal: 16),
                  child: Consumer<AppState>(
                    builder: (context, appState, _) =>
                        StreamBuilder<List<Dentist>>(
                      stream: database.dentistsStream(),
                      builder: (context, snapshot) => Column(
                        children: <Widget>[
                          for (final dentist in snapshot.data.where((e) => e
                              .categoryIds
                              .contains(appState.selectedCategoryId)))
                            GestureDetector(
                              onTap: () {},
                              child: DentistItem(
                                dentist: dentist,
                              ),
                            ),
                        ],
                      ),
                    ),
                  ),
                ),

和错误:

enter image description here

有帮助吗？

注意:我知道Dart的旧版本不支持此处的“for”。

Answer 1

在根据快照创建列之前，请确保快照具有数据if (snapshot.hasData)；

Padding(
  padding: const EdgeInsets.symmetric(horizontal: 16),
  child: Consumer<AppState>(
    builder: (context, appState, _) => StreamBuilder<List<Dentist>>(
      stream: database.dentistsStream(),
      builder: (context, snapshot) {
        if (snapshot.hasData)
          return Column(
            children: <Widget>[
              for (final dentist in snapshot.data.where((e) =>
                  e.categoryIds.contains(appState.selectedCategoryId)))
                GestureDetector(
                  onTap: () {},
                  child: DentistItem(
                    dentist: dentist,
                  ),
                ),
            ],
          );
        return Center(child: CircularProgressIndicator());
      },
    ),
  ),
)