拦截返回键时无法获取WatchSkSelectClubBloc问题求助

问题描述 #

拦截返回键时希望将主Bloc的状态重置为初始状态，因此在按下返回键时添加重置事件，但操作无法正常执行。报错提示BlocProvider.of()调用的context中不存在WatchSkSelectClubBloc，尽管Widget Tree显示该Bloc已被提供，且该模块断点无效。

报错堆栈 #

_onBackPressed Builder Builder(dependencies: [ScrollConfiguration, _LocalizationsScope-[GlobalKey#488f2]])

======== Exception caught by gesture ===============================================================
The following assertion was thrown while handling a gesture:
        BlocProvider.of() called with a context that does not contain a WatchSkSelectClubBloc.

        No ancestor could be found starting from the context that was passed to BlocProvider.of().

        This can happen if the context you used comes from a widget above the BlocProvider.

        The context used was: Builder(dependencies: [ScrollConfiguration, _LocalizationsScope-[GlobalKey#488f2]])
        ...

调用Widget代码 #

Navigator.of(context).push(
  MaterialPageRoute(
      builder: (context) =>
          WatchSkSelectTornooiPage(
            parentContext: context,
            clubname:
            state.clickedOnClubnameFromDbForWedstrijdtafel,
            anonymousAllowed: true,
            activeWts: state.activeWts,
            tournamentId:
            state.clickedOnTournamentIdFromDbForWedstrijdtafel,
          )),
);

抛出异常的代码 #

class WatchSkSelectTornooiPage extends StatefulWidget {
  final BuildContext parentContext;
  ...
  void _onBackPressed(context) {
    // Set state back to init to refresh clublist
    if (kDebugMode) {
      print("_onBackPressed ${widget.parentContext} ${context}");
    }
    BlocProvider.of<WatchSkSelectClubBloc>(context)
        .add(WatchSkRefreshSelectClubEvent());
    Navigator.of(context).pop();
  }
  ...
}

问题原因与解决方案 #

原因 #

_onBackPressed方法中使用的context是当前WatchSkSelectTornooiPage页面的上下文，而WatchSkSelectClubBloc是在父页面的Widget树中提供的，当前页面的上下文无法向上查找到该Bloc实例。虽然你已经将父页面的parentContext传入当前页面，但代码中并未使用它来获取Bloc。

解决方案 #

直接使用传入的parentContext来获取Bloc实例，修改_onBackPressed方法：

void _onBackPressed(context) {
  // Set state back to init to refresh clublist
  if (kDebugMode) {
    print("_onBackPressed ${widget.parentContext} ${context}");
  }
  // 使用父页面的context获取Bloc
  BlocProvider.of<WatchSkSelectClubBloc>(widget.parentContext)
      .add(WatchSkRefreshSelectClubEvent());
  Navigator.of(context).pop();
}

额外验证：确保传入的parentContext确实处于BlocProvider<WatchSkSelectClubBloc>的子树中，也就是父页面的context是在BlocProvider创建之后的上下文，这样才能正确找到Bloc实例。

内容的提问来源于stack exchange，提问作者Hoegje