即使没有状态更改，Flutter Bloc Listener 也在重建

Question

I have an App which uses a bottom navigation bar to switch between pages. To do this, I'm using Bloc . On one of the tab pages, I render a list with some items in it. This list is built when the State changes to SchedulesLoaded(see picture).

The problem I have is that when I'm changing pages using the bottom navigation bar(Which is using a completely different Bloc) the list in the picture is being rebuilt. The Listener is actually redrawing the widget without a change in the Bloc State it's listening to. I can't get my head around why it is happening. Does anyone have a clue?

I found this link discussing the issue, but I got nothing useful out of it.

Answer 1

For anyone looking at this now, you can call buildWhen after building Builder to provide some condition when to build.

From docs:

An optional [buildWhen] can be implemented for more granular control over how often [BlocBuilder] rebuilds. [buildWhen] will be invoked on each [cubit] state change. [buildWhen] takes the previous state and current state and must return a [bool] which determines whether or not the [builder] function will be invoked. The previous state will be initialized to the state of the [cubit] when the [BlocBuilder] is initialized. [buildWhen] is optional and if omitted, it will default to true .

Example:

    return Scaffold(
  appBar: AppBar(
    title: BlocBuilder<Bloc, State>(
      buildWhen: (p, c) => p.isEditing != c.isEditing,
      builder: (context, state) {
        return Text(state.isEditing ? 'Edit' : 'Create');
      },
    ),