如何在Flutter中创建服务/提供程序？

Question

Let's say I need a user service which has all my user variables and functions, and another item service with all item variables and functions, etc etc. I want all this data and functions available throughout the project, passing the user data where it's needed, for example.

I suspect it has something to do with inherited widgets, but how does that work? Like, I see how I could use one inherited widget at the root level, but am I supposed to build a bunch of inherited widgets at the root-level for each service? Or just put ALL the data in the one top inherited widget? Seems like that may get messy. I have yet to see an example of this.

... or should I just be using a class with static variables and call on that where I need it?

Answer 1

请参阅上面的Günter提供的链接。如果您有三十分钟的时间观看Brian Egan的DartConf 18演示文稿，请保持简洁，状态。还看到Brian的示例代码在这里。他展示了使用InheritedWidget和Controller以及Flutter Redux编码的相同应用。

这是来自我的一个简单应用程序的单个InheritedWidget的示例...

class StateContainer extends InheritedWidget {
  final List<Membership> memberships;

  final IntFunction getNextIndex;
  final VoidMembershipFunction updateMembership;
  final VoidIntFunction deleteMembership;

  const StateContainer({
    this.memberships,
    this.getNextIndex,
    this.updateMembership,
    this.deleteMembership,
    Widget child,
  })
      : super(child: child);

  static StateContainer of(BuildContext context) {
    return context.inheritFromWidgetOfExactType(StateContainer);
  }

  @override
  bool updateShouldNotify(StateContainer oldWidget) {
    return true;
  }
}

我作为孩子传入了我的MaterialApp。然后，如果StateContainer可以访问数据和方法，则很大一部分树将变为无状态。您可以将它们视为模型和控制器合二为一。树中的构建方法通常以...开始

  @override
  Widget build(BuildContext context) {
    final StateContainer container = StateContainer.of(context);

来访问他们。

没错，单个InheritedWidget很快就会变得笨拙-您可以在其中投资探索Redux-请参阅讲座的最后10分钟。以我的经验，最混乱的地方是在比较所有成员变量时的updateShouldNotify方法。（在这个简单的示例中，只有一个成员变量，并且setState仅在其更改时才被调用，因此它总是很小。）