如何使用导航架构组件从片段中获取结果?

问题描述

假设我们有两个片段:MainFragment 和 SelectionFragment.第二个是用于选择某个对象的构建，例如一个整数.从第二个片段接收结果有不同的方法，如回调、总线等.

Let's say that we have two fragments: MainFragment and SelectionFragment. The second one is build for selecting some object, e.g. an integer. There are different approaches in receiving result from this second fragment like callbacks, buses etc.

现在，如果我们决定使用导航架构组件来导航到第二个片段，我们可以使用以下代码:

Now, if we decide to use Navigation Architecture Component in order to navigate to second fragment we can use this code:

NavHostFragment.findNavController(this).navigate(R.id.action_selection, bundle)

其中 bundle 是 Bundle 的一个实例(当然).如您所见，我们无法访问 SelectionFragment，我们可以在其中放置回调.问题是，如何使用导航架构组件接收结果?

where bundle is an instance of Bundle (of course). As you can see there is no access to SelectionFragment where we could put a callback. The question is, how to receive a result with Navigation Architecture Component?

推荐答案

他们添加了一个 修复 在 2.3.0-alpha02 版本中.

They have added a fix for this in the 2.3.0-alpha02 release.

如果从 Fragment A 导航到 Fragment B 并且 A 需要 B 的结果:

If navigating from Fragment A to Fragment B and A needs a result from B:

findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<Type>("key")?.observe(viewLifecycleOwner) {result ->
    // Do something with the result.
}

如果在Fragment B并且需要设置结果:

If on Fragment B and need to set the result:

findNavController().previousBackStackEntry?.savedStateHandle?.set("key", result)

我最终为此创建了两个扩展:

I ended up creating two extensions for this:

fun Fragment.getNavigationResult(key: String = "result") =
    findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<String>(key)

fun Fragment.setNavigationResult(result: String, key: String = "result") {
    findNavController().previousBackStackEntry?.savedStateHandle?.set(key, result)
}

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