如何使用Android导航而不绑定到ViewModel(MVVM)中的UI? [英] How to use android navigation without binding to UI in ViewModel (MVVM)?
问题描述
我正在使用Google I/O 2018上展示的android导航，似乎可以通过绑定到某些视图或使用NavHost从Fragment获取它来使用它.但是我需要根据几个条件从我的第一个片段从ViewModel导航到另一个特定的视图.对于ViewModel，我扩展了AndroidViewModel，但是我不明白下一步该怎么做.我不能将getApplication强制转换为片段/活动"，也不能使用NavHostFragment.另外，我不能仅将导航绑定到onClickListener，因为startFragment仅包含一个ImageView.如何从ViewModel导航?
I am using android navigation that was presented at Google I/O 2018 and it seems like I can use it by binding to some view or by using NavHost to get it from Fragment. But what I need is to navigate to another specific view from ViewModel from my first fragment depending on several conditions. For ViewModel, I extend AndroidViewModel, but I cannot understand how to do next. I cannot cast getApplication to Fragment/Activity and I can't use NavHostFragment. Also I cannot just bind navigation to onClickListener because the startFragment contains only one ImageView. How can I navigate from ViewModel?
class CaptionViewModel(app: Application) : AndroidViewModel(app) {
private val dealerProfile = DealerProfile(getApplication())
val TAG = "REGDEB"
fun start(){
if(dealerProfile.getOperatorId().isEmpty()){
if(dealerProfile.isFirstTimeLaunch()){
Log.d(TAG, "First Time Launch")
showTour()
}else{
showCodeFragment()
Log.d(TAG, "Show Code Fragment")
}
}
}
private fun showCodeFragment(){
//??
}
private fun showTour(){
//??
}
}
我的片段
class CaptionFragment : Fragment() {
private lateinit var viewModel: CaptionViewModel
private val navController by lazy { NavHostFragment.findNavController(this) }
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
viewModel = ViewModelProviders.of(this).get(CaptionViewModel::class.java)
return inflater.inflate(R.layout.fragment_caption, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel.start()
}
}
我想在ViewModel中保留导航逻辑
I want to keep logic of navigation in ViewModel
推荐答案
如何从ViewModel导航?
How can I navigate from ViewModel?
答案是请不要. ViewModel旨在存储和管理与UI相关的数据.
The answer is please don't. ViewModel is designed to store and manage UI-related data.
新答案
在我以前的回答中，我说过我们不应该从ViewModel导航，原因是因为要导航，ViewModel必须具有对Activity/Fragments的引用，我相信(可能不是最好的，但我仍然相信它) )绝不是一个好主意.
In my previous answers, I said that we shouldn't navigate from ViewModel, and the reason is because to navigate, ViewModel must have references to Activities/Fragments, which I believe (maybe not the best, but still I believe it) is never a good idea.
但是，在Google推荐的应用程序体系结构中，它提到我们应从模型驱动UI .在我认为之后，这意味着什么?
But, in recommended app architecture from Google, it mentions that we should drive UI from model. And after I think, what do they mean with this?
因此，我检查了"android-architecture"中的示例，并发现了Google如何做到这一点的有趣方式.
So I check a sample from "android-architecture", and I found some interesting way how Google did it.
请在此处检查: todo-mvvm-databinding
事实证明，他们确实从模型驱动用户界面.但是如何?
As it turns out, they indeed drive UI from model. But how?
- They created an interface TasksNavigator that basically just a navigation interface.
- Then in the TasksViewModel, they have this reference to TaskNavigator so they can drive UI without having reference to Activities / Fragments directly.
- Finally, TasksActivity implemented TasksNavigator to provide detail on each navigation action, and then set navigator to TasksViewModel.
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