如何从存储库返回 LiveData

本文介绍了如何从存储库返回 LiveData的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我只是看不到如何将 LiveData 从 Repo 链接到 VM，所以我尝试将其归结为最简单的示例！:

I just can't see how to chain LiveData from Repo to VM, so I have tried to boil this down to the most simple of example!:

片段

class LoginFragment : Fragment() { private lateinit var loginViewModel: LoginViewModel private var mCurrentName = "Blank!" override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { // Inflate the layout for this fragment val binding: LoginFragmentBinding = DataBindingUtil.inflate( inflater, R.layout.login_fragment, container, false) binding.apply { loginButton.setOnClickListener{ loginViewModel.changeText() } } return binding.root } override fun onActivityCreated(savedInstanceState: Bundle?) { super.onActivityCreated(savedInstanceState) loginViewModel = ViewModelProviders.of(this).get(LoginViewModel::class.java) loginViewModel.getCurrentName().observe(viewLifecycleOwner, Observer { mCurrentName = it // I'm expecting mCurrentName to equal "Button Clicked!" when button clicked.. makeToast() // Toast works, but variable remains unchanged.. }) } private fun makeToast() { Toast.makeText(activity, mCurrentName, Toast.LENGTH_LONG).show() }

视图模型

class LoginViewModel : ViewModel() { private val firestoreRepository : FirestoreRepository = FirestoreRepository() private var mCurrentName = MutableLiveData<String>() fun changeText(){ mCurrentName = firestoreRepository.changeText() }

存储库

class FirestoreRepository { private val mCurrentName = MutableLiveData<String>() fun changeText(): MutableLiveData<String> { mCurrentName.value = "Button Clicked!!" return mCurrentName }

我假设我误解了观察者函数的工作原理..

I'm assuming I have misunderstood how the observer function works..

推荐答案

其实如果你在repository中维护LiveData，我认为不需要单独的LiveData 在 ViewModel 中也是如此.您只需要从活动中观察一次 LiveData.然后直接对存储库实例进行任何更改.所以如果我必须在你的代码中展示它，它可能看起来像这样.

Actually If you are maintaining LiveData in repository, I don't think there's a need of separate LiveData in ViewModel as well. You just have to observe the LiveData once from the activity. Then make any changes to repository instance directly. So If I have to show it in your code, It might look something like this.

Activity 类:将 makeToast 方法更改为observeCurrentName()，如下所示:

Activity class: Change makeToast method to observeCurrentName() like this: private fun observeCurrentName() { vm.getCurrentName().observe(this, Observer{ //Toast here }) }

你的虚拟机:

Your VM:

class LoginViewModel : ViewModel() { ... fun getCurrentName(): MutableLiveData<String>{ return repository.getCurrentName() } fun setCurrentName(name: String?){ repository.setCurrentName(name) } ... }

您的存储库:

Your repository:

class FirestoreRepository { private val mCurrentName = MutableLiveData<String>() fun getCurrentName(): MutableLiveData<String>{ return mCurrentName } fun setCurrentName(name: String?){ mCurrentName.value = name //This will trigger observer in Activity } }