如何从存储库返回 LiveData [英] How to Return LiveData from Repository

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.

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

1. 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
    }
}

这篇关于如何从存储库返回 LiveData的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！