观察片段和活动中的 LiveData 实例

Question

我有一个简单的场景，我在片段中做一些事情，当我收到 LiveData 时，我想在 Activity 中做一些事情。

视图模型：

class MyViewModel(application: Application) : AndroidViewModel(application) {
    
   ...
    
    fun getUser(id: String): LiveData<User> {
        return repository.getUser(id)
    }
}

分段：

class MyFragment : Fragment() {

    private lateinit var myViewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        activity?.run {
            myViewModel = ViewModelProviders.of(this).get(MyViewModel::class.java)
        } ?: throw Exception("Invalid Activity")
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        button.setOnClickListener {
            showProgressBar()
            myViewModel.getUser(editText.text.toString()).observe(this, Observer { it ->
                //TODO
            })
        }
    }
}

活动：

class MainActivity : AppCompatActivity() {

    private lateinit var myViewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        myViewModel = ViewModelProviders.of(this).get(MyViewModel::class.java)
        //Here I would like to observe the user instance returned from the getUser() method
    }
}

所以我遇到的问题是我想要一个LiveData<User>in的实例，MyViewModel以便我可以在 Activity 和 Fragment 中观察它。我怎样才能做到这一点？

Answer 1

在片段中（作为最佳实践）应该使用

viewModel.userLiveData.observe(viewLifecycleOwner, Observer {
    //your code here
})

活动使用中

viewModel.userLiveData.observe(this, Observer {
        //your code here
    })

Answer 2

在 MyViewModel 类中创建

    val userLiveData =MutableLiveData<User>()

和吸气剂

    fun getUserLiveData(id: String): MutableLiveData<User> {
            return userLiveData
    }

    fun getUser(id: String){
    val disposableUser = repository.getUser(id)
    .subscribe({
        userLivedata.postValue(it)
    })

}

在活动或片段中称为

   myViewModel.getUserLiveData.observe(this, Observer { it ->
      //TODO
    })
   myViewModel.getUser(...)

现在在 ViewModel 中你有对象 User (userLiveData.getValue())