android - 流的乐趣，转换为实时数据时为空

Question

我正在尝试流程并尝试查看如何使用 Android View 模型将它们转换为 mvvm。这是我首先尝试测试的内容:

class HomeViewModel : ViewModel() {

    private lateinit var glucoseFlow: LiveData<Int>
    var _glucoseFlow = MutableLiveData<Int>()


    fun getGlucoseFlow() {
        glucoseFlow = flowOf(1,2).asLiveData()
        _glucoseFlow.value = glucoseFlow.value
    }
}


class HomeFragment : Fragment() {

    private lateinit var viewModel: HomeViewModel

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

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProviders.of(this).get(HomeViewModel::class.java)

        viewModel._glucoseFlow.observe(this, Observer {
            handleUpdate(it)
        })

        viewModel.getGlucoseFlow()
    }

    private fun handleUpdate(reading : Int) {
        glucose_reading.text = reading.toString()
    }
}

我的阅读数为空，但有什么想法吗？

Answer 1

发生这种情况是因为您试图分配 glucoseFlow.value至 _glucoseFlow.value直接，我想你应该使用 MediatorLiveData<Int> ，但这不是我的最终建议。

如果你收集流项，然后将它们分配给你的私有(private)变量，你就可以解决它。

// For private variables, prefer use underscore prefix, as well MutableLiveData for assignable values.
private val _glucoseFlow = MutableLiveData<Int>()
// For public variables, prefer use LiveData just to read values.
val glucoseFlow: LiveData<Int> get() = _glucoseFlow 

fun getGlucoseFlow() {
    viewModelScope.launch {
        flowOf(1, 2)
            .collect {
                _glucoseFlow.value = it
            }
    }
}

在 HomeViewModel 之前实现，开始观察你的公众glucoseFlow来自 HomeFragment并且您将能够接收非空序列值(1 和 2)。