将一个LiveData观察到另一个LiveData Observr中 [英] Observe one LiveData into other LiveData Observr

问题描述

我有两个LiveData:

1. MutableLiveData<Int>-用户可以通过点击"+"和-"按钮来选择数字.

1. MutableLiveData<Int> -User could choose number by taping at "+" and "-" buttton.

LiveData>-这是我通过调用方法getLessonsForThatDay(number:Int)从RoomData库获得的数据.

LiveData> - it's my data from RoomData base by call method getLessonsForThatDay(number:Int).

我必须使用该MutableLiveData值更新我的方法getLessonForThatDay(value).

I have to update my method getLessonForThatDay(value) with that MutableLiveData value.

我尝试使用MediatorLiveData<>，但我不明白.

I've tried to use MediatorLiveData<> but i don't get it.

viewModel.dayOfWeek.observe(viewLifecycleOwner, androidx.lifecycle.Observer { dayOfWeekValue ->
        d("$dayOfWeekValue")
        viewModel.getLessonsForThatDay(dayOfWeekValue).observe(viewLifecycleOwner, androidx.lifecycle.Observer { lessons ->
            adapter.updateData(lessons)
            subjectsListTimetableRecyclerView.layoutManager = LinearLayoutManager(context)
            subjectsListTimetableRecyclerView.adapter = adapter
        })
    })

• 列表项

推荐答案

首先在viewmodel中定义这样的liveData.

private val dayOfWeekChangRequest = MutableLiveData<Int>()

和类似的方法，单击+时，单击该方法.

and a method like this, when + , - clicked, call this method.

fun dayOfWeekChanged(dayOfWeek: Int) {

    dayOfWeekChangRequest.value = dayOfWeek
}

现在为lessonsOfThatDay

val lessonsForThatDay: LiveData<List<Lesson>> = Transformations
        .switchMap(dayOfWeekChangRequest) { day ->
            yourDataBaseRepository.getLessonsOfThatDay(day)
        }

通过此转换，每次更改dayOfWeek时，lessonsForThatDay值都会更改.

with this transformation, every time you change your dayOfWeek, the lessonsForThatDay value will be changed.

最后在活动中观察

viewModel.lessonsForThatDay.observe(viewLifecycleOwner, Observer { 
        lessons ->
        adapter.updateData(lessons)
        subjectsListTimetableRecyclerView.layoutManager = LinearLayoutManager(context)
        subjectsListTimetableRecyclerView.adapter = adapter
    })

这篇关于将一个LiveData观察到另一个LiveData Observr中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！