我的MediatorLiveData没有更新

Question

我不知道为什么我的mediatorLiveData不更新？我还在我的活动文件中设置了观察者。我想做的是

单击将向mediatorLivedata

• another按钮添加源数据的

1. 按钮，该按钮将不断更改livedata，以便我的中介livedata应该更新( changeLiveData1是此处的按钮)

我是按顺序做的，似乎不起作用。此外，我在构造调用期间初始化了我的第一点。同样的问题..。MainActivity.kt

class MainActivity : AppCompatActivity() {

    lateinit var viewModel: MainViewModel

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

        viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)

        viewModel.mediatorLiveData.observe(this, Observer {

            text_view_content.text = it
        })

        livedata1.setOnClickListener {

            viewModel.changeLiveData1()
        }

        livedata2.setOnClickListener {
            viewModel.changeLiveData2()
        }

        add_source.setOnClickListener {
            viewModel.addSourceLivedata1()
        }
    }
}

MainViewModel.kt类MainViewModel : ViewModel() {

val mediatorLiveData: MediatorLiveData<String>
    get() = MediatorLiveData()


val _livedata1: MutableLiveData<String>
    get() = MutableLiveData<String>()


var change = 0
fun changeLiveData1() {
    change++
    _livedata1.value = "chnaged lived data...$change"
}

fun changeLiveData2() {

}


fun addSourceLivedata1() {

    var count = 0
    mediatorLiveData.addSource(_livedata1) {
        count++
        Log.d("MainView", "$count is ")
        if (count > 5) {
            mediatorLiveData.value = "changed from adding source... $count"
        } else {
            mediatorLiveData.value = "count is less than 5"
            Log.d("MainView", "count is $count")
        }
    }

}
}

Answer 1

每次访问变量时都要创建一个新实例。

val mediatorLiveData: MediatorLiveData<String>
    get() = MediatorLiveData()

val _livedata1: MutableLiveData<String>
    get() = MutableLiveData<String>()

把它改成

val mediatorLiveData: MediatorLiveData<String> = MediatorLiveData()

val _livedata1: MutableLiveData<String> = MutableLiveData<String>()