Android：ViewModel“可计算观察到”

Question

您是否可以在Android中计算出可观测值（例如可以在VueJS中进行计算）？

class MainActivityViewModel() : ViewModel() {
    val speedInput = MutableLiveData<Double>() // Actual value from sensor input.
    val speedFactor = MutableLiveData<Double>() // To be set from shared preferences

    val speed = speedInput * speedFactor // The value we need is computed from two observables.
}

Answer 1

如果需要将多个LiveData合并为一个，则有一个MediatorLiveData。它可以将多个LiveData用作源，并根据这些源“计算”自己的值（因此，也应该观察它的值）。

类似这样的东西：

.........
val speed = MediatorLiveData<Double>()

speed.addSource(speedInput) { value ->
    speed.value = computeSpeed(speedInput, speedFactor)
}
speed.addSource(speedFactor) { value ->
    speed.value = computeSpeed(speedInput, speedFactor)
}
.........

fun computeSpeed(speedInput: MutableliveData<Double>, speedFactor: MutableliveData<Double>) = speedInput.value * speedFactor.value