Android开发：如何高效监听多个MutableLiveData属性的变化？

class testvm : viewmodel() {
    val isrequest = mutablelivedata<boolean>()
    val total = mutablelivedata<int>()
    val text = mediatorlivedata<string>()

    init {
        isrequest.value = false
        total.value = 10

        text.addsource(isrequest) { text.value = gettext() }
        text.addsource(total) { text.value = gettext() }
    }

    private fun gettext(): string {
        if (isrequest.value == true) {
            return "请求中"
        }
        val t = total.value ?: 0
        if (t >= 1000) {
            return "999+"
        }
        return t.tostring()
    }
}

//获取 ViewModel
val viewModel = ViewModelProvider(this).get(TestVM::class.java)

//观察 isRequest 的变化
viewModel.isRequest.observe(this) { isRequest ->
    updateButtonText()
}

//观察 total 的变化
viewModel.total.observe(this) { total ->
    updateButtonText()
}

private fun updateButtonText() {
    val text = viewModel.getText()
    myButton.text = text // myButton 是代表 Button 的变量
}