MediatorLiveData直接从ViewModel绑定到视图

Question

当4个EditTexts有超过X个字符且电子邮件是有效的时，我试图启用/禁用一个按钮(忽略xml，仍然应用样式)：

  <Button
            android:id="@+id/fragment_login_button"
            android:fontFamily="@font/montserrat_regular"
            android:layout_marginTop="20dp"
            android:textColor="@android:color/white"
            android:background="@drawable/button_primary"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:enabled="@{viewModel.createAccountDetailsValid}"
            android:layout_marginRight="20dp"
            android:text="create account "
            android:onClick="@{(theView) -> handler.onCreateClick(theView, viewModel)}"
            app:layout_constraintTop_toBottomOf="@id/fragment_login_companyText"
    />

我让它使用MediatorLiveData和按钮所依赖的4 MutableLiveData来工作，但是我发现通过这样做可以使违背MVVM标准，但这是唯一的工作方式，因为MediatorLiveData只允许addSource (如果至少有一个观察者)，请查看代码：

关于我的观点模型：

//USER DATA
val email: MutableLiveData<String> = MutableLiveData()
val name: MutableLiveData<String> = MutableLiveData()
val surname: MutableLiveData<String> = MutableLiveData()
val company: MutableLiveData<String> = MutableLiveData()
val createAccountDetailsValid: MediatorLiveData<Boolean> = MediatorLiveData()

fun populateMediator(owner: LifecycleOwner) {
        createAccountDetailsValid.observe(owner, Observer {  })
        createAccountDetailsValid.addSource(email) {
            createAccountDetailsValid.value = isCreateAccountDetailsValid()
        }
        createAccountDetailsValid.addSource(name) {
            createAccountDetailsValid.value = isCreateAccountDetailsValid()
        }
        createAccountDetailsValid.addSource(surname) {
            createAccountDetailsValid.value = isCreateAccountDetailsValid()
        }
        createAccountDetailsValid.addSource(company) {
            createAccountDetailsValid.value = isCreateAccountDetailsValid()
        }
    }

private fun isCreateAccountDetailsValid() : Boolean {
    if(email.value == null || name.value == null || surname.value == null || company.value == null) return false
    return android.util.Patterns.EMAIL_ADDRESS.matcher(email?.value!!).matches() && name.value?.length!! >= 3 && surname.value?.length!! >= 3 && company.value?.length!! >= 3
}

在我的碎片上：

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    binding = DataBindingUtil.inflate(inflater, R.layout.fragment_login, container,false)
    viewModel = ViewModelProviders.of(this, viewModelFactory).get(LoginViewModel::class.java)
    binding.viewModel = viewModel
    binding.handler = LoginHandler()
    binding.setLifecycleOwner(this)
    viewModel.setLifecycleOwner(this as LifecycleOwner)
    return binding.root
}

就像我说的那样，ViewModel对视图( LifecycleOwner )有一个引用，是的，我可以将空的观察者放在片段上，不需要将LifecycleOwner传递给ViewModel，但仍然感觉不太好，也许我在这里有点完美主义，但我敢打赌还有另一种方式可以直接从ViewModel绑定，而不必在片段中设置isEnable来观察MediatorLiveData？

谢谢!

Answer 1

有黑带的评论，我应该做错了什么，结果是复杂和解决问题，同时试图使它发挥作用。

他说过，数据绑定观察到了，您可以像我一样在addSource init上使用viewModel init，并使其正常工作：

 val createAccountResult: MutableLiveData<Resource<Void>> = MutableLiveData()
val loginResult: MutableLiveData<Resource<Void>> = MutableLiveData()

//USER DATA
val email: MutableLiveData<String> = MutableLiveData()
val name: MutableLiveData<String> = MutableLiveData()
val surname: MutableLiveData<String> = MutableLiveData()
val company: MutableLiveData<String> = MutableLiveData()

var createAccountDetailsValid: MediatorLiveData<Boolean> = MediatorLiveData()

init {
    createAccountDetailsValid.addSource(email) {
        createAccountDetailsValid.value = isCreateAccountDetailsValid()
    }
    createAccountDetailsValid.addSource(name) {
        createAccountDetailsValid.value = isCreateAccountDetailsValid()
    }
    createAccountDetailsValid.addSource(surname) {
        createAccountDetailsValid.value = isCreateAccountDetailsValid()
    }
    createAccountDetailsValid.addSource(company) {
        createAccountDetailsValid.value = isCreateAccountDetailsValid()
    }
}

谢谢你的帮助@黑带