MediatorLiveData 直接从 ViewModel 绑定到 View

Question

当 4 个 EditText 超过 X 个字符且电子邮件有效时，我正在尝试 enable/disable 一个按钮（忽略 xml，仍在应用样式）：

  <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"
    />

我将 MediatorLiveData 与按钮所依赖的 4 个 MutableLiveData 结合使用，但我发现我违反了 MVVM 标准 通过这样做，但这是唯一的工作方式，因为 MediatorLiveData 仅在至少有 1 个观察者的情况下才允许 addSource，请查看代码：

在我的视图模型上：

//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
}

在我的片段上：

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，它正在工作，但 ViewModel 有一个对 View (LifecycleOwner) 的引用，是的，我可以将空的观察者放在 Fragment 上，不需要将 LifecycleOwner 传递给 ViewModel，但仍然感觉不对，也许我在这里有点完美主义者，但我敢打赌还有另一种直接从 ViewModel 绑定的方法，而不必设置 isEnable 以观察 Fragment 中的 MediatorLiveData？

谢谢！

Answer 1

有 Blackbelt 评论我应该做错了什么，结果在试图让它工作时使问题复杂化并解决了问题。

他说数据绑定观察了吗，你可以像我一样在 viewModel init 上添加源并让它工作：

 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()
    }
}

感谢您的帮助@Blackbelt

MediatorLiveData 直接从 ViewModel 绑定到 View

MediatorLiveData binding directly from ViewModel to View

android

kotlin

android-databinding

android-livedata