如何使用ViewModel和Databinding实现验证？

Question

使用ViewModel和Databinding验证表单数据的最佳方法是什么？

我有一个简单的Sign-Up活动，该活动链接绑定布局和ViewModel

class StartActivity : AppCompatActivity() {

    private lateinit var binding: StartActivityBinding
    private lateinit var viewModel: SignUpViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        viewModel = ViewModelProviders.of(this, SignUpViewModelFactory(AuthFirebase()))
                .get(SignUpViewModel::class.java);

        binding = DataBindingUtil.setContentView(this, R.layout.start_activity)
        binding.viewModel = viewModel;

        signUpButton.setOnClickListener {

        }
    }
}

ViewModel4 ObservableFields和signUp()在向服务器提交数据之前应该验证数据的方法。

class SignUpViewModel(val auth: Auth) : ViewModel() {
    val name: MutableLiveData<String> = MutableLiveData()
    val email: MutableLiveData<String> = MutableLiveData()
    val password: MutableLiveData<String> = MutableLiveData()
    val passwordConfirm: MutableLiveData<String> = MutableLiveData()

    fun signUp() {

        auth.createUser(email.value!!, password.value!!)
    }
}

我猜我们可以为每个输入添加四个boolean ObservableField，然后signUp()我们可以检查输入并更改boolean ObservableField的状态，这会在布局上产生错误

val isNameError: ObservableField<Boolean> = ObservableField()


fun signUp() {

        if (name.value == null || name.value!!.length < 2 ) {
            isNameError.set(true)
        }

        auth.createUser(email.value!!, password.value!!)
    }

但是我不确定ViewModel应该负责验证并向用户显示错误，我们将提供样板代码

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>

        <import type="android.view.View" />

        <variable
            name="viewModel"
            type="com.maximdrobonoh.fitnessx.SignUpViewModel" />
    </data>

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorGreyDark"
        android:orientation="vertical"
        android:padding="24dp">

        <TextView
            android:id="@+id/appTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:text="@string/app_title"
            android:textColor="@color/colorWhite"
            android:textSize="12sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <LinearLayout
            android:id="@+id/screenTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:orientation="horizontal"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/appTitle">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginEnd="4dp"
                android:text="@string/sign"
                android:textColor="@color/colorWhite"
                android:textSize="26sp"
                android:textStyle="bold" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/up"
                android:textColor="@color/colorWhite"
                android:textSize="26sp" />
        </LinearLayout>

        <LinearLayout
            android:id="@+id/form"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="24dp"
            android:orientation="vertical"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/screenTitle">

            <android.support.v7.widget.AppCompatEditText
                style="@style/SignUp.InputBox"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/sign_up_name"
                android:inputType="textPersonName"
                android:text="@={viewModel.name}" />

            <android.support.v7.widget.AppCompatEditText
                style="@style/SignUp.InputBox"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/sign_up_email"
                android:inputType="textEmailAddress"
                android:text="@={viewModel.email}"
               />

            <android.support.v7.widget.AppCompatEditText
                style="@style/SignUp.InputBox"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/sign_up_password"
                android:inputType="textPassword"
                android:text="@={viewModel.password}" />

            <android.support.v7.widget.AppCompatEditText
                style="@style/SignUp.InputBox"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/sign_up_confirm_password"
                android:inputType="textPassword"
                android:text="@={viewModel.passwordConfirm}" />

            <Button
                android:id="@+id/signUpButton"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="16dp"
                android:background="@drawable/button_gradient"
                android:text="@string/sign_up_next_btn"
                android:textAllCaps="true"
                android:textColor="@color/colorBlack" />

        </LinearLayout>

    </android.support.constraint.ConstraintLayout>
</layout>

Answer 1

这种方法使用 TextInputLayouts，一个自定义绑定适配器，并为表单错误创建一个枚举。我认为结果在 xml 中读取得很好，并将所有验证逻辑保留在 ViewModel 中。

视图模型：

class SignUpViewModel() : ViewModel() {

   val name: MutableLiveData<String> = MutableLiveData()
   // the rest of your fields as normal

   val formErrors = ObservableArrayList<FormErrors>()

   fun isFormValid(): Boolean {
      formErrors.clear()
      if (name.value?.isNullOrEmpty()) {
          formErrors.add(FormErrors.MISSING_NAME)
      }
      // all the other validation you require
      return formErrors.isEmpty()
   }

   fun signUp() {
      auth.createUser(email.value!!, password.value!!)
   }

   enum class FormErrors {
      MISSING_NAME,
      INVALID_EMAIL,
      INVALID_PASSWORD,
      PASSWORDS_NOT_MATCHING,
   }

}

绑定适配器：

@BindingAdapter("app:errorText")
fun setErrorMessage(view: TextInputLayout, errorMessage: String) {
    view.error = errorMessage
}

XML：

<layout>

  <data>

        <import type="com.example.SignUpViewModel.FormErrors" />

        <variable
            name="viewModel"
            type="com.example.SignUpViewModel" />

  </data>

<!-- The rest of your layout file etc. -->

       <com.google.android.material.textfield.TextInputLayout
            android:id="@+id/text_input_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:errorText='@{viewModel.formErrors.contains(FormErrors.MISSING_NAME) ? "Required" : ""}'>

            <com.google.android.material.textfield.TextInputEditText
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="Name"
                android:text="@={viewModel.name}"/>

        </com.google.android.material.textfield.TextInputLayout>

<!-- Any other fields as above format -->

然后，可以从活动/片段调用 ViewModel，如下所示：

class YourActivity: AppCompatActivity() {

   val viewModel: SignUpViewModel
  // rest of class

  fun onFormSubmit() {
     if (viewModel.isFormValid()) {
        viewModel.signUp()
        // the rest of your logic to proceed to next screen etc.
     }
     // no need for else block if form invalid, as ViewModel, Observables
     // and databinding will take care of the UI
  }


}

Answer 2

有很多方法可以实现这一点。我告诉您两个解决方案，两个都很好，您可以使用适合自己的解决方案。

我extends BaseObservable之所以使用，是因为我发现将所有字段都转换为都比这容易Observers。您也可以使用ObservableFields。

解决方案1（使用自定义BindingAdapter）

在xml中

<variable
    name="model"
    type="sample.data.Model"/>

<EditText
    passwordValidator="@{model.password}"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@={model.password}"/>

模型

public class Model extends BaseObservable {
    private String password;

    @Bindable
    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
        notifyPropertyChanged(BR.password);
    }
}

DataBindingAdapter.java

public class DataBindingAdapter {
    @BindingAdapter("passwordValidator")
    public static void passwordValidator(EditText editText, String password) {
        // ignore infinite loops
        int minimumLength = 5;
        if (TextUtils.isEmpty(password)) {
            editText.setError(null);
            return;
        }
        if (editText.getText().toString().length() < minimumLength) {
            editText.setError("Password must be minimum " + minimumLength + " length");
        } else editText.setError(null);
    }
}

解决方案2（使用自定义afterTextChanged）

在xml中

<variable
    name="model"
    type="com.innovanathinklabs.sample.data.Model"/>

<variable
    name="handler"
    type="sample.activities.MainActivityHandler"/>

<EditText
    android:id="@+id/etPassword"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:afterTextChanged="@{(edible)->handler.passwordValidator(edible)}"
    android:text="@={model.password}"/>

MainActivityHandler.java

public class MainActivityHandler {
    ActivityMainBinding binding;

    public void setBinding(ActivityMainBinding binding) {
        this.binding = binding;
    }

    public void passwordValidator(Editable editable) {
        if (binding.etPassword == null) return;
        int minimumLength = 5;
        if (!TextUtils.isEmpty(editable.toString()) && editable.length() < minimumLength) {
            binding.etPassword.setError("Password must be minimum " + minimumLength + " length");
        } else {
            binding.etPassword.setError(null);
        }
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
    ActivityMainBinding binding;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.setModel(new Model());
        MainActivityHandler handler = new MainActivityHandler();
        handler.setBinding(binding);
        binding.setHandler(handler);
    }
}

更新资料

您也可以更换

android:afterTextChanged="@{(edible)->handler.passwordValidator(edible)}"

与

android:afterTextChanged="@{handler::passwordValidator}"

因为参数与android:afterTextChanged和相同passwordValidator。