android - 如何使用 ViewModel 和 Databinding 实现验证？

Question

使用 ViewModel 和数据绑定(bind)验证表单数据的最佳方法是什么？

我有一个简单的注册 Activity ，它链接绑定(bind)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 {

        }
    }
}

ViewModel 带有 4 个 ObservableFields 和 signUp() 方法，应该在向服务器提交数据之前验证数据。

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!!)
    }
}

我想我们可以为每个输入添加四个 bool ObservableFields，在 signUp() 中我们可以检查输入并更改 bool ObservableField 的状态，这将在布局上产生出现错误

val isNameError: ObservableField<Boolean> = ObservableField()


fun signUp() {

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

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

但我不确定 ViewModel 是否应该负责验证并向用户显示错误，我们会有样板代码

<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

有很多方法可以实现这一点。我告诉你两个解决方案，都很好，你可以使用你认为适合你的。

我使用 extends BaseObservable 因为我发现这比将所有字段转换为 Observers 容易。你也可以使用 ObservableFields。

方案一(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}"/>

Model.java

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

你也可以替换

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

与

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

因为 android:afterTextChanged 和 passwordValidator 的参数相同。