Rxjava + MVVM + databinding

MainActivity

public class MainActivity extends BaseActivity {

    @NonNull
    @Override
    protected ViewModel createViewModel() {
        return new MainViewModel(getNavigator());
    }

    @Override
    protected int getLayoutId() {
        return R.layout.activity_main;
    }
}

BaseActivity

public abstract class BaseActivity extends MvvmActivity {

    @NonNull
    protected Navigator getNavigator() {
        return new Navigator() {
            @Override
            public void openDetailsPage(Item item) {
                navigate(ItemDetailsActivity.class);
            }

            @Override
            public void navigateToFunctionalDemo() {
                navigate(DataLoadingActivity.class);
            }

            @Override
            public void navigateToAdapterDemo() {
                navigate(ItemListActivity.class);
            }

            @Override
            public void navigateToTwoWayBindingDemo() {
                navigate(SearchActivity.class);
            }

            @Override
            public void navigateToCalculatorDemo() {
                navigate(CalculatorActivity.class);
            }

            private void navigate(Class<?> destination) { // 화면 이동 
                Intent intent = new Intent(BaseActivity.this, destination);
                startActivity(intent);
            }
        };
    }

    @NonNull
    protected MessageHelper getMessageHelper() {
        return new MessageHelper() {
            @Override
            public void show(String message) {
                Toast.makeText(BaseActivity.this, message, Toast.LENGTH_SHORT).show();
            }
        };
    }

}

MessageHelper 인터페이스

public interface MessageHelper {
    void show(String message);
}

MvvmActivity

public abstract class MvvmActivity extends AppCompatActivity {
    private ViewDataBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, getLayoutId());
        getDefaultBinder().bind(binding, createViewModel());
    }

    @Override
    protected void onDestroy() {
        getDefaultBinder().bind(binding, null);
        binding.executePendingBindings();
        super.onDestroy();
    }

    @NonNull
    private ViewModelBinder getDefaultBinder() {
        ViewModelBinder defaultBinder = BindingUtils.getDefaultBinder();
        Preconditions.checkNotNull(defaultBinder, "Default Binder");
        return defaultBinder;
    }

    @NonNull
    protected abstract ViewModel createViewModel();

    @LayoutRes
    protected abstract int getLayoutId();
}

ViewModelBinder 인터페이스

public interface ViewModelBinder {
    void bind(ViewDataBinding viewDataBinding, ViewModel viewModel);
}

Preconditions 클래스

public class Preconditions {
    public static <T> void checkNotNull(T value, String name) {
        if (value == null) {
            throw new NullPointerException(name + " should not be null");
        }
    }
}

ExampleApplication ( 기본 애플리케이션 )

public class ExampleApplication extends Application {
    public static RefWatcher getRefWatcher(Context context) {
        ExampleApplication application = (ExampleApplication) context.getApplicationContext();
        return application.refWatcher;
    }

    private RefWatcher refWatcher;

    @Override
    public void onCreate() {
        super.onCreate();
        refWatcher = LeakCanary.install(this);
        BindingUtils.setDefaultBinder(BindingAdapters.defaultBinder);
    }
}

CalculatorActivity 로 이동했어

public class CalculatorActivity extends MvvmActivity {

    @NonNull
    @Override
    protected ViewModel createViewModel() {
        return new CalculatorViewModel();
    }

    @Override
    protected int getLayoutId() {
        return R.layout.activity_calculator;
    }
}

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

        <variable
            name="vm"
            type="com.manaschaudhari.android_mvvm.sample.calculator_example.CalculatorViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        tools:context="com.manaschaudhari.android_mvvm.sample.calculator_example.CalculatorActivity">

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="Number 1"
            android:inputType="number"
            android:text="@={vm.number1}" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="Number 2"
            android:inputType="number"
            android:text="@={vm.number2}" />

        <RadioGroup
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checkedButton="@={vm.operation}">

            <RadioButton
                android:id="@+id/radio_add"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="+" />

            <RadioButton
                android:id="@+id/radio_subtract"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="-" />

            <RadioButton
                android:id="@+id/radio_multiply"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="*" />

            <RadioButton
                android:id="@+id/radio_divide"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="/" />
        </RadioGroup>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{vm.result}" />
    </LinearLayout>

</layout>

CalculatorViewModel 에서 처리

public class CalculatorViewModel implements ViewModel {

    public final ObservableField<String> number1 = new ObservableField<>("");
    public final ObservableField<String> number2 = new ObservableField<>("");
    public final ObservableField<Calculator.Operation> operation = new ObservableField<>(Calculator.Operation.ADD);

    public final ReadOnlyField<String> result;

    public CalculatorViewModel() {
        final Calculator calculator = new Calculator();

        Observable<String> result = Observable.combineLatest(
                toObservable(number1), toObservable(number2), toObservable(operation),
                new Function3<String, String, Calculator.Operation, String>() {
                    @Override
                    public String apply(String s1, String s2, Calculator.Operation operation) throws Exception {
                        try {
                            int n1 = Integer.parseInt(s1);
                            int n2 = Integer.parseInt(s2);

                            Integer result = calculator.run(n1, n2, operation);
                            return (result != null) ? result.toString() : "ERROR";

                        } catch (NumberFormatException e) {
                            return "";
                        }
                    }
                });
        this.result = toField(result);
    }
}

Calculator 클래스

public class Calculator {

    @Nullable
    public Integer run(int a, int b, @NonNull Operation operation) {
        switch (operation) {
            case ADD:
                return a + b;
            case SUBTRACT:
                return a - b;
            case MULTIPLY:
                return a * b;
            case DIVIDE:
                if (b != 0) {
                    return a / b;
                } else {
                    return null;
                }
        }
        return null;
    }

    public enum Operation {
        ADD, SUBTRACT, MULTIPLY, DIVIDE
    }
}

이렇게 하는 이유...

Rxjava : 일단 옵저버 패턴, 관측하고 있다가 변경사항이 있을 때 자동으로 메소드가 호출되는 방식(이 경우에는 run)

Mvvm : 클래스간의 종속성을 최소화 하고 (자바의 특징인 객체생성 및 사용) 모듈테스트가 편하다는 점인데

C#.NET 의 특징이긴하다. 근데 진짜 좋은지를 피부로 못느끼겠음.

한마디로 이런 방식은 안드로이드자바를 C#.NET의 WPF MVVM 패턴화 시킨 것

C#이 더 좋다는 뜻인데.