问题

让我们假设我有一个 `Person` 接口，其中有一个 `name` 可观察对象：

```java
interface Person {
  Observable<String> name;
}

然后是它的实现：

class David implements Person {
  Observable<String> name = BehaviorSubject.createDefault("David");
}

现在有一个问题，因为我无法获取 name 可观察对象的当前值：

class Main {
  public static void main(String[] args) {
    Person person = PersonFactory.create();
    System.out.println(??person.name.currentValue??);
  }
}

我不想在我的接口中将名称公开为 BehaviorSubject，因为那样每个人都可以更改名称，这不是我想要的。

我在某种程度上理解可观察对象的逻辑，所以我知道它们不被设计用于存储任何值。那么在 RxJava 中，“带有当前值的不可变可观察对象” 是什么？

在 Android 中有 LiveData 和 MutableLiveData。据我理解，MutableLiveData 相当于 BehaviorSubject，那么在 RxJava 中相当于 LiveData 的是什么？

<details>
<summary>英文:</summary>

Let&#39;s say I have an `Person` interface, that have an `name` observable:

interface Person {
Observable<String> name;
}

And it's implementation:
```java
class David implements Person {
  Observable<String> name = BehaviorSubject<>.createDefault("David");
}

And now there is a problem, because I can't get current value of name observable:

class Main {
  public static void main(String[] args) {
    Person person = PersonFactory.create();
    System.out.println(??person.name.currentValue??);
  }
}

I don't want to expose the name as BehaviorSubject in my interface, because then everyone would be able to change the name, which isn't what I want.

I kind of understand a logic of Observables, so I know they aren't designed to store any value. So what is "an immutable observable with current value" in RxJava?

In Android there is a LiveData and MutableLiveData. To my understanding MutableLiveData is the equivalent of BehaviorSubject, so what is the equivalent of LiveData in RxJava?

答案1

得分: 1

定义变量name的类型为内部主题，主题内部为David，并使用hide()方法将其公开为可观察对象。使用hide将确保外部世界无法调用onNext，即无法改变名称。在这里查看hide()的文档

class David implements Person {

    private PublishSubject<String> nameSubject = BehaviorSubject.createDefault("David");

    public Observable<String> observeName() {
        return nameSubject.hide();
    }

    // 如果希望外部世界更新名称
    public void setName(String name) {
        nameSubject.onNext(name);
    }
}

class David implements Person {
  
    private PublishSubject<String> nameSubject = BehaviorSubject<>.createDefault("David");

    public Observable<String> observeName() {
        return nameSubject.hide();
    }

    // If you want the outside world to update the name
    public void setName(String name) {
        nameSubject.onNext(name)
    }
}

答案2

得分: 0

我决定创建自己的`LiveData`，使用字段委托

interface LiveData<out T> {
    val observable: Observable<out T>
    val value: T

    fun subscribe(onNext: Consumer<in T>): Disposable = observable.subscribe(onNext)
}

class MutableLiveData<T>(initial: T) : LiveData<T> {
    private val subject: BehaviorSubject<T> = BehaviorSubject.createDefault(initial)

    override val observable: Observable<out T> = subject

    override var value: T
        get() = subject.value
        set(value) = subject.onNext(value)

    fun mutate(mutationFunction: T.() -> Unit) {
        value.mutationFunction()
        value = value
    }
}

interface LiveData<out T> {
    val observable: Observable<out T>
    val value: T

    fun subscribe(onNext: Consumer<in T>): Disposable = observable.subscribe(onNext)
}

class MutableLiveData<T>(initial: T) : LiveData<T> {
    private val subject: BehaviorSubject<T> = BehaviorSubject.createDefault(initial)

    override val observable: Observable<out T> = subject

    override var value: T
        get() = subject.value
        set(value) = subject.onNext(value)

    fun mutate(mutationFunction: T.() -> Unit) {
        value.mutationFunction()
        value = value
    }
}