问题

我在我的Android应用程序中更新刷新按钮状态时遇到了问题。在我的互动器中，我有一对主题来控制刷新按钮的状态。

class PageInteractor {
    private var isRefreshActionEnabled = false
    private val refreshStatePublisher by lazy {
        BehaviorSubject.create<Boolean>().apply {
            onNext(false)
        }
    }
    private var refreshActionPublisher: PublishSubject<Unit>? = null

    fun observeRefreshButtonState(): Observable<Boolean> {
        return refreshStatePublisher
    }

    fun observeRefreshAction(): Observable<Unit> {
        if (refreshActionPublisher?.hasComplete() == false && refreshActionPublisher?.hasObservers() == true) {
            refreshActionPublisher?.onComplete()
        }

        return PublishSubject.create<Unit>()
            .also {
                refreshActionPublisher = it
                updateRefreshButtonState()
            }
            .doOnDispose {
                updateRefreshButtonState()
            }
    }

    fun setRefreshActionEnabled(value: Boolean) {
        if (isRefreshActionEnabled != value) {
            isRefreshActionEnabled = value
            updateRefreshButtonState()
        }
    }

    fun onRefreshAction() {
        refreshActionPublisher?.onNext(Unit)
    }

    private fun updateRefreshButtonState() {
        refreshStatePublisher.onNext(refreshActionPublisher?.hasComplete() == false
            && refreshActionPublisher?.hasObservers() == true)
    }
}

我在我的Presenter中使用了这个互动器，它是一个Moxy presenter。

class PagePresenter(
        private val pageInteractor: PageInteractor
) : MvpPresenter<PageView> {
    override fun onFirstViewAttach() {
        super.onFirstViewAttach()

        pageInteractor
            .observeRefreshButtonState()
            .subscribe { isEnabled ->
                viewState.setRefreshButtonEnabled(isEnabled)
            }
            .addTo(disposable)
    }

    fun onRefreshButtonClicked() {
        pageInteractor.onRefreshAction()
    }
}

我的问题是，当我打开页面时，刷新按钮是禁用的。我进行了一些调试，似乎问题的根源在于observeRefreshAction方法。这个方法创建了一个PublishSubject，当设置了refreshActionPublisher之后，立即调用了updateRefreshButtonState方法。这个方法通过调用hasObservers来检查PublishSubject是否有任何订阅者，而结果几乎总是false。这是因为PublishSubject尚未返回到Presenter，在那里我可以订阅它。

有没有办法解决这个问题？我已经尝试将updateRefreshButtonState移到doOnSubscribe中，但没有帮助。

class PageInteractor {
    private var isRefreshActionEnabled = false
    private val refreshStatePublisher by lazy {
        BehaviorSubject.create<Boolean>().apply {
            onNext(false)
        }
    }
    private var refreshActionPublisher: PublishSubject<Unit>? = null

    fun observeRefreshButtonState(): Observable<Boolean> {
        return refreshStatePublisher
    }

    fun observeRefreshAction(): Observable<Unit> {
        if (refreshActionPublisher?.hasComplete() == false && refreshActionPublisher?.hasObservers() == true) {
            refreshActionPublisher?.onComplete()
        }

        return PublishSubject.create<Unit>()
            .also {
                refreshActionPublisher = it
                updateRefreshButtonState()
            }
            .doOnDispose {
                updateRefreshButtonState()
            }
    }

    fun setRefreshActionEnabled(value: Boolean) {
        if (isRefreshActionEnabled != value) {
            isRefreshActionEnabled = value
            updateRefreshButtonState()
        }
    }

    fun onRefreshAction() {
        refreshActionPublisher?.onNext(Unit)
    }

    private fun updateRefreshButtonState() {
        refreshStatePublisher.onNext(refreshActionPublisher?.hasComplete() == false
            && refreshActionPublisher?.hasObservers() == true)
    }
}

class PagePresenter(
        private val pageInteractor: PageInteractor
) : MvpPresenter<PageView> {
    override fun onFirstViewAttach() {
        super.onFirstViewAttach()

        pageInteractor
            .observeRefreshButtonState()
            .subscribe { isEnabled ->
                viewState.setRefreshButtonEnabled(isEnabled)
            }
            .addTo(disposable)
    }

    fun onRefreshButtonClicked() {
        pageInteractor.onRefreshAction()
    }
}

答案1

得分: 1

我试图理解这个问题，然后编写了一些代码并添加了一些注释。
所以你不需要额外的Publish Subject来调用动作，你只需要调用 `onRefreshAction()` 并改变 refreshButtonState 的当前状态。

```kotlin
import io.reactivex.Observable
import io.reactivex.subjects.BehaviorSubject
import kotlin.random.Random

class PageInteractor {

    // 初始值为 false，订阅后，订阅者将收到该值
    private val refreshButtonState = BehaviorSubject.createDefault(false)

    fun observeRefreshButtonState(): Observable<Boolean> = refreshButtonState.distinctUntilChanged()

    // 调用刷新动作
    fun onRefreshAction() {
        // 改变状态或切换状态或执行其他操作
        // 目前生成随机的下一个状态
        val nextAction = Random.nextBoolean()
        refreshButtonState.onNext(nextAction)
    }
}

<details>
<summary>英文:</summary>

I tried to understand the problem and I wrote some piece of code and added some comments.
So you don&#39;t need extra Publish Subject to invoke action, you can just call `onRefreshAction()` and change current state of refreshButtonState.

import io.reactivex.Observable
import io.reactivex.subjects.BehaviorSubject
import kotlin.random.Random

class PageInteractor {

// Initial value is false and after subscription, subscriber will receive that value
private val refreshButtonState = BehaviorSubject.createDefault(false)

fun observeRefreshButtonState(): Observable<Boolean> = refreshButtonState.distinctUntilChanged()

// Invoke refresh action
fun onRefreshAction() {
    // Change state or toggle state or something else
    // Currently generate random next state
    val nextAction = Random.nextBoolean()
    refreshButtonState.onNext(nextAction)
}

}

</details>