UI 元素在观察订阅之前检查其状态

Question

我在 Android 应用程序中更新刷新按钮状态时遇到问题。在我的交互器中，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)
    }
}

我在演示器中使用了这个交互器，它是一个 Moxy 演示器。

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被禁用。我做了一些调试，似乎问题的根源在方法 observeRefreshAction 中。此方法在设置 refreshActionPublisher 时创建 PublishSubject，然后立即调用方法 updateRefreshButtonState。此方法通过调用 hasObservers 检查 PublishSubject 是否有任何订阅者，结果几乎总是错误的。发生这种情况是因为 PublishSubject 尚未返回给演示者，我可以在那里订阅它。

有什么方法可以解决这个问题吗？我曾尝试将 updateRefreshButtonState 移动到 doOnSubscribe，但没有帮助。

Answer 1

我试图理解问题并编写了一些代码并添加了一些注释。因此，您不需要额外的 Publish Subject 来调用操作，您只需调用 onRefreshAction() 并更改 refreshButtonState 的当前状态即可。

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)
    }
}

UI 元素在观察订阅之前检查其状态

UI element checks its state before observes subscribes

java

android

rx-java2