NestedWebViewScrollingSwipeRefreshLayoutFixer.kt

/**
 * The [swipeRefreshLayout] will "steal" the swipe gesture from the [nestedWebView]
 * when the user tries to scroll up on the web page. This class adds a
 * [ViewTreeObserver.OnScrollChangedListener] to [swipeRefreshLayout] to disable
 * refreshing while [nestedWebView] is not scrolled all the way to the top.
 */
class NestedWebViewScrollingSwipeRefreshLayoutFixer(
        private val swipeRefreshLayout: SwipeRefreshLayout,
        private val nestedWebView: WebView)
    : LifecycleObserver {

    private val scrollChangedListener = ViewTreeObserver.OnScrollChangedListener {
        swipeRefreshLayout.isEnabled = nestedWebView.scrollY == 0
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onStart() {
        swipeRefreshLayout.viewTreeObserver.addOnScrollChangedListener(scrollChangedListener)
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onStop() {
        swipeRefreshLayout.viewTreeObserver.removeOnScrollChangedListener(scrollChangedListener)
    }
}