研究3

繼續觀察- (void)_updateVisibleContentRects的內容：

- (void)_updateVisibleContentRects
{
    BOOL inStableState = _visibleContentRectUpdateScheduledFromScrollViewInStableState;

    if (![self usesStandardContentView]) {
        [_passwordView setFrame:self.bounds];
        [_customContentView web_computedContentInsetDidChange];
        return;
    }

    if (_delayUpdateVisibleContentRects) {
        _hadDelayedUpdateVisibleContentRects = YES;
        return;
    }

    if (_dynamicViewportUpdateMode != DynamicViewportUpdateMode::NotResizing
        || (_needsResetViewStateAfterCommitLoadForMainFrame && ![_contentView sizeChangedSinceLastVisibleContentRectUpdate])
        || [_scrollView isZoomBouncing]
        || _currentlyAdjustingScrollViewInsetsForKeyboard)
        return;

    CGRect fullViewRect = self.bounds;
    CGRect visibleRectInContentCoordinates = [self _visibleContentRect];

    UIEdgeInsets computedContentInsetUnadjustedForKeyboard = [self _computedContentInset];
    if (!_haveSetObscuredInsets)
        computedContentInsetUnadjustedForKeyboard.bottom -= _totalScrollViewBottomInsetAdjustmentForKeyboard;

    CGFloat scaleFactor = contentZoomScale(self);

    CGRect unobscuredRect = UIEdgeInsetsInsetRect(fullViewRect, computedContentInsetUnadjustedForKeyboard);
    CGRect unobscuredRectInContentCoordinates = _frozenUnobscuredContentRect ? _frozenUnobscuredContentRect.value() : [self convertRect:unobscuredRect toView:_contentView.get()];
    unobscuredRectInContentCoordinates = CGRectIntersection(unobscuredRectInContentCoordinates, [self _contentBoundsExtendedForRubberbandingWithScale:scaleFactor]);

#if ENABLE(CSS_SCROLL_SNAP) && ENABLE(ASYNC_SCROLLING)
    if (inStableState) {
        WebKit::RemoteScrollingCoordinatorProxy* coordinator = _page->scrollingCoordinatorProxy();
        if (coordinator && coordinator->hasActiveSnapPoint()) {
            CGRect unobscuredRect = UIEdgeInsetsInsetRect(fullViewRect, computedContentInsetUnadjustedForKeyboard);

            CGPoint currentPoint = [_scrollView contentOffset];
            CGPoint activePoint = coordinator->nearestActiveContentInsetAdjustedSnapPoint(unobscuredRect.origin.y, currentPoint);

            if (!CGPointEqualToPoint(activePoint, currentPoint)) {
                RetainPtr<WKScrollView> strongScrollView = _scrollView;
                dispatch_async(dispatch_get_main_queue(), [strongScrollView, activePoint] {
                    [strongScrollView setContentOffset:activePoint animated:NO];
                });
            }
        }
    }
#endif

    [_contentView didUpdateVisibleRect:visibleRectInContentCoordinates
        unobscuredRect:unobscuredRectInContentCoordinates
        unobscuredRectInScrollViewCoordinates:unobscuredRect
        obscuredInsets:_obscuredInsets
        unobscuredSafeAreaInsets:[self _computedUnobscuredSafeAreaInset]
        inputViewBounds:_inputViewBounds
        scale:scaleFactor minimumScale:[_scrollView minimumZoomScale]
        inStableState:inStableState
        isChangingObscuredInsetsInteractively:_isChangingObscuredInsetsInteractively
        enclosedInScrollableAncestorView:scrollViewCanScroll([self _scroller])];

    while (!_visibleContentRectUpdateCallbacks.isEmpty()) {
        auto callback = _visibleContentRectUpdateCallbacks.takeLast();
        callback();
    }
}

這個function看起來的確就是WKWebView的畫面更新關鍵，WKContentView更新畫面時只會更新視窗可見範圍，實際測試時Ｗeb頁面在UITableView滾動時，畫面也更新的不太即時。找到這個function後，接下來就是找出何時會觸發這個function的時機，推論讓Web頁面完整呈現的解決方案。

未完繼續...