                 _trailingConstraintOfLastTitleActionItemLabel = _trailingOfTitleActionItems
             }
         } else {
-            let _trailingAnchor = navigationTitleItems.last?._button.trailingAnchor ?? navigationTitleItemView.leadingAnchor
+            let _trailingAnchor = navigationTitleItems.last?.underlyingButton.trailingAnchor ?? navigationTitleItemView.leadingAnchor
             _itemButton.leadingAnchor.constraint(equalTo: _trailingAnchor, constant: DefaultTabNavigationTitleItemPadding).isActive = true
             
             if let _trailing = transition ? _trailingConstraintOfLastTransitionTitleItemLabel : _trailingConstraintOfLastTitleItemLabel {
                 navigationTitleItemView.removeConstraint(_trailing)
             }
             
-            let _trailing = NSLayoutConstraint(item: navigationTitleActionItems.first?._button ?? titleItemContentAlignmentView, attribute: .leading, relatedBy: .equal, toItem: _itemButton, attribute: .trailing, multiplier: 1.0, constant: DefaultTabNavigationTitleItemPadding)
+            let _trailing = NSLayoutConstraint(item: navigationTitleActionItems.first?.underlyingButton ?? titleItemContentAlignmentView, attribute: .leading, relatedBy: .equal, toItem: _itemButton, attribute: .trailing, multiplier: 1.0, constant: DefaultTabNavigationTitleItemPadding)
             navigationTitleItemView.addConstraint(_trailing)
             if transition {
                 _trailingConstraintOfLastTransitionTitleItemLabel = _trailing

        
        _leadingConstraintOfLastItemView = _leadingConstraintOfLastTransitionItemView
        _widthOfNavigationItemViewForZeroContent = _widthOfTransitionNavigationItemViewForZeroContent
        _constraintBetweenTitleContainerAndItemsContainer = _constraintBetweenTransitionTitleContainerAndItemsContainer
        
        _itemsContainerView = navigationItemViews.itemsContainerView
        _itemsScrollView = navigationItemViews.itemsScrollView

        heightc.isActive = true
        _heightConstraint = heightc
    }
    /// Constraint container views of the title(navigation) items.
    private func _constraintContainerViews() {
        _navigationBackItem.underlyingView.isHidden = true
        // Add the container view.
        addSubview(_containerView)
        let heightConstraint = _containerView.heightAnchor.constraint(equalToConstant: height)
