                 _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

        heightc.isActive = true
        _heightConstraint = heightc
    }
    
    private func _setupContainerViews() {
        _navigationBackItem._view.isHidden = true
        // Add the container view.
        addSubview(_containerView)
        let heightConstraint = _containerView.heightAnchor.constraint(equalToConstant: height)

        guard _earlyCheckingBounds(index, in: _navigationTitleItems) else { return (false, nil) }
        
        let item = _navigationTitleItems[index]
        item.underlyingButton.removeFromSuperview()
        item.underlyingButton.removeTarget(self, action: #selector(_handleDidSelectTitleItem(_:)), for: .touchUpInside)
        
        let _formerTrailingAnchor = index == _navigationTitleItems.startIndex ? _navigationTitleItemView.leadingAnchor : _navigationTitleItems[_navigationTitleItems.index(before: index)].underlyingButton.trailingAnchor
        
        if index == _navigationTitleItems.index(before: _navigationTitleItems.endIndex) {
            if let _firstTitleActionItem = _navigationTitleActionItems.first {
                let _latterLeadingAnchor = _firstTitleActionItem.underlyingButton.leadingAnchor
                _formerTrailingAnchor.constraint(equalTo: _latterLeadingAnchor, constant: -DefaultTabNavigationTitleItemPadding).isActive = true
            } else {
                let _latterLeadingAnchor = _titleItemContentAlignmentView.leadingAnchor
