internal void addAChildWithSingleContentToTabContainer(TabControl container, DockingContainer child)
        {
            container.TabPages.Add(child.Name, child.Name);
            child.SetBounds(0, 0, container.Width, container.Height - TITLE_BAR_HEIGHT);
            container.TabPages[child.Name].Controls.Add(child.Content);
            container.TabPages[child.Name].Tag    = child._id;
            container.TabPages[child.Name].Width  = container.Width;
            container.TabPages[child.Name].Height = container.Height - 20;

            _childId.Add(child.Name, child._id);
            _root.Disconnect(child.Name);
        }
        void addChildOnCenter(DockingContainer child)
        {
            child.SetBounds(0, 0, this.Width, this.Height);

            if (this.getContainerType() == ContainerType.SingleContent) //(Content is TabControl) == false)
            {
                _tabContainer.TabPages.Add(this.Name, this.Name);       //insert current content to tab
                this.Content.Dock = DockStyle.Fill;
                this.Content.SetBounds(0, 0, this.Width, this.Height);
                _tabContainer.TabPages[this.Name].Controls.Add(this.Content);
                _tabContainer.TabPages[this.Name].Tag = this._id;
                _childId.Add(this.Name, this._id);
                //_childId.Add(child.Name, child._id);
                if (child.getContainerType() == ContainerType.SingleContent)
                {
                    addAChildWithSingleContentToTabContainer(_tabContainer, child);
                }
                else //else TabContents
                {
                    addAChildWithTabContentToTabContainer(_tabContainer, child);
                }

                //this.Controls.Remove(Content);

                _tabContainer.Height = this.Height - TITLE_BAR_HEIGHT;
                _tabContainer.Width  = this.Width;
                _tabContainer.Dock   = DockStyle.Fill;

                Content = _tabContainer;

                this.Controls.Add(_tabContainer);

                showTitleBar(true, _tabContainer.TabPages[0].Name);
            }
            else //else TabContents
            {
                if (child.getContainerType() == ContainerType.SingleContent)
                {
                    addAChildWithSingleContentToTabContainer(_tabContainer, child);
                }
                else //else TabContents
                {
                    addAChildWithTabContentToTabContainer(_tabContainer, child);
                }
            }
            //_root.Disconnect(child.Name);
            this.setContainerType(ContainerType.TabContents);
            //this.Name = child.Name; //가장 최근에 선택된 tab의 이름을 가져온다.
            //this._id = _childId[child.Name];
            showTitleBar(true, child.Name);
            _tabContainer.SelectTab(child.Name);
        }