Keeping the indentation level with Drag '& Drop

I can suggest an extension to the Drag and Drop of your TreeView control. The standard drag and drop as in your control will add the drag branch as a child of the drop item. Quite often during drag and drop operations parent items should stay parent items, child items should stay child items, grandchildren should stay grandchildren, etc, etc.

The following allows just that - with a few logical rules of course:

  1. Dragging an item onto another item on the same indentation level (no matter in which branch), will add the dragitem as a sibling of the dropitem, directly following the dropitem.
  2. Dragging an item onto an item of the next higher (parent-level) indentation, will add the dragitem as the last child of the dropitem.

Therefore the indentation level of the dragitem will stay the same after dropping it. Dragging onto lower (child-level) indentation level, and dragging onto more than 1 higher (parent) indentations are not allowed.

Add a member variable:
   BOOL m_bKeepIndentLevel;

In the constructor, initialize this variable:

m_bKeepIndentLevel = FALSE;

When this member is FALSE, the drag and drop operation will work as it currently is. To keep the indentation level, you can change this value to TRUE inside your program, either by directly accessing the variable, or by Get/Set functions.

In the OnLButtonUp() function, add/modify the lines indicated by '->' :


void CTreeCtrlX::OnLButtonUp(UINT nFlags, CPoint point) 
{
      .
      .
      .

      while ((htiParent = GetParentItem(htiParent)) != NULL)
      {
         if (htiParent == m_hDragItem) return;
      }

->    // check for same indentation level

->    HTREEITEM htiPosition = TVI_LAST;

->    if (m_bKeepIndentLevel)
->    {
->       int nDragIndent = GetIndentLevel(m_hDragItem);
->       int nDropIndent = GetIndentLevel(m_hDropItem);
->
->       if (nDragIndent == nDropIndent)
->       {
->          // add after the drop item, as child of drop item's parent
->          htiPosition = m_hDropItem;
->          m_hDropItem = GetParentItem(m_hDropItem);
->       }
->       else if (nDragIndent == (nDropIndent + 1))
->       {
->          // if dropped on 'upper' indentation, add as last child of drop item
->          htiPosition = TVI_LAST;
->       }
->       else
->       {
->          // invalid drop target
->          return;
->       }
->    }

      Expand (m_hDropItem,TVE_EXPAND);

->    HTREEITEM htiNew = CopyBranch(m_hDragItem,m_hDropItem,htiPosition);
      DeleteItem(m_hDragItem);
      .
      .
      .
}

The implementation of GetIndentLevel() is as follows:


int CRTreeCtrl::GetIndentLevel(HTREEITEM hItem)
{
   int iIndent = 0;
   while ((hItem = GetParentItem(hItem)) != NULL)
   {
      iIndent++;
   }
   return iIndent;
}



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Entire organizations suffer when their networks can't keep up and new opportunities are put on hold. Waiting on service providers isn't good business. In these examples, learn how to simplify network management so that your organization can better manage costs, adapt quickly to business demands, and seize market opportunities when they arise.

  • The world of data storage is changing around us as organizations continue to seek ways by which they can leverage cloud-based services. However, simply shifting everything to the public cloud is generally neither desirable nor feasible, so organizations are struggling with finding ways that they can leverage the public cloud and its outcomes where it makes sense and leave everything else on-premises. The Gorilla Guide lays out the key questions and considerations you need to think through in building your …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date