CToolTipListCtrl - A CListCtrl derived class providing per SubItem tooltips

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Introduction

Once upon a time, I felt the need to use CListCtrls to display (obviously multi-column-line) mathematical matrices, most of which turned out to have explicitly as individual cell elements entities with physical real-world significance. This either meant that I should scorch for extra-space in my already cluttered form view to accommodate the more explicit, although redundant, data display, or try to find an ingenious alternative.

How about commenting each cell/SubItem with tool/info tips? I immediately remembered Matt Weagle's great article “Using the ListCtrl” that referred to the matter of using info tips through LVS_EX_INFOTIP. Unfortunately, as stated by the MSDN documentation, there is no way of doing this method with more granularity than to comment Items with info tips. I then thought about searching CodeProject for tool tip implementations and prayed to find something done on ListCtrl. Well, although I didn't find exactly what I was looking for, I did discover a great article by Nate Maynard (thanks! I owe you one! :) ) about a CTreeCtrl derived class providing per item tool tip support and thought “why not make my first humble contribution to CodeProject?”.

Well, here it is. Most of my class uses the ideas from Nate Maynard's article, so as to avoid redundancy (ok: I confess! To avoid losing to much time… :) ) I will only address the CListCtrl specifics in this article. Please refer to Mr Maynard's article for further insights on the general issue.

How it works (specifically for CListCtrls)

The two major problems I had to deal with when planning my CToolTipListCtrl were the CListCtrl specific issues:

1. There are no handles for CListCtrl SubItems, so I couldn't use CMap to map the ToolTip strings.

2. The right CListCtrl member to use for hit-testing the SubItems would be SubItemHitTest, which, due to OnToolHitTest being const, would had to have its use be re-evaluated in that particular override…

As for the first problem, I addressed it using CMapStringToString with its CString keys being formed by a simple algorithm: (Item * 100 + SubItem). Not very elegant, but it does solve the problem for list controls with less than 100 SubItems per Item (I hope that's not your case… :) )

The second was a little trickier (or at least it seemed so at first) but then I stumbled through the ListView_SubItemHitTest macro in MSDN which solved my problem.

The only other thing you must be aware of is that the CListCtrl masks differ from the CTreeCtrl‘s on the prefix, which in the earlier must be LVHT_.

The functions

I didn't have much time to override and overload as many base class members as Nate Maynard, but the one's I did I hope (at least for me they did) will do the job. They were

• virtual BOOL DeleteAllItems( )
• virtual BOOL DeleteItem( int nItem )

All the other added functions do the same things as their CToolTipTreeCtrl counterparts, of course having their own adapted arguments and returns. They were

• WORD SetToolTipHitMask(WORD wHitMask)
• virtual BOOL DeleteItem( int nItem )
• virtual void DeleteAllToolTips()
• virtual BOOL SetItemToolTipText( int nItem, int nSubItem, LPCTSTR lpszToolTipText )
• virtual CString GetItemToolTipText( int nItem, int nSubItem )

One last remark: I have added a DeleteAllToolTips statement in the class' destructor so as to avoid memory leakages by not cleaning up.

Conclusion

There you have it, and it works! But is this the end of it?

I think not. You see, there are some unanswered questions. For example, check the note I left on this code-snippet:

         //Deal with UNICODE
      #ifndef _UNICODE
              if (pNMHDR->code == TTN_NEEDTEXTA)
                    lstrcpyn(pTTTA->szText, strTipText, 80);
              else
                     _mbstowcsz(pTTTW->szText, strTipText, 80);
      #else
              if (pNMHDR->code == TTN_NEEDTEXTA)
                     _wcstombsz(pTTTA->szText, strTipText, 80);
              else
                     lstrcpyn(pTTTW->szText, strTipText, 80);
      #endif
         return FALSE;    //We found a tool tip,
                         //tell the framework this message has been handled
////////////////////////////////////////////////////////////////////////////////
// ****** Special note *****
//
// Still don't understand why the function must return FALSE for CListCtrl
// so as not to cause flickering, as opposed to Nate Maynard's derivation
// from CTreeCtrl.
// I have experimented with disabling Tooltips for the control
// and found out that a "ghost" tooltip appears for a fraction of a second...
//
// I am completely at a loss...
// Seems to work, though...
//
////////////////////////////////////////////////////////////////////////////////
                                                     
      }
   }

   return FALSE; //We didn't handle the message,
                 //let the framework continue propagating the message

Why was I forced to return FALSE on the OnToolTipText override, even when the function did find the string? I would appreciate some enlightening, anyone…

As usual, “if you have any suggestions, find errors, or if you just find it useful, please feel free to drop me a line”.