Adding tooltips for item images

One thing Ive never seen ( other than in my applications ) is tooltips
for the item images. I am not saying that none of the commercial application
use tooltips for the item images, but Ive not seen one yet. In fact, in
some of the applications searching through the help file was also fruitless.
I still didnt know what the images meant.

Anyway, heres what needs to be done if you want to implement tooltips
for the item images and I hope you do want to implement them.

Just one more thing before we start implementing the tooltips. Like
the list view control, the new tree view control creates its own tooltip
control but unlike the list view control it does so in both Win95 and WinNT.
Since I couldnt find any documentation for the build in tooltip, I presume
that it is undocumented and susceptible to change. Anyway, in this section,
we use the MFC provided mechanism.

Step 1: Enable tool tips

Enabling tooltip for a window simply requires a call to EnableToolTips(TRUE).
A good place to insert this statement is in the PreSubclassWindow(). No
matter how the control is created, this function is always called by MFC.
The same is not true for the OnCreate() function. OnCreate() is called
only if you create the control by a call to Create() or CreateEx() and
is not called if the control is created from a dialog resource.


void CTreeCtrlX::PreSubclassWindow() 



Step 2: Override the OnToolHitTest() virtual function

The MFC framework calls this function to determine whether or not to display
a tooltip at the given point. The document suggests that a value of 1 be
returned if the point falls over a tool ( over something that we want to
display a tooltip for ). This is not true however. This function should
return different non zero numbers for different tools in the window.

In this funciton we are only handling the case when the mouse is over
item icon or the state icon. You may wish to add tooltips for other elements
of the tree control. In both the cases we compute the bounding rectangle
for the icon and we set the id equal to the handle of the tree item whose
icons falls under the mouse. Note that though we use the same id for the
item icon and the state icon for the same item, the return values are different.
The different return value forces MFC to update the tooltip.

Although, we can specify the tooltip text in this function itself, it
is best not to add too much computing in this function. This function gets
called each time the mouse moves so it might be a good idea if you can
optimize the function.


int CTreeCtrlX::OnToolHitTest(CPoint point, TOOLINFO * pTI) const
	RECT rect;

	UINT nFlags;
	HTREEITEM hitem = HitTest( point, &nFlags );
	if( nFlags & TVHT_ONITEMICON )
		CImageList *pImg = GetImageList( TVSIL_NORMAL );
		IMAGEINFO imageinfo;
		pImg->GetImageInfo( 0, &imageinfo );

		GetItemRect( hitem, &rect, TRUE );
		rect.right = rect.left - 2;
		rect.left -= (imageinfo.rcImage.right + 2);

		pTI->hwnd = m_hWnd;
		pTI->uId = (UINT)hitem;
		pTI->rect = rect;
		return pTI->uId;
	else if( nFlags & TVHT_ONITEMSTATEICON )
		CImageList *pImg = GetImageList( TVSIL_NORMAL );
		IMAGEINFO imageinfo;
		pImg->GetImageInfo( 0, &imageinfo );

		GetItemRect( hitem, &rect, TRUE );
		rect.right = rect.left - (imageinfo.rcImage.right + 2);

		pImg = GetImageList( TVSIL_STATE );
		rect.left = rect.right - imageinfo.rcImage.right ;

		pTI->hwnd = m_hWnd;
		pTI->uId = (UINT)hitem;
		pTI->rect = rect;

		// return value should be different from that used for item icon
		return pTI->uId*2;	      
	return -1;

Step 3: Add handler for TTN_NEEDTEXT

Add a handler for the TTN_NEEDTEXT notification message. This message is
sent by the tooltip control when it needs the text to display in the tooltip.
Since in the previous step, we specified LPSTR_TEXTCALLBACK for the text
we need to handle this notification. The class wizard does not support
this notification and the entry in the message map will have to be done
manually. Good thing too, since we actually have to handle both versions,
e.i. TTN_NEEDTEXTA and TTN_NEEDTEXTW. Here is what the message map looks



And here is what the declaration looks like in the class.

	afx_msg BOOL OnToolTipText( UINT id, NMHDR * pNMHDR, LRESULT * pResult );

And now the function itself. We have to handle the ANSI version and the
UNICODE version of the message somewhat differently. We also ignore the
message from the built in tooltip control. We recognize the message from
the built in tooltip control by the fact that the id is equal to the window
handle of the tree view control and the flags has the TTF_IDISHWND flag
set. Based on the mouse cursor position we determine whether we need to
supply the tooltip text for the item icon or the state icon. The code below
simply supplies the icon index as the tooltip text, but of course, you
would supply something meaningful.

BOOL CTreeCtrlX::OnToolTipText( UINT id, NMHDR * pNMHDR, LRESULT * pResult )
// need to handle both ANSI and UNICODE versions of the message
CString strTipText;
UINT nID = pNMHDR->idFrom;

// Do not process the message from built in tooltip 
if( nID == (UINT)m_hWnd &&
(( pNMHDR->code == TTN_NEEDTEXTA && pTTTA->uFlags & TTF_IDISHWND ) ||
( pNMHDR->code == TTN_NEEDTEXTW && pTTTW->uFlags & TTF_IDISHWND ) ) )
return FALSE;

// Get the mouse position
const MSG* pMessage;
CPoint pt;
pMessage = GetCurrentMessage();
ASSERT ( pMessage );
pt = pMessage->pt;
ScreenToClient( &pt );

UINT nFlags;
HTREEITEM hitem = HitTest( pt, &nFlags );
if( nFlags & TVHT_ONITEMICON )
int nImage, nSelImage;
GetItemImage( (HTREEITEM ) nID, nImage, nSelImage );
strTipText.Format( "Image : %d", nImage );
strTipText.Format( "State : %d", GetItemState( (HTREEITEM ) nID, 

#ifndef _UNICODE
if (pNMHDR->code == TTN_NEEDTEXTA)
lstrcpyn(pTTTA->szText, strTipText, 80);
_mbstowcsz(pTTTW->szText, strTipText, 80);
if (pNMHDR->code == TTN_NEEDTEXTA)
_wcstombsz(pTTTA->szText, strTipText, 80);
lstrcpyn(pTTTW->szText, strTipText, 80);
*pResult = 0;

return TRUE;    // message was handled


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