Adding tooltips for item images

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

void CTreeCtrlX::PreSubclassWindow() 
{
	CTreeCtrl::PreSubclassWindow();

	EnableToolTips(TRUE);
}

Step 2: Override the OnToolHitTest() virtual function

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->lpszText = LPSTR_TEXTCALLBACK;
		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->lpszText = LPSTR_TEXTCALLBACK;
		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

BEGIN_MESSAGE_MAP(CTreeCtrlX, CTreeCtrl)
	//{{AFX_MSG_MAP(CTreeCtrlX)
	:
	:
	//}}AFX_MSG_MAP
	ON_NOTIFY_EX_RANGE(TTN_NEEDTEXTW, 0, 0xFFFF, OnToolTipText)
	ON_NOTIFY_EX_RANGE(TTN_NEEDTEXTA, 0, 0xFFFF, OnToolTipText)
END_MESSAGE_MAP()

protected:
	//{{AFX_MSG(CTreeCtrlX)
	:
	:
	//}}AFX_MSG
	afx_msg BOOL OnToolTipText( UINT id, NMHDR * pNMHDR, LRESULT * pResult );
	DECLARE_MESSAGE_MAP()

BOOL CTreeCtrlX::OnToolTipText( UINT id, NMHDR * pNMHDR, LRESULT * pResult )
{
	// need to handle both ANSI and UNICODE versions of the message
	TOOLTIPTEXTA* pTTTA = (TOOLTIPTEXTA*)pNMHDR;
	TOOLTIPTEXTW* pTTTW = (TOOLTIPTEXTW*)pNMHDR;
	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 );
	}
	else
	{
		strTipText.Format( "State : %d", GetItemState( (HTREEITEM ) nID, 
				    	TVIS_STATEIMAGEMASK ) );
	}

#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
	*pResult = 0;

	return TRUE;    // message was handled
}