Adding Hyperlink support to the MFC Grid Control

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Introduction

This article introduces a new cell class for the MFC Grid Control that provides hyperlinks in cells.

The class

To create the class we simply derive a cell from CGridCell. Deriving a cell CGridCell allows us to maintain the functionality of the normal cell, add add our own url support. For our new url cell, we will need to handle the draw, click, cursor, URL color, and URL parsing. We add a COLORREF variable to store the URL color. m_clrUrl will store our URL set by SetUrlColor(COLORREF clr) or the defualt color of GetSysColor(COLOR_HIGHLIGHT). To handle the draw function, we declare:

#include "GridCtrl_Src\GridCell.h"
//.... 
virtual BOOL Draw(CDC* pDC, int nRow, int nCol, CRect rect, BOOL bEraseBkgnd = TRUE); 

We then we parse the cell text for a URL, and if it has a URL we draw the cell with our highlight color, otherwise we draw the cell as normal. We store the cell rect before drawing so that we know our bounds when trying to figure out if a URL was clicked.

BOOL CGridURLCell::Draw(CDC* pDC, int nRow, int nCol, CRect rect, BOOL bEraseBkgnd)
{
	// If URL is present then change text color
	if (HasUrl(GetText()))
		SetTextClr(m_clrUrl);

	// Good a place as any to store the bounds of the rect
	m_Rect = rect;

	return CGridCell::Draw(pDC, nRow, nCol, rect, bEraseBkgnd);
} 

HasUrl(CString str) searches the cell text for one of the known URL prefixes. We store the known prefixes in a URLStruct with the prefixes and string length. The URLStruct contains the prefixes in order from most to least commonly used. HasUrl() retreives one prefix at a time, then searches the cell text before retreiving the next prefix. If a URL prefix is found, then TRUE is returned, else we keep searching and otherwise return FALSE.

// Possible prefixes that indicate a hyperlink
URLStruct CGridURLCell::g_szURIprefixes[] = { 
	{ _T("www."), _tcslen(_T("www.")) },
	{ _T("http:"), _tcslen(_T("http:")) },
	{ _T("mailto:"), _tcslen(_T("mailto:")) },
	{ _T("ftp:"), _tcslen(_T("ftp:")) },
	{ _T("ftp."), _tcslen(_T("ftp.")) },
	{ _T("https:"), _tcslen(_T("https:")) },
	{ _T("news:"), _tcslen(_T("news:")) },
	{ _T("gopher:"), _tcslen(_T("gopher:")) },
	{ _T("telnet:"), _tcslen(_T("telnet:")) },
	{ _T("url:"), _tcslen(_T("url:")) },
	{ _T("file:"), _tcslen(_T("file:")) }
};

BOOL CGridURLCell::HasUrl(CString str)
{
	int nNumPrefixes = sizeof(g_szURIprefixes) / sizeof(g_szURIprefixes[0]);
	for (int i = 0; i < nNumPrefixes; i++)
		if (str.Find(g_szURIprefixes[i].szURLPrefix) >= 0)
			return TRUE;

	return FALSE;
}

To handle the cursor we call GetHandCursor() in our initialization and store the result in HCURSOR g_hLinkCursor. We override OnSetCursor() so that if we are over a URL then we show the hand cursor, otherwise the normal cursor if shown. This allows us to show the normal cursor over our URL cell, if a URL is not present. This is done by first getting the cursor point, then calling OverURL(CPoint& pt, CString& strURL). OverUrl() translates the point into cell text, then searches to cell if we clicked a URL or normal text, and returns TRUE with the URL in strUrl or else FALSE with the cell text in strUrl.

// Return TRUE if you set the cursor
BOOL CGridURLCell::OnSetCursor()
{
#ifndef _WIN32_WCE
	CString strURL;
	CPoint pt(GetMessagePos());
	GetGrid()->ScreenToClient(&pt);
	pt = pt - m_Rect.TopLeft();

	if (OverURL(pt, strURL))
	{
		SetCursor(g_hLinkCursor);
		return TRUE;
	}
	else
#endif
		return CGridCell::OnSetCursor();
}

#ifndef _WIN32_WCE
// "Default hand cursor" from Paul DiLascia's Jan 1998 MSJ article.
HCURSOR CGridURLCell::GetHandCursor()
{
	if (g_hLinkCursor == NULL) // No cursor handle - load our own
	{
		// Get the windows directory
		CString strWndDir;
		GetWindowsDirectory(strWndDir.GetBuffer(MAX_PATH), MAX_PATH);
		strWndDir.ReleaseBuffer();

		strWndDir += _T("\\winhlp32.exe");
		// This retrieves cursor #106 from winhlp32.exe, which is a hand pointer
		HMODULE hModule = LoadLibrary(strWndDir);
		if( hModule )
		{
			HCURSOR hHandCursor = ::LoadCursor(hModule, MAKEINTRESOURCE(106));
			if( hHandCursor )
			{
				g_hLinkCursor = CopyCursor(hHandCursor);
			}
		}
		FreeLibrary(hModule);
	}

	return g_hLinkCursor;
}
#endif

// here we figure out if we are over a URL or not
BOOL CGridURLCell::OverURL(CPoint& pt, CString& strURL)
{
	BOOL bOverURL = FALSE;
	CSize size = GetTextExtent(GetText());

	// Add left of cell so we know if we clicked on text or not
	pt.x += m_Rect.left;
	CPoint center = m_Rect.CenterPoint();

	if ((m_nFormat & DT_RIGHT) && pt.x >= (m_Rect.right - size.cx))
	{
		bOverURL = TRUE;
	} 
	else if ((m_nFormat & DT_CENTER) && 
		((center.x - (size.cx/2)) <= pt.x) && (pt.x <= (center.x + (size.cx/2))) )
	{
		bOverURL = TRUE;
	}
	else if (pt.x <= (size.cx + m_Rect.left))
	{
		bOverURL = TRUE;
	}

	if (!bOverURL)
		return FALSE;

	// We are over text - but are we over a URL?
	bOverURL = FALSE;
	strURL = GetText();

	// Use float, otherwise we get an incorrect letter from the point
	float width = (float)size.cx/(float)strURL.GetLength();

	// remove left of cell so we have original point again 
	pt.x -= m_Rect.left;
	if (m_nFormat & DT_RIGHT)
	{
		int wide = m_Rect.Width() - size.cx;
		pt.x -= wide;
		if (pt.x <= 0)
			return FALSE;
	}

	if (m_nFormat & DT_CENTER)
	{
		int wide = m_Rect.Width() - size.cx;
		pt.x -= (wide/2);
		if (pt.x <= 0 || pt.x > (size.cx + (wide/2)))
			return FALSE;
	}

	// Turn point into a letter
	int ltrs = (int)((float)pt.x/width);

	// Find spaces before and after letter, process text between
	int endSpace = strURL.Find(_T(' '), ltrs);
	if (endSpace != -1)
		strURL.Delete(endSpace, strURL.GetLength()-endSpace);

	int beginSpace = strURL.ReverseFind(_T(' '));
	if (beginSpace != -1)
		strURL.Delete(0, ++beginSpace);

	// Does text have URL
	return HasUrl(strURL);
}

In OnClick(CPoint PointCellRelative) we check to see if we are supposed to launch a URL automatically, if so we call OverUrl() to retreive the URL to launch, then pass the URL for ShellExecute to launch the defualt browser.

void CGridURLCell::OnClick(CPoint PointCellRelative)
{
#ifndef _WIN32_WCE
	CString strURL;
	if (GetAutoLaunchUrl() && OverURL(PointCellRelative, strURL))
		ShellExecute(NULL, _T("open"), strURL, NULL,NULL, SW_SHOW);
#endif
} 

GetAutoLaunchUrl() and SetAutoLaunchUrl(BOOL bLaunch = TRUE) have been included to allow us to toggle the luanching of URLs. By defualt, URLs are automatically launched when clicked.

To use the cell

To use the new cell class either set a particular cell's cell-type using CGridCtrl::SetCellType, or you can set the entire grid to use the URL cell by calling CGridCtrl::SetDefCellType

For instance, to set cell (1,1) as a URL cell, you would ensure the CGridURLCell class header file was included, and then:

// Set the cell type
m_Grid.SetCellType(1,1, RUNTIME_CLASS(CGridURLCell));

// Set the cell properties
CGridURLCell* cell = (CGridURLCell *)m_Grid.GetCell(1, 1);
cell->...