Vertical lines for column borders


The list view control does not provide for any visual delineation between the columns in the report mode. The code below shows how to add vertical lines between columns. To do our own drawing we override the OnPaint() function. Since we dont want to do all the rendering of the control, we let DefWindowProc() take care of it before we start drawing the lines. We also make sure that the list view control is indeed in the report mode.


 
void CMyListCtrl::OnPaint() 
{
	// First let the control do its default drawing.
	const MSG *msg = GetCurrentMessage();
	DefWindowProc( msg->message, msg->wParam, msg->lParam );

	// Draw the lines only for LVS_REPORT mode
	if( (GetStyle() & LVS_TYPEMASK) == LVS_REPORT )
	{
		// Get the number of columns
		CClientDC dc(this );
		CHeaderCtrl* pHeader = (CHeaderCtrl*)GetDlgItem(0);
		int nColumnCount = pHeader->GetItemCount();

		// The bottom of the header corresponds to the top of the line 
		RECT rect;
		pHeader->GetClientRect( &rect );
		int top = rect.bottom;

		// Now get the client rect so we know the line length and
		// when to stop
		GetClientRect( &rect );

		// The border of the column is offset by the horz scroll
		int borderx = 0 - GetScrollPos( SB_HORZ );
		for( int i = 0; i < nColumnCount; i++ )
		{
			// Get the next border
			borderx += GetColumnWidth( i );

			// if next border is outside client area, break out
			if( borderx >= rect.right ) break;

			// Draw the line.
			dc.MoveTo( borderx-1, top);
			dc.LineTo( borderx-1, rect.bottom );
		}
	}
	
	// Do not call CListCtrl::OnPaint() for painting messages
}
To draw the vertical lines, we use the header control to determine the column dimensions and also the effective client area after taking into account the header control itself. Finally, we draw a line to the right of each column.

Note that the horizontal scrollbars position is taken into account when determining the border. If we dont do this, we might end up with a line right in the middle of a column when the list has been horizontally scrolled. The GetScrollPos() function returns 0 if there is no scrollbar so we dont need to make a prior check on whether the list view control does have a horizontal scrollbar. We could also have used GetItemRect() function, but it works only if the list has atleast one item.

The line is actually drawn one pixel left of the column border. This aligns it better with the column header. It also introduces a bug. When you increase a column width, the column area below the last visible item is not updated, thus leaving traces of the previous line. There are two approaches you can take to resolve this. First, draw the line exactly on the column border (e.i. do not subtract 1 from borderx). The second approach is to handle the HDN_TRACK notification from the header control and invalidate the exposed area so that it gets redrawn.