Adding Advanced Checkbox

Step 1: Create bitmap with checkbox images

Step 2: Initialize the state image list

	m_tree.m_imageState.Create( IDB_STATE, 13, 1, RGB(255,255,255) );
	m_tree.SetImageList( &(m_tree.m_imageState), TVSIL_STATE );

Step 3: Insert items with the checkbox as a state image

SetItemState( hItem, INDEXTOSTATEIMAGEMASK(1), TVIS_STATEIMAGEMASK );

Step 4: Add enumeration for check operation and state

// Attributes
public:
	enum CheckState{ NOSTATE = 0, UNCHECKED, CHECKED, CHILD_CHECKED, 
		SELF_AND_CHILD_CHECKED };
	enum CheckType{ CHECK, UNCHECK, TOGGLE, REFRESH };

Step 5: Define SetCheck() function

Depending on the value of nCheck, the function determines what the new state of the item should be. If nCheck is REFRESH, only the immediate children items are scanned to determine if the checkbox should be red ( to indicate that a child is checked ). The function then updates the parent items.

// SetCheck	- Check, uncheck, toggle or refresh an item
// hItem	- Item that is to be updated
// nCheck	- CHECK, UNCHECK, TOGGLE OR REFRESH 
BOOL CTreeCtrlX::SetCheck( HTREEITEM hItem, CheckType nCheck )
{
	if( hItem == NULL ) 
		return FALSE;

	UINT nState = GetItemState( hItem, TVIS_STATEIMAGEMASK ) >> 12;

	// Determine the new check state
	if ( nCheck == CHECK )
	{
		if( nState == CHECKED || nState == SELF_AND_CHILD_CHECKED )
			return TRUE;
		switch( nState )
		{
		case UNCHECKED:		nState = CHECKED; break;
		case CHILD_CHECKED:		nState = SELF_AND_CHILD_CHECKED; break;
		}
	}
	else if( nCheck == UNCHECK )
	{
		if( nState == UNCHECKED || nState == CHILD_CHECKED )
			return TRUE;
		switch( nState )
		{
		case CHECKED:			nState = UNCHECKED; break;
		case SELF_AND_CHILD_CHECKED:	nState = CHILD_CHECKED; break;
		}
	}
	else if( nCheck == TOGGLE )
	{
		switch( nState )
		{
		case UNCHECKED:		nState = CHECKED; break;
		case CHECKED:			nState = UNCHECKED; break;
		case CHILD_CHECKED:		nState = SELF_AND_CHILD_CHECKED; break;
		case SELF_AND_CHILD_CHECKED:	nState = CHILD_CHECKED; break;
		}
	}
	else if( nCheck == REFRESH )
	{
		// Scan children to determine new state
		BOOL bChildSelected = FALSE;
		HTREEITEM htiChild = GetChildItem( hItem );

		// Scan children
		while( htiChild )
		{
			UINT nChildState = GetItemState( htiChild, 
						TVIS_STATEIMAGEMASK ) >> 12;
			if( nChildState != UNCHECKED && nChildState != NOSTATE )
			{
				bChildSelected = TRUE;
				break;
			}
			htiChild = GetNextItem( htiChild, TVGN_NEXT );
		}
		if( bChildSelected )
		{
			if( nState == CHECKED ) nState = SELF_AND_CHILD_CHECKED;
			else if( nState == UNCHECKED ) nState = CHILD_CHECKED;
		}
		else
		{
			if( nState == SELF_AND_CHILD_CHECKED ) nState = CHECKED;
			else if( nState == CHILD_CHECKED ) nState = UNCHECKED;
		}
	}

	SetItemState( hItem, INDEXTOSTATEIMAGEMASK(nState), 
					TVIS_STATEIMAGEMASK );

	if( nState == CHECKED 
		|| ( REFRESH 
			&& (nState == SELF_AND_CHILD_CHECKED 
				|| nState == CHILD_CHECKED)
			)
		)
	{
		// Mark the parents to indicate that a child item is selected.
		// Use checkbox with red border.
		while( (hItem = GetParentItem( hItem )) != NULL )
		{
			nState = GetItemState( hItem, TVIS_STATEIMAGEMASK ) >> 12;
			if( nState == UNCHECKED )
				SetItemState( hItem, INDEXTOSTATEIMAGEMASK(CHILD_CHECKED), 
						TVIS_STATEIMAGEMASK );
			else if ( nState == CHECKED )
				SetItemState( hItem,
					INDEXTOSTATEIMAGEMASK(SELF_AND_CHILD_CHECKED), 
					TVIS_STATEIMAGEMASK );
		}
	}
	else if( nState == UNCHECKED )
	{
		// Maybe the parent ( ancestors ) state needs to be adjusted if
		// no more children selected.
		while( (hItem = GetParentItem( hItem )) != NULL )
		{
			BOOL bChildSelected = FALSE;
			HTREEITEM htiChild = GetChildItem( hItem );

			// Scan children
			while( htiChild )
			{
				UINT nChildState = GetItemState( htiChild, 
							TVIS_STATEIMAGEMASK ) >> 12;
				if( nChildState != UNCHECKED && nChildState != NOSTATE )
				{
					bChildSelected = TRUE;
					break;
				}
				htiChild = GetNextItem( htiChild, TVGN_NEXT );
			}
			if( bChildSelected )
			{
				// The parent does not need to be updated
				// since there are other children still selected
				break;
			}
			else
			{
				// The parent item has no more children selected. 
				// Mark accordingly
				UINT nParentState = GetItemState( hItem, 
							TVIS_STATEIMAGEMASK ) >> 12;
				if( nParentState == CHILD_CHECKED )
					SetItemState( hItem, 
							INDEXTOSTATEIMAGEMASK(UNCHECKED), 
							TVIS_STATEIMAGEMASK );
				else if ( nParentState == SELF_AND_CHILD_CHECKED )
					SetItemState( hItem, INDEXTOSTATEIMAGEMASK(CHECKED), 
							TVIS_STATEIMAGEMASK );
			}
		}
 	}                                                                                                              
	return TRUE;
}

Step 6: Add code to OnLButtonDown to toggle checkbox

void CTreeCtrlX::OnLButtonDown(UINT nFlags, CPoint point) 
{
	UINT uFlags=0;
	HTREEITEM hItem = HitTest(point,&uFlags;);

	if( uFlags & TVHT_ONITEMSTATEICON )
	{
		SetCheck( hItem, TOGGLE );
		return;
	}
}

Step 7: Add code to OnKeyDown to toggle checkbox

void CTreeCtrlX::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags) 
{
	if( nChar == VK_SPACE )
	{
		HTREEITEM hItem = GetSelectedItem();
		SetCheck( hItem, TOGGLE );
		return;
	}
}

Step 8: Define helper functions

BOOL CTreeCtrlX::IsItemChecked(HTREEITEM hItem)
{
	int iImage = GetItemState( hItem, TVIS_STATEIMAGEMASK )>>12;
	return iImage == CHECKED || iImage == SELF_AND_CHILD_CHECKED;
}

HTREEITEM CTreeCtrlX::GetFirstCheckedItem()
{
	for ( HTREEITEM hItem = GetRootItem(); hItem!=NULL;  )
	{
		int iImage = GetItemState( hItem, TVIS_STATEIMAGEMASK )>>12;
		if ( iImage == CHECKED || iImage == SELF_AND_CHILD_CHECKED )
			return hItem;
		
		if( iImage != CHILD_CHECKED )
		{
			HTREEITEM hti = GetNextItem( hItem, TVGN_NEXT );
			if( hti == NULL )
				hItem = GetNextItem( hItem );
			else 
				hItem = hti;
		}
		else
			hItem = GetNextItem( hItem );
	}

	return NULL;
}

HTREEITEM CTreeCtrlX::GetNextCheckedItem( HTREEITEM hItem )
{
	hItem = GetNextItem( hItem );
	while( hItem!=NULL )
	{
		int iImage = GetItemState( hItem, TVIS_STATEIMAGEMASK )>>12;
		if ( iImage == CHECKED || iImage == SELF_AND_CHILD_CHECKED )
			return hItem;
		
		if( iImage != CHILD_CHECKED )
		{
			HTREEITEM hti = GetNextItem( hItem, TVGN_NEXT );
			if( hti == NULL )
				hItem = GetNextItem( hItem );
			else 
				hItem = hti;
		}
		else
			hItem = GetNextItem( hItem );
	}

	return NULL;
}

HTREEITEM CTreeCtrlX::GetPrevCheckedItem( HTREEITEM hItem )
{
	for ( hItem = GetPrevItem( hItem ); hItem!=NULL; hItem = GetPrevItem( hItem ) )
		if ( IsItemChecked(hItem) )
			return hItem;

	return NULL;
}

The GetNextItem() function with single argument and the GetPrevItem() function have been defined earlier in the Get next item in outline and the Get previous item in outline topics.