A radio group contains a set of cells of radio types. Use the CellHasRadioButton property to set the cell of radio type. To change the state for a cell you can use the CellState property. To add or remove a cell to a given radio group you have to use CellHasRadioButton property. Use the CellRadioGroup property to add cells in the same radio group. The control fires the CellStateChanged event when the check box or radio button state is changed.

The following VB sample groups all cells on the first column into a radio group, and display the cell's checked on the radio group when the state of a radio group is changed:

Private Sub Tree1_AddItem(ByVal Item As EXTREELibCtl.HITEM)
    Tree1.Items.CellHasRadioButton(Item, 0) = True
    Tree1.Items.CellRadioGroup(Item, 0) = 1234 ' The 1234 is arbirary and it represents the identifier for the radio group
End Sub

Private Sub Tree1_CellStateChanged(ByVal Item As EXTREELibCtl.HITEM, ByVal ColIndex As Long)
    Debug.Print "In the 1234 radio group the """ & Tree1.Items.CellCaption(, Tree1.Items.CellChecked(1234)) & """ is checked."
End Sub

The following C++ sample groups the radio cells on the first column, and displays the caption of the checked radio cell:

#include "Items.h"
COleVariant vtColumn( long(0) );
CItems items = m_tree.GetItems();
m_tree.BeginUpdate();
for ( long i = 0; i < items.GetItemCount(); i++ )
{
	COleVariant vtItem( items.GetItemByIndex( i ) );
	items.SetCellHasRadioButton( vtItem, vtColumn, TRUE );
	items.SetCellRadioGroup( vtItem, vtColumn, 1234 );
}
m_tree.EndUpdate();

where V2S helper function converts a VARIANT to a string:

static CString V2S( VARIANT* pv, LPCTSTR szDefault = _T("") )
{
	if ( pv )
	{
		if ( pv->vt == VT_ERROR )
			return szDefault;

		COleVariant vt;
		vt.ChangeType( VT_BSTR, pv );
		return V_BSTR( &vt );
	}
	return szDefault;
}

void OnCellStateChangedTree1(long Item, long ColIndex) 
{
	CItems items = m_tree.GetItems();
	long hCell = items.GetCellChecked( 1234 );
	COleVariant vtMissing; V_VT( &vtMissing ) = VT_ERROR;
	OutputDebugString( V2S( &items.GetCellCaption( vtMissing, COleVariant( hCell ) ) ) );
}

The following VB.NET sample groups the radio cells on the first column, and displays the caption of the checked radio cell:

With AxTree1
    .BeginUpdate()
    With .Items
        Dim k As Integer
        For k = 0 To .ItemCount - 1
            .CellHasRadioButton(.ItemByIndex(k), 0) = True
            .CellRadioGroup(.ItemByIndex(k), 0) = 1234
        Next
    End With
    .EndUpdate()
End With

Private Sub AxTree1_CellStateChanged(ByVal sender As Object, ByVal e As AxEXTREELib._ITreeEvents_CellStateChangedEvent) Handles AxTree1.CellStateChanged
    With AxTree1.Items
        Debug.WriteLine(.CellCaption(, .CellChecked(1234)))
    End With
End Sub

The following C# sample groups the radio cells on the first column, and displays the caption of the checked radio cell:

axTree1.BeginUpdate();
EXTREELib.Items items = axTree1.Items;
for (int i = 0; i < items.ItemCount; i++)
{
	items.set_CellHasRadioButton(items[i], 0, true);
	items.set_CellRadioGroup(items[i], 0, 1234);
}
axTree1.EndUpdate();

private void axTree1_CellStateChanged(object sender, AxEXTREELib._ITreeEvents_CellStateChangedEvent e)
{
	string strOutput = axTree1.Items.get_CellCaption( 0, axTree1.Items.get_CellChecked(1234) ).ToString();
	strOutput += " state = " + axTree1.Items.get_CellState(e.item, e.colIndex).ToString() ;
	System.Diagnostics.Debug.WriteLine( strOutput );
}

The following VFP sample groups the radio cells on the first column, and displays the caption of the checked radio cell:

thisform.Tree1.BeginUpdate()
with thisform.Tree1.Items
	local i
	for i = 0 to .ItemCount - 1
		.DefaultItem = .ItemByIndex(i)
		.CellHasRadioButton( 0,0 ) = .t.
		.CellRadioGroup(0,0) = 1234
	next
endwith
thisform.Tree1.EndUpdate()

Note: A cell is identified by the intersection of an item and a column. Properties that have Item and ColIndex parameters let you specify a cell in different ways. The Item parameter identifies the item, while the ColIndex parameter identifies the column.

The Item parameter can be the handle of an item. The ColIndex parameter can specify the column by its index (a numerical value, see the Column.Index property), by its caption (a string value, see the Column.Caption property), or by a cell handle returned by the ItemCell property.

For example, the following statement sets the Bold property of the cell at the intersection of the first item and the first column. The Item parameter is omitted because the ColIndex parameter receives the cell handle returned by ItemCell.

Tree1.Items.CellBold(, Tree1.Items.ItemCell(Tree1.Items(0), 0)) = True

The same cell can be specified by passing the item handle and the column index separately:

Tree1.Items.CellBold(Tree1.Items(0), 0) = True

You can also specify the column by its caption instead of its numerical index:

Tree1.Items.CellBold(Tree1.Items(0), "ColumnName") = True