The AddColumn event is fired after a new column has been inserted to Columns collection. Use the AddColumn event to associate extra data to a new column. Use the Add method to add new columns to Columns collection. Use the ColumnAutoSize property to fit all visible columns in the control's client area. 

The following VB sample shows how to set the width for all columns:

Private Sub Tree1_AddColumn(ByVal Column As EXTREELibCtl.IColumn)
    Column.Width = 128
End Sub

The following VB.NET sample  changes the column's width when a new column is added:

Private Sub AxTree1_AddColumn(ByVal sender As Object, ByVal e As AxEXTREELib._ITreeEvents_AddColumnEvent) Handles AxTree1.AddColumn
    e.column.Width = 128
End Sub

The following C# sample changes the column's width when a new column is added:

private void axTree1_AddColumn(object sender, AxEXTREELib._ITreeEvents_AddColumnEvent e)
{
	e.column.Width = 128;
}

The following C++ sample changes the column's width when a new column is added:

#include "Column.h"
#include "Columns.h"
void OnAddColumnTree1(LPDISPATCH Column) 
{
	CColumn column( Column );column.m_bAutoRelease = FALSE;
	column.SetWidth( 128 );
}

The following VFP sample changes the column's width when a new column is added:

*** ActiveX Control Event ***
LPARAMETERS column

with column
	.Width = 128
endwith