......
                cmd_MD_MAIN.CommandText = "SELECT * FROM table AS t";
                da_MD_MAIN.FillSchema(ds_MD_MAIN, SchemaType.Source);
                da_MD_MAIN.Fill(ds_MD_MAIN, "t");
                bs_MD_MAIN = new BindingSource(ds_MD_MAIN, "t");
                .....
                 _txtTAB_TEXT1.DataBindings.CollectionChanged += 
                           new System.ComponentModel.CollectionChangeEventHandler(this._txtTAB_TEXT1_CollectionChange);

                _txtTAB_TEXT1.DataBindings.Add(new Binding("Text", bs_MD_MAIN, "FieldName"));
                .....
                private void _txtTAB_TEXT1_CollectionChange(Object sender, CollectionChangeEventArgs e)
                {
                   Binding bindingObj = (e.Element as Binding);

                        DataView sourceView = null;
                        BindingMemberInfo bindingMemberInfoObj = bindingObj.BindingMemberInfo;

                           sourceView = ((bindingObj.DataSource as BindingSource).List as DataView);

                           string bindedFieldName = bindingMemberInfoObj.BindingField;

                           if (sourceView.Table.Columns[bindedFieldName].MaxLength < 0)
                              {
                                      MessageBox.Show("-1");
                              }
                 
                ....
                }