Extjs3.0 C#后台获取ComboBox选中值的有关问题

 new Ext.form.ComboBox({

                               name: 'levelbox',

                               fieldLabel: '商务级别',

                               valueField: 'LevelID',

                               displayField: 'LevelName',

                               hiddenName: 'LevelID',

                               triggerAction: 'all',

                               typeAhead: true,

                               mode: 'local',

                               store: store

                           }),

                          new Ext.form.TextArea({

                              width: '350',

                              grow: true,

                              name: 'textareabox',

                              preventScrollbars: true,

                              fieldLabel: '工作备注',

                              allowBank: false,

                              emptyText: '暂无',

                              maxLength: 50,

                              minLength: 10