extjs combobox下拉框 聯動

js檔案(兩個下拉框)：

{
    columnWidth : .5,
    layout : "form",
    items : [{
     xtype : 'combo',
     id : 'bname',
     hiddenName : "tname",
     fieldLabel : '<div style=\"vertical-align:middle;color:red;display:inline\">*</div>表名稱',
     triggerAction : 'all',
     forceSelection : true,
     mode : 'remote',
     emptyText : '請選擇..',
     valueField : 'tname',
     displayField : 'tzname',
     multiSelect : true,
     editable : false,
     queryMode : 'local',
     width : 160,
     store : store,
     listeners : {
      change : function() {
       var com1zhi = Ext.getCmp("bname");
       if (com1zhi == "") {
        return;
       }
       
       //Ext.getStore('myStoreId')=ds
      }
     },
     listeners : { 
                  select : function() { 
                          try { 
                                  var parent = Ext.getCmp('combo2');
                                  // var combo2 = Ext.getCmp("combo2");
                   parent.clearValue();
                                  parent.store.reload({ 
                                              params : { 
                                                      tablename :this.value  //傳到action的參數                                     

                 } 
                                              }); 
                                            
                              }catch (ex)  
                              { 
                                  Ext.MessageBox.alert(ex); 
                              } 
                          } 
                    }, 

     typeAhead : true
    }]

},{

      columnWidth : .5,
      layout : "form",
      items : [{
         fieldLabel : '欄位列表',
         xtype : "lovcombo",
         hiddenName : "column_name",
         name : 'column_name',// 和valuefield
         id : 'combo2',
         displayField : 'comments', // 對應下面的資料項目
         valueField : 'column_name',
         editable : false,
         triggerAction : 'all',
         hideOnSelect : false,
         mode : "local",
         emptyText : "請選擇..",
         width : 160,
         scope : this,
         store : ds,
         readOnly : false
        }]
     

}

action 方法：這個就省了……