ExtJS Combobox 如何设置默认和取值问题

学习ExtJs，如何给combobox选中某一行， 取值问题。 following is for stores combobox var readerLocation = new Ext.data.WCFJsonReader({     root: 'data', id: 'Store', totalProperty: 'totalCount',     fields: [             { name: 'Store', type: 'int' },

            { name: 'StoreName', type: 'string' }

             /*0:'All', '1':'ShangHai', '2':'BeiJing' */

        ] }); var storeStore = new Ext.data.Store({     proxy: new Ext.data.WCFHttpProxy({         url: '/*.svc/GetStoresList'     }),     reader: readerLocation,     remoteSort: true, listeners: {         load: function() {             comboLocation.setValue(comboLocation.getValue());         }     } }); var comboLocation = new Ext.form.ComboBox({     store: storeStore,     displayField: 'StoreName',     valueField: 'Store',     id: 'comboboxStore',     typeAhead: true,     mode: 'local',     triggerAction: 'all',     selectOnFocus: true,     value: '',     width: 180,     applyTo: 'ddlStore' }); storeStore.load(); storeStore.on("load", onstoreStoreLoad, storeStore, true); function onstoreStoreLoad() {     if (storeStore.getTotalCount() > 0)         comboLocation.setValue(storeStore.getAt(0).data.Store); } /*** above is for location ***/

点击按钮 取值like：

Ext.get("btnFilter").on("click", displayGrid);

function displayGrid() {             var storeFilter = comboLocation.getValue(); });