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: '',
            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();

});

Hope it helps! Enjoy!