extjs combo的联动问题

	var comboxStore = Ext.create('Ext.data.Store', {

fields: ['value', 'name'],
	    data : [
	        {"value":1, "name":"1"},
	        {"value":2, "name":"2"}
	    ]
	});
	var kcxzStore = Ext.create('Ext.data.Store', {
	    fields: ['kcdm', 'kcmc'],
	    proxy: {
	        type: 'ajax',
	        url:'LessonAction!getLessonByXnXqLsbh.action',
	        reader: {
	            type: 'json',
	            root: 'items',
	            totalProperty: 'results'
	        }
	        
	    }
	});
	
	var xqComb = new Ext.form.ComboBox({
			fieldLabel:"学期" ,
			id:'xq',
			labelWidth :50,
			xtype: 'combobox',
			editable : false,
			allowBlank : false,
			store: comboxStore,
			queryMode : 'remote',
			displayField: 'name',
		    valueField: 'value',
		    listeners: {
		    	'change':function() {
		    		xq = Ext.getCmp('xq').value;
					xn = Ext.getCmp('xn').value;
		    		Ext.apply(kcxzStore.proxy.extraParams, {
                      year: xn,
                      xueqi:xq,
		    		});
		    		kcxzStore.reload();
		    	}
		    },
			handler: function() {
			
			}
		});
	
	xqComb.on('change', function(xqComb, newValue, oldValue) {
		xq = Ext.getCmp('xq').value;
		xn = Ext.getCmp('xn').value;
		Ext.apply(kcxzStore.proxy.extraParams, {
          year: xn,
          xueqi:xq,
		});
		kcxzStore.load();
	});
	
	var kcxzComb = new Ext.form.ComboBox({
		fieldLabel:"课程选择" ,
		id:'kcxz',
		labelWidth :60,
		xtype: 'combobox',
		editable : false,
		allowBlank : false,
		store: kcxzStore,
		queryMode : 'remote',
		displayField: 'kcmc',
	    valueField: 'kcdm',
	    listeners: {
	    	'expand':function() {
	    		xq = Ext.getCmp('xq').value;
				xn = Ext.getCmp('xn').value;
	    		Ext.apply(kcxzStore.proxy.extraParams, {
                  year: xn,
                  xueqi:xq,
              });
	    	}
	    },
		handler: function() {
			
		}
	});

两个combox 第一个改变，想让第二个可以重新加载：

添加

queryMode : 'remote',