Ext.tree.TreeLoader怎么传值啊？

#################### 值###########
var beginDate = Ext.getCmp("beginDate").getValue();
var endDate = Ext.getCmp("endDate").getValue();
var group = Ext.getCmp("group").getValue();

var treeLoader = new Ext.tree.TreeLoader({
id : treeLoader,
preloadChildren:true,
dataUrl : 's873J.do?operate=payList&beginDate=',

uiProviders:{
'col': Ext.tree.TreeCheckNodeUI
}
});

想treeLoader .load()时候吧上面3个值传到后台能行么？

var treeLoader = new Ext.tree.TreeLoader({
id : treeLoader,
preloadChildren:true,
dataUrl : 's873J.do?operate=payList&beginDate=',

uiProviders:{
'col': Ext.tree.TreeCheckNodeUI
}
[color=red]baseParams:{
beginDate: Ext.getCmp("beginDate").getValue(),
endDate: Ext.getCmp("beginDate").getValue(),
group: Ext.getCmp("group").getValue()
} [/color]

});

或者

var treeLoader = new Ext.tree.TreeLoader({
id : treeLoader,
preloadChildren:true,
dataUrl : 's873J.do?operate=payList&beginDate=',

uiProviders:{
'col': Ext.tree.TreeCheckNodeUI
}

});

treeLoader.on("beforeload", function(treeLoader, node) {

[color=red] treeLoader.baseParams.beginDate = Ext.getCmp("beginDate").getValue();

treeLoader.baseParams.endDate = Ext.getCmp("beginDate").getValue();

treeLoader.baseParams.group = Ext.getCmp("group").getValue();[/color]

});