Extjs 继承Ext.data.Store不起作用原因分析及解决

DocStore = Ext.extend(Ext.data.Store,{
initComponent:function(){
this.proxy = new Ext.data.HttpProxy({url:this.url});
this.reader = new Ext.data.JsonReader(
{
totalProperty: 'results',
root: 'rows',
id:'docid',
fields: ['docid', 'extention','docname', 'author', 'sizes', 'datecreated']
}

);
this.sortInfo = { field: 'datecreated', direction: 'DESC' };
this.remoteSort = false;
DocStore.superclass.initComponent.call(this);
}
});