为什么Extjs继承Ext.data.Store不起作用

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); 
 } 
});