types of expressions must match异常

types of expressions must match错误

代码：dw_1.setfilter('xf_id='+sle_1.text)
dw_1.filter()

都已经是字符窜类型了，还类型不匹配？！
------解决方案--------------------
String DWfilter 
DWfilter = "(xf_id = ~"" + sle_1.text + "~")"
dw_1.SetFilter(DWfilter)
dw_1.Filter()


------解决方案--------------------
dw_1.setfilter("xf_id='"+sle_1.text+"'")
dw_1.filter()