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？！
[解决办法]
String DWfilter
DWfilter = "(xf_id = ~"" + sle_1.text + "~")"
dw_1.SetFilter(DWfilter)
dw_1.Filter()


[解决办法]
dw_1.setfilter("xf_id='"+sle_1.text+"'")
dw_1.filter()