看看这个方法行不行，附文库链接http://wenku.baidu.com/link?url=UiwbkLc_CJ21ePawTei3v1lEeVA9f0TL8dsrrwuaFpJ0of0OWWg1AtEjr21nn-TE00-C4xxc894ZTI_gVuI3_JLxCZ1vAYz_1bHV8V5NrEC
