iOS开发 支付宝 支付成功 返回字符串怎么取值

[workersJiaDa]

{
{"alipay_trade_app_pay_response":{"code":"10000","msg":"Success","app_id":"2017021105623558","auth_app_id":"2017021105623558","charset":"utf-8","timestamp":"2017-03-30 10:11:24","total_amount":"0.01","trade_no":"2017033021001004160270782505","seller_id":"2088521544671809","out_trade_no":"Y8NUYD9YI34FJAC"},"sign":"h3LiW6McRMlztuMT+uIg31Jsd9T7DVTvohwVSVwuMduxKbIBA68XEKcWBZAci/ZLAswB0Rfek0p/VuMPQtITofADZkJcuUcym+nPyXV1D7S1KHvTtV3oJKeBehk9l+9IizYS5vKS7KmQh2VCLChKxJSyy1nxfS6MS3uCsVorvBqz4VI1qf0lfaYE+t0awcjPe1CJAuSeZDYQautk55Ukwhe3emEQ8NYRkf5WiSEQiRZbn7g3/Be348lQ/VEIsb63EwlsF6pH9ZAUALRxSWFSaqQmW1i73QNB++5zZWeonHIJIl+GRSy42jBHUmIRjS5X/qwO/SW+BOzi4ETeqJoHNA= = ,"sign_type":"RSA2"}
}



怎么才能取到这三个参数