关于ios--URL解码成JSON 的问题

得到响应如下：

param=%7B%22paymentMode%22:%22%22,%22transactionId%22:%2231674%22,%22pgRespCode%22:%223%22,%22TxMsg%22:%22Canceled%20by%20user%22,%22authIdCode%22:%22%22,%22currency%22:%22INR%22,%22amount%22:%221.00%22,%22addressStreet1%22:%22Sesame%20street%22,%22addressStreet2%22:%22%22,%22isCOD%22:%22%22,%22loadStatus%22:%22fail%22,%22TxId%22:%22123456%22,%22addressCountry%22:%22India%22,%22firstName%22:%22Ankur%22,%22TxGateway%22:%22%22,%22signature%22:%2245558eb93513aa7a4f2fba24e0ba577b26eb5f40%22,%22addressState%22:%22Pune%22,%22lastName%22:%22Arya%22,%22addressCity%22:%22%22,%22TxRefNo%22:%22CTX1307151506338704178%22,%22loadAmount%22:%221.00%20INR%22,%22pgTxnNo%22:%22CTX1307151506338704178%22,%22TxStatus%22:%22CANCELED%22,%22email%22:%22daredevil.suyash@gmail.com%22,%22issuerRefNo%22:%22%22,%22mobileNo%22:%229900414420%22,%22addressZip%22:%22411045%22%7D

怎么能解码成下面的呢：

param={"paymentMode":"","transactionId":"31674","pgRespCode":"3","TxMsg":"Canceled by user","authIdCode":"","currency":"INR","amount":"1.00","addressStreet1":"Sesame street","addressStreet2":"","isCOD":"","loadStatus":"fail","TxId":"123456","addressCountry":"India","firstName":"Ankur","TxGateway":"","signature":"45558eb93513aa7a4f2fba24e0ba577b26eb5f40","addressState":"Pune","lastName":"Arya","addressCity":"","TxRefNo":"CTX1307151506338704178","loadAmount":"1.00 INR","pgTxnNo":"CTX1307151506338704178","TxStatus":"CANCELED","email":"daredevil.suyash@gmail.com","issuerRefNo":"","mobileNo":"9900414420","addressZip":"411045"}