iOS dev - Post parameters to an URL with objective-C

In the last months I started to learn objective-C. I was working mostly modifying an existent project. I needed to open a webview wher the parameters are sent by POST method and they has to be passed with content-type "application/x-www-form-urlencoded". So this is the code I used:
Plese notice that in the line 15 and 16 I replace the characters tu escape url codes... If you have better ideas please comment to this post.. Ciao