posting on friends facebook wall using Iphone application

I want to make an iPhone application through which users can post on their friends wall, i know how to post on my own wall but can't post on fri开发者_Go百科ends wall.

What do I need to do to get the desired result for Facebook?

first time get friend get friend list

[_facebook requestWithGraphPath:@"me/friends" andDelegate:self];

then select friend and post his/her wall

 [_facebook requestWithGraphPath:@"frined_ID/feed" andParams:params andHttpMethod:@"POST" andDelegate:self];