Q:

How to find Facebook Friends using the same app

I am creating an app and would like people using the app to find friends using the same app on Facebook. Any help on this would be great.
I know this can be done. I have seen it on Instagram and Tiger Woods 12.

A:

Once you've authorised the user and obtained an access token, you can quickly determine which of their friends have already authorised your app with a call to /me/friends?fields=installed
For the users' friends who have already authorised the app, the result will look like this:
{
   "installed": true, 
   "id": "{USER_ID_GOES_HERE}"
}, 

and for the users who have not already authorised the app, the result will look like this:
{
  "id": "{USER_ID_GOES_HERE}"
}, 

If you're doing this in the iOS SDK you won't see that exact return value, but the SDK should put the results into a data structure you can use, and check for the presence of the 'installed' item
You can also request additional User object fields other than just 'installed', but this is just a quick example to show you how to get the list of friends that use the app

A:

I have solved this problem in very easy way
Step 1= first download FbGraph API
Step 2= use this code for authentication 
NSString *client_id = @"XXXXXXXXXXXXXX";// App id

//alloc and initalize our FbGraph instance
self.fbGraph = [[FbGraph alloc] initWithFbClientID:client_id];

//begin the authentication process.....
[fbGraph authenticateUserWithCallbackObject:self andSelector:@selector(fbGraphCallback:) 
                     andExtendedPermissions:@"user_photos,user_videos,publish_stream,offline_access,user_checkins,friends_checkins"];

Step 3= Copy fbGraphCallback: Method from sample code and put in your controller
Step 4= Use this code to get Friends and it will give u the list of friend and who have same app install They look like
{
   "installed": true, 
   "id": "{USER_ID_GOES_HERE}"
}, 

Code is = 
NSMutableDictionary *variables = [NSMutableDictionary dictionaryWithCapacity:4];

[variables setObject:@"installed" forKey:@"fields"];

FbGraphResponse *fb_graph_response = [fbGraph doGraphGet:@"me/friends" withGetVars:variables];

NSLog(@"getMeinstalled Friends:  %@", fb_graph_response.htmlResponse);

Thats it!!!!!!!!

A:

I know 'iphone' is tagged in the question, but still this answer might help others who will reach here: 
The FQL query to get (just) the ids of all user's friends who are also users of the app is:
SELECT uid FROM user WHERE is_app_user=true AND uid IN (SELECT uid2 FROM friend WHERE uid1 = me())

