Sharing data between an iOS 8 share extension and main app

You should use NSUserDefaults like this:

Save data:

objc

NSUserDefaults *shared = [[NSUserDefaults alloc] initWithSuiteName:@"group.yougroup"];
[shared setObject:object forKey:@"yourkey"];
[shared synchronize];

swift

let defaults = UserDefaults(suiteName: "group.yourgroup")
defaults?.set(5.9, forKey: "yourKey")

Read data:

objc

NSUserDefaults *shared = [[NSUserDefaults alloc] initWithSuiteName:@"group.yougroup"];
id value = [shared valueForKey:@"yourkey"];
NSLog(@"%@",value);

swift

let defaults = UserDefaults(suiteName: "group.yourgroup")
let x = defaults?.double(forKey: "yourKey")
print(x)

This will work fine!