NSUserDefault change notification handling in watchAppExtension

You can try MMWormHole which provides :

• a channel between the iOS device and the watch which enables you to send data back and forth between them.
• Also provides a way to do Notifications without having to handle the file monitoring by urself.

Using it ,That will be all the code needed to do notifications in ur app

[self.wormhole passMessageObject:@{@"buttonNumber" : @(1)} identifier:@"button"];

[self.wormhole listenForMessageWithIdentifier:@"button" 
  listener:^(id messageObject) {
    self.numberLabel.text = [messageObject[@"buttonNumber"] stringValue];
}];

I don't think iOS has capability of distributed notifications between app and extension, notifications will not work between both, instead you need to find a way in which both can monitor changes. For example files.

As you already have created group, you can keep a file in the group folder and add a filewatcher in extension, update the file from app, and filewatcher will catch the change, and your work is done.

For filewatcher see code here.

Hope it helps.

Cheers.

Update

Find File watcher Swift version here. Thanks @rivera for adding.