If the watch screen is off, the calling sendMessage on the iPhone won't work. You can only send data in real time when the watch screen is on. This is different than when you are using sendMessage from the watch to the iPhone (iPhone screen can be off). This is the block of code I use anytime I call sendMessage from my iPhone code:
// Send messages to any paired apple watch.
func tryWatchSendMessage(message: [String : AnyObject]) {
if self.session != nil && self.session.paired && self.session.watchAppInstalled {
self.session.sendMessage(message, replyHandler: nil) { (error) -> Void in
// If the message failed to send, queue it up for future transfer
self.session.transferUserInfo(message)
}
}
}
Then I setup the apple watch app to have the same handler if it gets the data via sendMessage or transferUserInfo.