The way to do this is described in the WWDC session on Watch Connectivity. For this kind of immediate communication, you can use WCSession's sendMessage to send data to the app running on the watch. To get the data upon change to the text field, you'll need to implement the delegate method that responds to changes in the text field, then send that data to the watch, and respond to the appropriate delegate calls on the watch when it receives those messages.
Topic:
App & System Services
SubTopic:
General
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