问题
This is on watchOS 4.3 beta (15T5165e) and Xcode 9.3 beta (9Q98q), but I don't think it's because of them being in beta because another WatchKit project ran on device just fine. I have tried unpairing/repairing, restarting the iPhone/Watch/macOS/Xcode (while making sure to to tap "trust this computer" on the watch) but Xcode still says "Running" in the WatchKit scheme without actually installing and running the watchOS app, eventually saying "Watch app launch timed out."
来源：https://stackoverflow.com/questions/48479528/xcode-does-not-install-watchos-app-for-debugging-on-device