How to use compiler directives to detect the iOS Simulator

Swift version: 5.6

Paul Hudson @twostraws May 28th 2019

Swift makes it easy to write special code that should be executed only in the iOS Simulator. This is helpful to test situations where the simulator and devices don't match, for example testing the accelerometer or camera.

If you want certain code to be run only in the iOS simulator, you should use this:

#if targetEnvironment(simulator)
// your code
#endif

Any code between the #if and #endif won't even exist when the app is run on devices, so it has zero performance impact. If you want to specify alternate code that should only be run on devices (and never on the simulator) you should use #else, like this:

func updateMotion() {
#if targetEnvironment(simulator)
    // we're on the simulator - calculate pretend movement
    if let currentTouch = lastTouchPosition {
        let diff = CGPoint(x: currentTouch.x - player.position.x, y: currentTouch.y - player.position.y)
        physicsWorld.gravity = CGVector(dx: diff.x / 100, dy: diff.y / 100)
    }
#else
    // we're on a device – use the accelerometer
    if let accelerometerData = motionManager.accelerometerData {
        physicsWorld.gravity = CGVector(dx: accelerometerData.acceleration.y * -50, dy: accelerometerData.acceleration.x * 50)
    }
#endif
}