Of all the instruments available on the iPhone, GPS is easily one of the most utilized. Having access to Location Services can greatly enhance user experience in your app by adapting behavior to what best suites your user based on his or her whereabouts. One critical piece to utilizing location services is making sure your code behaves the way you expect. Fortunately, in recent releases of Xcode, Apple has made this job a little bit easier by allowing us to spoof our location in the Simulator and on devices.
The way you decide to utilize Xcode’s location spoofing will depend on how your app will use it. For example, if you’re making a gorgeous weather app for the iPad, you’ll want to spoof a static location to simulate getting a user’s local weather. On the other hand, if your app does something like map a user’s bike ride, you’ll need to spoof a set of locations that simulate a user’s location changing over time. Xcode has some presets you can use for both scenarios, but more than likely you’ll want to construct your own custom data to feed to Xcode.
First, you will create a GPX file. GPX is a standard file format used for expressing GPS locations. The format for GPX files that Xcode looks for is fairly straightforward:
<gpx>
<wpt lat="38.897678" lon="-77.036517"></wpt>
</gpx>
This GPX file gives the latitude and longitude for The White House. Throw that text into a text editor, and save it as WhiteHouse.gpx. In Xcode, open a project you have for an iPhone or iPad app, and build it to your device. Once the app is running on your device, go to Product > Debug > Simulate Location, and select the last option in the list that says “Add GPX File to Project…“, then select the WhiteHouse.gpx file we just created. Xcode will pop up some options for adding the file; the defaults should be fine, so just click on Finish. Now, if you go back to Product > Debug > Simulate Location, you should see WhiteHouse near the top of the list; click on it (you can also get to this list from the debug bar at the bottom of Xcode, just click on the location services arrow icon). Your device should now think you’re at the White House. To check, press the home button on your device to close your app and go to Maps app. If it didn’t seem to work, check Xcode and make sure the location arrow in the debug bar is blue. If it’s still gray, Xcode doesn’t like something about your GPX file.
One thing you might be wondering now is if Maps uses your simulated location, will other apps use it also? The answer is yes. Think about all the apps you have and what they are using location services for. Twitter clients posting your location with tweets, sports apps using your location to black out games, camera apps that put your location into Exif data, apps like Foursquare that check you into places – they will all look at your simulated location. I won’t go into detail here, but you should play around with this; it can be interesting.
Visiting the White House was fun, but what if you are making an app for people to track their sweet rollerblade workouts? You will need to make a GPX file with multiple location points. The format is the same but with more wpt elements that have additional latitude and longitude coordinates. I found a GPX file for the New York City Marathon here but had to make some modifications for Xcode to like it. Grab the modified file here. Click on the location button in the debug bar of Xcode, and select “Add GPX File to Project…” again. Point it to your New York City Marathon file, and accept the defaults as before. Finally, click the location button again, and select New York City Marathon from the list. Now, if you go back into Maps, you should see your blue dot making its way through the New York City Marathon; every rollerblader’s life ambition.
We’ve had quite a day so far. Any developer or tester would be exhausted after visiting The White House and rollerblading the New York City Marathon, so I won’t keep you much longer; just one more thing to show. With your app still running in Xcode, unplug your device (I will not be held responsible for any bootstrap errors that result). If you go back into Maps, you’ll find your rollerblader is stuck hanging out in New York. If you don’t stop your app in Xcode before unplugging your device, your device will continue to use the simulated location until you restart it, or until you plug it back in and turn off the location simulation. This is extremely handy for testing without being tethered to your computer. However, this can also be confusing for your mom when she sees your Facebook post from Antarctica, so don’t forget to turn it off when you have finished playing.
Hopefully, Apple will eventually give us the ability to control how quickly Xcode advances through the file. Maybe if we’re really lucky, they’ll give us a way to easily generate GPX files, or let us just specify a location without the need to create a GPX file. In the meantime, Location Simulation, while requiring a little bit of hands on work, is an extremely handy tool for testing location services in your app.
Update: For some additional information on this topic check out this article from Brandon Alexander, an iOS developer at Black Pixel. He has links for some handy tools and also covers an alternate way to enable location simulation using schemes.