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All right my friends in this video we're going to write out some code to trick all of our different

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test devices be it a simulated device or a physical into thinking that the user's location is changing

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over time.

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So to get started I'm gonna go back over my code editor and inside of my S R C directory I'm going to

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make a new file called underscore mock location dot J.S. so the idea is that this is kind of like a

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test only file that's going to mark out our users location.

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We would definitely not want to include this file inside of any kind of production build.

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So over time are going to be kind of toggling an import statement to either include this file or not

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use it at all.

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All right.

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So inside of here we're going to first add in a little import statement we're going to say import star

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as location from Expo location.

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So internally at the location library exports a ton of different named functions.

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By using star as location we're essentially getting a single variable that references all those different

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functions then right after that we're gonna write out a little constant variable right here you're going

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to see why we are defining this in just a moment.

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I'm going to say 10 meters with degrees and I'm going to define this as zero point zero zero zero one.

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Like so so this represents 10 meters in longitude or latitude.

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Now technically it's not exactly 10 meters in both longitude and latitude just because the actual physical

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shape of the world.

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But it's essentially close enough after that we're going to define a function called get location.

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This is going to take a variable called increment that's essentially a counter variable so from this

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function right here we are going to return an object that essentially is a fake location reading it's

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going to fake out some fake longitude and latitude and timestamp.

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This is going to be what actually kind of tricks the expo location into thinking that our physical or

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our emulate device is moving around the world when it really isn't.

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So inside of you're going to say return an object and I'm going to give this all the properties that

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a normal location reading off a device would have.

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We haven't really looked at what these different readings are but we will see them very quickly.

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So first off I can give this thing a timestamp.

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The timestamp can be any value which just has to be a number.

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So I'm going to put in like 1 0 0 like so and then going to give it a coords property inside of here.

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I'm gonna give it a speed of 0 a heading of zero an accuracy of 5 an altitude accuracy of 5 an altitude

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of 5 and then here are the two that actually make her actually important for us we're going to do a

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longitude of negative 120 2 0 3 1 2 1 8 6 and we're going to add on increment times 10 meters with degrees

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and then 4 latitude we're gonna put in 3 7 3 3 2 3 3 1 4 1 increment times 10 meters with degrees now

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the latitude and longitude that I just entered in here our fourth Apple headquarters once again in Cupertino.

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So essentially we're going to start off our fake location tracking at Apple headquarters and then over

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time we're going to add in just like 10 meters 10 meters 10 meters just kind of move the user around

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the location or around the world.

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All right.

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Finally down at the very bottom this is where the real magic happens.

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We're going to define a counter variable and set it to zero.

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And we're going to set up a set interval function and I'm going to run this interval function once every

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second.

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So I'll put in 1000 milliseconds right there.

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So now inside of here this is where we're going to really trick out Expo location.

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We're going to say location dots event emitter dot emit.

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We're going to do Expo dot location changed.

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We're gonna pass in an object as a second argument.

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We're going to say watch I.D. is location dot underscore get current watch I.D. and then location is

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our get location function and we're going to pass in that counter and then after we emit that event

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I'm going to do a counter plus plus like so.

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All right.

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I know that's a lot of typing but now we can really see exactly what's going on here.

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So whenever we import this file into our project once every second we're going to emit an event directly

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into the location library and we're essentially faking out as though the user's location has changed

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in the real world the watch idea right here is just little bit of background code.

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What's more important is location location right there that's going to have our fake location that is

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going to be changing once every second over time.

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So once every second we're going to get a changed land longitude and latitude by 10 meters.

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So this is going to allow us to very easily test out all of our tracking code and actually make sure

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that hey our application works on the user's location is changing over time.

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And once again this is only for testing purposes.

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So if we ever deploy our application we would want to make sure that we do not import this file into

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our project.

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So now that we've got this Together blessing I'm going to do is go back over to my track and create

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screen and at the very top I'm going to add in an import for up one directory underscore mock location

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like so.

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Now in theory once every second we are triggering a new change in location inside of our app.

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Now I do want you to know that as we start to test this you are going to initially start to see the

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user's location on this map right here like jump around.

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And the reason for that is that it's going to eventually conflict with the actual reading of where your

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user is.

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But we'll see that in action in just a moment.

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OK.

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So now we've got this put together.

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We've got some test code right here.

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We can now start to actually write out our tracking stuff back inside of a check create screen.

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So let's take care of that in the next video.