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All right.
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So now that our app is actually pretty much fully functional, other than the fact that we still don't
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have the location data and we can't get the weather for the current location.
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So that's what we're going to tackle in this lesson.
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Now, the first thing we need to do to be able to get hold of the location data is to import a package
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that Apple has created called CoreLocation.
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And this comes with something called a location manager.
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So we can create a locationManager here and it's going to be created from 
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the CLLocationManager class.
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And this object that we've created, our locationManager is going to be responsible for getting hold
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of the current GPS location of the phone.
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But before we can use it though, the first thing we have to do is we have to trigger a permission request.
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So we're going to say requestWhenInUseAuthorization. Because the user's location is a really private
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piece of data,
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you don't want apps to just know exactly where you are without having to ask for explicit permission.
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So when we call this locationManager.requestWhenInuseAuthorization method,
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wow, what a mouthful,
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then it will show a pop up on screen that asks the user for permission.
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But in addition to calling this method, we also have to go into the info.plist, which is the property
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list where we've got a bunch of key-value pairs that determine some of the basic settings of our app.
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And here, we're going to add a new property.
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And if you scroll down in this list, you should be able to find one that says, "Privacy - Location When in
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Use Usage Description.
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And for this key, we're going to give a value that's going to be the message that we're going to tell
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the user why we need their location.
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So, we'll say, "We need your location to get the current weather for where you are."
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So, now that we've got a Privacy - Location When in Use Usage Description, we can now head back and run our
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app.
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And as soon as the WeatherViewController loads up, you should see a pop up which is in black
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if you're in dark mode, like I am, or in white if you are not in dark mode. And it'll ask you, "Do you want
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to allow 'Clima' to access your location?"
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And then here is that little string that we added earlier on in our plist,
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"We need your location to get the current weather for where you are."
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So make sure that while you're testing, you always click on Allow because, otherwise, you're going to have
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to dig into the settings, the privacy and location settings, to allow the Clima app to access the location.
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So now that we've gotten permission from the user to get their location, well, then the next step is to
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use the locationManager to request location, and this method "Request for a one-time delivery of the
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user's current location."
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And because we're building a weather app here where we don't need to track where the user is or where
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their car is,
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so if you were building a navigation app or a fitness app where you needed the turn by turn location
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data the entire time that they're using the app, then you might want to use something called 
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startUpdatingLocation instead
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and this basically monitors their location and constantly reports back when it updates. But in our case,
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the request location is sufficient.
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But how do we actually get hold of that location once the location manager has found it?
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Well, notice how requests location doesn't return anything.
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In fact, the only way to get a hold of it is through the locationManager(_:didUpdateLocations:) method.
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And this is what the locationManager is going to call once it finds the location. So given now that
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you know what the delegate method is that you need to implement and you know all about protocols and
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delegates, here's a challenge for you.
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See if you can implement the required protocols and simply be able to print got location when the
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locationManager triggers the didUpdateLocationsDelegate
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method. Also, try to use a Swift extension to split out the didUpdateLocation method from
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the WeatherViewController.
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Now, printing out got location can actually be a little bit harder than it sounds.
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Make sure you have a read of the documentation to figure out how to do this successfully.
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So pause the video and see if you can complete this challenge.
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All right.
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So firstly, we know that this method, once it gets hold of the location, is going to trigger this delegate
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method.
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And this delegate method if we click on it, shows us that it comes from the protocol 
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CLLocationManagerDelegate.
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So we have to adopt this delegate protocol in our WeatherViewController if we want to be able to assign
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ourselves as the delegate for the locationManager to be notified of that location update.
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So we can either add our CLLocationManagerDelegate here, alternatively, as we saw in the last lesson.
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We could simply create a brand-new extension down here which extends our WeatherViewController.
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And here, we can add our CLLocationManagerDelegate, so that we split out this part of the functionality
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of our WeatherViewController and we can mark it out with MARK comment, and we can call this 
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the
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CLLocationManagerDelegate.
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So you'll often see that people will split out their view controllers with sections that are named based
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on the delegate protocols that they are adopting.
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So this action is obviously related to the location manager, and the delegate method was called 
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didUpdateLocations, location manager did update locations.
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So if we hit enter, that should enter that method for us.
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Now, you have to remember that in order to actually get the notification for this, we have to set our
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WeatherViewController,
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so this current class, as the delegate for the locationManager. Without this property set, nothing is
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going to happen even if you adopt the protocols and have the delegate methods.
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So, now that everything is all set, we can simply print "Got location data" and then go ahead and hit run.
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And at this point, your app will crash.
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And if you scroll right to the top, you'll see that you have an error saying, "Terminating apps," so your app
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crashed, "because of a reason the delegate must respond to locationManager:didUpdateLocations."
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And you're wondering, "Hey, wait a minute. I did actually respond to locationManager:didUpdateLocation. 
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It's right here.
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What's going on?
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Well, the reason is because we have to set the current class as the delegate to be able to register with
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the locationManager and to be able to respond when requestLocation actually triggers this method.
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So what you'll find is that if you have the locationManager.delegate = self set after you
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trigger this method, you're going to end up crashing your app.
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Now, in addition, if you take a look at the quick docs for request location, it says right at the bottom:
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"When using this method, the associated delegate must implement the didUpdateLocation and 
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didFailWithError methods.
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Failure to do so is a programmer error."
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So in addition to having this locationManager, didUpdateLocationsDelegate method implemented,
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we also must make sure that we have our locationManager didFailWithErrorMethod implemented.
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And in this method, all I'm gonna do is just print the error
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if there were any.
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And that's the solution to the challenge.
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The trick of this challenge was to make sure that you set the WeatherViewController as the delegate
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before requesting the location and also to make sure you've implemented the required didFailWithErrorDelegate
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method.
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So, now if we run our app,
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then you should see "Got location" printed in the console because the locationManager has found the location
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and they are triggering this method.
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But where's the permission request?
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Where's the pop up?
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Because we've already agreed to share our location to this app,
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we don't get that pop up ever again.
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We only see it once. And once you've agreed to it, then you don't need to touch it anymore.
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If you ever need to change it, then you can go into the settings of the simulator or your phone privacy
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location services. And here under your app Clima, you can see "Never," "Ask Next Time," or what we've agreed
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to at the moment "While using the app." So what if instead of printing "Got location data," we can actually
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print out the actual location of where our simulator is located,
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terms of the longitude and latitude.
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How would we do that?
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Well, notice how when the locationManager calls this method, it also passes in this "locations" input.
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And this is an array of CLLocations. We can get hold of the last location that they added in there.
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So we'll just call it location and we'll set it to equal locations.last.
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So that's the last item in the array.
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And generally, the locationManager will try to get the current GPS location and hone in on a relatively
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accurate version of it,
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so you might end up with several locations. By fetching the last location,
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we should be able to get the most accurate one. But because this locations.last is an optional,
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in order to use it, we should first optionally bind it to a new constant called location, so that we unwrap
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it. And then within this block, we can create a latitude which will set to equal to location.coordinate.latitude,
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and then we can create a longitude which is going to be the location.coordinates.longitude.
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-
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And now let's try and print out those values: the lat and lon.
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So let's hit run and see what happens.
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And there it is.
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I can see my current location which is London and I've got a latitude of 51.5, 
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a longitude of -0.1.
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Now, you might be wondering, how are you getting a location data for the simulator?
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Well, if you're going to debug, there's a section called Location. And here you can set a location for the simulator.
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I've set mine to Custom Location and added the coordinates for London.
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You can also change the simulators location, say, to Apple's headquarters.
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However, the simulator doesn't always pick up the location change right away.
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And in order for that to go through, you also have to head over to Home. and go ahead and delete that
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Clima app. In order to run it again, and it will now report the updated latitude and longitude.
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And if you want to test this, you can also set a custom location with a custom latitude and longitude
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as well.
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But again, you'll have to go through the process of deleting the app and rerunning it again.
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So, now that we've got a latitude and longitude, if we head over to the OpenWeather Map API Docs,
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you can see that in order to get the current weather data, we can either go by city name or we can also go
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by geographic coordinates which is what we've got at the moment.
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And the way to make that API call is using the same URL as what we used previously.
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But then at the end, we tag on two parameters: a lot and a lon.
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And notice how the lon is spelled a little bit 
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weirdly. it's L-O-N, rather than L-O-N-G.
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So in order for our API call to work, we have to be able to match their parameter names.
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Let's first test it out in the browser.
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Let's go ahead and go into our WeatherManager and get hold of our weatherURL with our app ID,
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and our units already set, and then I'm going to paste it into the browser bar, and then I'm going
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to add another parameter by adding the ampersand symbol, and the first one was called lats will set lat
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equal to, let's say, 51, which is roughly around where I am.
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And then let's add another one with the ampersand and this is going to be lon with L-O-N,
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and this is gonna be equal to -0.1 which is going to be roughly around London.
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So now if we hit Enter, you can see that we're getting our data back.
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It's clear skies with a temperature of 19.4.
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Perfect.
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Now that it's working, let's try and figure out how we can form this URL string in our code.
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So down here, we've already got a fetchWeather method that takes a cityName and creates a
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urlString from it. And then performs the request with that urlString which goes into this method
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and does the networking using URLSession to fetch some data back from OpenWeather Map. And then
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we parse the data, and then we create a weather object to pass back to our delegate.
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So this part is actually completely reusable.
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It's exactly the same process.
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So all that we need is another fetchWeather method.
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So if we go into our WeatherViewController, and right where we get back our latitude and longitude,
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so I'm going to delete those two print statements, 
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instead, I'm gonna call my weatherManager and I'm going to get it to fetchWeather, but instead of using 
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a cityName parameter, I want to be able to use the latitude parameter and put in the lat constants that I've
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just got,
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and then the longitude, which is going to have the long property. And I want to be able to call this method
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in order to get some weather data. And when this goes through successfully and I actually manage to get
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the data, then the data is going to come back inside my didUpdateWeatherDelegate method. And it's
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here where it's going to update our temperatureLabel and conditionImageView without any extra code
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on our part.
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So this is a time for your challenge.
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The challenge is to make this method work and get rid of all of the errors. Write the method 
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fetchWeather with latitude and longitude in the WeatherManager, so that when you run the app, it actually gets the
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weather for your current location.
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So pause the video and try that now.
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All right.
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So let's go ahead and copy this method and we're going to implement it in our WeatherManager.
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So down here, I'm going to create another function called fetchWeather. And Swift is totally cool with
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methods which have the same name as long as they have different parameter names.
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So this fetchWeather method is going to have the latitude and longitude parameter names and it's going
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to take two pieces of data.
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Now, how can we figure out what data type we are going to send over?
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Well, if we head back to our WeatherViewController and we hold down option and click on latitude or
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longitude, then you can see the data type of the latitude and longitude.
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It's something called Core Location LocationDegrees.
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So CLLocationDegrees.
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So let's go back to our WeatherManager and assign that as the data type that we're expecting,
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CLLocationDegrees for the latitude and CLLlocationDegrees for the longitude.
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And once we get hold of the latitude and longitude, what we're going to do is we're going to create a
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URLString, and it's going to be equal to an interpolated string that's created the first part being
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the weatherURL, and then at the end, we're going to tag on the property lat which is going to
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equal latitude that we got passed in.
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And then the second property that we need to add is the lon, and remember to check that you've spelled
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it exactly the same as what I've got here,
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L-O-N and L-A-T.
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This is a really common place where students fall down. And then we're going to set it equal to, making
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sure that there's no spaces anywhere the longitude that got passed over from our location manager.
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Now that we're done with our urlString, all we have to do is trigger performRequest with
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our urlString. And it will go through the same process as it did before with the cityName to network
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and pass the data, and then trigger our delegate method didUpdateWeather which will update our temperatureLabel
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and our conditionImageView.
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So let's hit run and see this in action
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So you saw it immediately update with the location-based temperature and condition.
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And now if I go ahead and type a city, say, Paris, you can see that in Paris, it's thunderstorms. That also
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works. But how do we get back to our location-based weather? And how can we update our cityLabel to be
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able to tell us which city we're currently in when we're getting our location data? And I want to pose
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this as a challenge to you.
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Can you write the last part of the app on your own? Link of the button in the top left, so that when it
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gets pressed, we get the weather for the current location displayed. Also, the label should update to show
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the name of the current location. On the other hand, when we type in a cityName, we get the weather for
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that location and the label will display the name we get back from OpenWeather Map. Linking up the button
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will be the tricky part. So check the documentation in Stack Overflow
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to figure this out. I'll give you a few seconds to pause video before I show you the solution.
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All right.
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Here's the solution.
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Let's tackle updating the cityLabels first.
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Now, if we take a look at the data that we get back from OpenWeather Map, you can see that right at the
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bottom, we get the name of the location based on the latitude and longitude.
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So if I go ahead and update my latitude and longitude to my current location, then you can see that it's
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telling me that I'm currently inside the city of London.
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So we've already managed to get hold of that name property here.
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All we need to do is inside our WeatherViewController where we're updating our labels, we should go
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ahead and set the self.cityLabel.text to equal the weather.cityName property. So now
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that should populate our citylabel.
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Let's give it a run, see if that works.
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And as you can see that the label is now updating using the location name from the JSON that we got
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from OpenWeather Map.
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At the moment, I still got my simulator set to Cupertino.
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Let me change the simulator back to London using the custom coordinates.
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And now if I simply just quit the simulator and then rerun the app, you can see that it's now updated
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to use that current location.
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So switching different location types in the simulator can be quite painful. But hopefully, if you're
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running this on a physical device, you'll actually be getting your exact current location. So, now all
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that's left is to be able to switch back to location mode when we have gone to the city mode.
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So right now I've got my weather for Paris and I want to be able to click on this button to go back
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to my current location's weather.
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So in order to do that, the first thing we need to do is to create an IBAction.
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Here let's create an IBAction that links this button down into our WeatherViewontroller
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and I'm going to call this action locationPressed, and then change the data type into UIButton.
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And now I've got my IBAction locationPressed where I can change my app to, again, 
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use the locationManager's location to get the weather. But how do I trigger this
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locationManager, didUpdateLocations method again?
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Well, one way of doing it would be to call this requestLocation method again.
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But if we've already requested the location and we haven't changed our GPS location, then if there's
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no change, then there's gonna be no update.
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So this method is not going to get called.
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And you can confirm this by simply adding a print statement inside the locationManager.
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So the way to solve this is we want to be able to call locationManager.requestLocation and trigger
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a reupdate and call this method again so that we fetch the weather.
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But in order for this to work, once we've gotten hold of the weather, either at the time when we've loaded
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up our app or at the time where they press the location button, we want to be able to stop the 
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locationManager.
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So we're gonna say locationManager.stopUpdatingLocation as soon as it's gotten hold of a location.
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So now the sequence of events is, first, we set our locationManagersDelegate as ourself, then we call
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requestLocation, locationManager is gonna be hard at work fetching the current location.
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And once it does, it calls this method passing in the locations that it's found, and we look inside that
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array to find a location.
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And as soon as we found one, then we tell the locationManager to stop and we use the location to get
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the current weather.
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So at a later point, if we press on the locationPressed button, then it calls this method again.
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And now our locationManager has been activated once more, so we can call this delegate method again.
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Let's give that a go and see if it works.
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The first thing that we see is the current location's weather. And now I'm going to search for another
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location's weather, see what it's like in Beijing. And now if I want to switch back to location mode,
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I press on this button and I trigger the request location once more where the locationManager calls
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didUpdateLocation and I fetch the weather again.
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So that's it.
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We've managed to create our weather app that uses the current location to get weather, as well as using
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the city name that the user types in through the text field. And in the process, we've learned about text
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field, protocols and delegates, extensions, networking with URL session, as well as parsing JSON data.
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So it's been a pretty jam-packed module if you ask me. And it might be that you might have to review
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certain parts of this module over the coming days to be able to really digest it and make it your own.
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But once you've done that, head over to the next lesson and there'll be a challenge, as usual, for you.
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And I'll see you on the next module.