All language subtitles for 2. Getting Location Data From Across Platforms

To get started with the weather app go to the GitHub repository listed in the course resources. Then
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clone the repository and open the project from Android Studio,
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just as we've done with the previous apps.
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Finally remember to click on get dependencies
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after the project is open so that all your errors go away and your project builds successfully.
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Then we should see that we have a number of folders inside our lib folder. So I've classified all of
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our different files into different sections.
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We've got our different screens and we've got three of those:
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a loading screen, a location screen and a screen for getting the weather based on the city name.
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And then we've got some services such as the location.dart or the networking part or the weather
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part. And we finally got some utilities which currently just have a constants file. And everything starts
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out from the main.dart file.
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So go ahead and have a look at the designs that we've already created for you.
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But essentially the UI is kept pretty simple because we're going to be doing a lot of backend stuff
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and networking.
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So we've kept the user interface relatively easy to understand, even the most complex screen which is
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the location screen is pretty simple if you just read through it.
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It's simply a container with a background image with a column inside that contains a number of buttons
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as well as some text widgets.
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So it's pretty simple stuff
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so far. Now the first thing that happens when our app loads is it will load up the loading screen as the
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first route.
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So inside our loading screen, you can see that there's pretty much nothing in here other than a state-
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ful widget that contains a single raised button which says get location.
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So if you run this as it is, there's nothing terribly exciting going on right now,
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it's just a black screen with a single button. But this is where our app is going to start from and the
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first thing that we want to do is to be able to grab the user's location when we tap on this button
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get location.
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Now in order to do this, we're going to leverage the power of Flutter packages. And there's a package
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called geolocator that we're going to be using to be able to get location services both from iOS
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and Android. So we'll have to call a single line of code like this that they've described in the documentation
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and the package will go behind the scenes and do all the necessary things to be able to get us the location
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whether if our code is being run on iOS or Android.
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So let's get started by adding this as a dependency.
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So I'm just going to copy this and go into my pubspec.yaml
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and right over here just below our cupertino_icons,
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I'm going to add our geolocator and make sure that it's formatted to be at the same level as cupertino
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icons.
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And at the moment it's coming in as a string, I'm just going to delete it.
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It doesn't really matter if you keep it or not.
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It will be interpreted in the same way.
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But I like to have things consistent.
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So now that we've added that dependency, let's click on packages get to actually imported into our project.
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And once that's complete, we should be able to see it inside our external libraries and Flutter plugins.
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So you can see geolocator right there.
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So now we can actually use it and we're going to be using it inside our loading screen for now.
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So the first step towards using any of these packages is of course importing it.
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So right at the top, we're going to import our geolocator.
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There it is, geolocator.dart.
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And now we're going to create a new method which is not going to return anything, but all it's going
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to do is it's going to get the location, so get location. And inside the curly braces of this method,
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it's going to do everything that's necessary to be able to bring us the current user location.
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So if we take a look at the docs, it tells us to query the current location of the device.
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Simply make a call to the getCurrentPosition method.
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And it shows us how we do this.
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So it's data type position and this is something called position. And then we have a keyword called a
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await, and we use the geolocator to get the current position.
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And as an input we specify how accurate we want that location to be.
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So let's go ahead and copy this line of code into our project and I'm going to paste it right inside
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this new method I created called getLocation.
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Now the first thing that we have to do in order to make this actually work is to add a modifier keyword
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to this function and it's going to be the word async.
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Now what exactly is this async and await?
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Well this is a way for us to be able to carry out time consuming tasks such as getting the GPS location
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from the phone. You can imagine that asking the phone for the current location, getting it back then processing
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it and finally being able to have access to it takes a little bit of time.
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And there's also other things such as trying to get data downloaded from the Internet or trying to read
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something from file.
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These are all things that can take an unpredictable amount of time but also it can take quite a long
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time. By using asynchronous programming
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we can get these time consuming tasks to happen in the background instead of happening in the foreground
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and blocking up our UI and freezing up our app.
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Now the entire next lesson is dedicated to asynchronous programming in Dart and we'll talk about async
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await futures and all that in a lot of detail.
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But for now let's try and get the current location first.
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So we've got this object called Geolocator which comes from the geolocator package and we're going
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to use it to get the current position by providing a desired amount of accuracy.
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And I'm going to change that from high to low. And you can see that there's a whole bunch of different
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options you have, lowest, medium, low, high best for navigation and the thing to remember is that the more
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accurate the location you're trying to get, the more battery intensive it will be.
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So if you want to be kind to your users and their phones battery, only use as much accuracy as you need.
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So if you're making a navigation app where people actually need
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turn by turn directions, then you probably do need to choose something that is quite accurate like best
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for navigation.
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But if we're only trying to get the weather, then something like low which gives us the accuracy to the
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nearest kilometer on iOA and nearest 500 meters on Android, is probably good enough. And even the lowest
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one is probably fine, but either way choose one of these accuracy levels.
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And now we should hopefully be able to get our position back and once we do get our position back, I'm
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simply going to print it into the console to see where we currently are
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according to the GPS. Now there's just one more step that you have to do for this to work and that
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is to ask the user for permission to get their current location because you don't want apps that just
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happens at the user's location without them knowing cause that's kind of dangerous. And both on iOS and
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Android,
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you have to explicitly request positional data.
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So let's see how we can do that. In the documentation for geolocator, if you scroll down a little bit
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they'll tell you that in order to get permissions on Android you need to add either the access coarse
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location or the access fine location into the Android manifest,
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so where we're only using a low level accuracy positional data, so we only need permission to get coarse location.
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So let's go ahead and hit copy on this particular tag and let's go into our Android project folder right
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here and then go into our app folder, our source, main
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and here we should find our AndroidManifest.xml file.
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So if you double click on this to open it up you can see that these are various settings we have set
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for our Android project.
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And it tells us that we have to add one of the following two lines as direct children of the manifest
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tag.
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So what does that mean?
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Well this is the manifest tag and it's the highest level tag in this particular file.
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Everything in it are its children but there's also lower hierarchy such as the application tag or the
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activity tag or the meta data tag.
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And if you've ever worked with HTML, then this formatting will be very familiar to you because it's
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styled in XML which stands for extensible markup language.
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And essentially it's kind of the same as our key value pairs where the key are in these tags and the
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values are held inside the tags.
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So inside the manifest tag,
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so right here just after the closing angle bracket, we're going to paste in our user's permission tag.
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And this one tells our Android app that we need to access the coarse location and it should request
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it from the user.
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So that's our Android part done, so we can close up our Android folder.
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And now we have to ask for permission on iOS,
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so when an iOS user uses our app. And what we have to do is we're going to copy these two lines, a key
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and a string, which tells the user why we need to use their location.
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So you can change this text if you wish to,
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if you want to make it more descriptive for the user when you're actually requesting for their data.
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But let's copy these two lines and we're going to add it to our info.plist file.
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So now we have to go into our iOS folder and inside our runner folder are all the files that are specifically
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related to our iOS app.
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And here you should find a file called info.plist.
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So if you double click on that you can see again this is an XML file and we're going to add the key
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and the string to this file just below where it says dict or dictionary.
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So we're going to pay those two lines in and now we have a dictionary of a key and a value pair.
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So this tells our iOS app that when we request for the user location, this is the description that we're
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going to give the user to tell them why we need their location.
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Now let's hit save.
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Let's close down those two files.
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And the last thing we have to do is to actually call this method, get location. And we're going to call
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it when the user presses on that button that says get location,
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so right here in the onPressed. And in here I'm going to call get location and now we're ready to test
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our app.
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And before you test it, I recommend just stopping the current app from running and then starting it from
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cold because we added in our dependencies and we messed around with the Android manifest and the iOS
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plist.
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It's usually a good idea
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once you've done that to just start it from scratch. It takes a little bit longer but there's a lot of
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things that has to link up behind the scenes.
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So now that our app is up and running when I click on this button get location, it should call that get
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location method
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I created this now and it should fetch our current position and print it out into the console.
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But the first thing it will do when I click on the button is to ask me for permission to give it my
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current location.
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So make sure that you click allow at this step. And now it should print out my latitude and longitude
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into the console. Now where does that location come from?
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Well if you're using a simulator, it usually comes from a default location that set to the Apple headquarters,
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so somewhere in cupertino. If you're running your app on Android then you can click on these three dots
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right at the bottom here.
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And this gets you into the extended controls and you can select on the location tab to set the latitude
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and longitude
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you want this phone to report from.
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You can manually set and send the location data to your app.
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Now at this point, it's worth mentioning that if you are running your phone on Android and you're seeing
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some errors in the console relating to something about Android X, then be sure to head into the course
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resources where there's a link to this resource on the Flutter documentation talking about how to make
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your app AndroidX compatible.
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Now this issue won't affect everybody.
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It's only if your app actually crashes and it refuses to build.
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So that was how easy it is to actually get the current GPS location.
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And if you think about it, behind the scenes a lot of things had to happen.
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The iOS counterpart had to talk to the iOS operating system to be able to get the location from that
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device and the Android part had to talk to the Android OS and get the location in a completely different
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way.
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But we were able to do that by simply using the geolocator package which has taken care of all of that
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for us. And we didn't really have to do anything other than simply add it into our project.
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And if you're curious how geolocator manages to do this then you can head into the external libraries
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folder and go into your Flutter plugins and expand the geolocator library.
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Now here you'll see an iOS and an Android project.
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If you expand the iOS project and go into the classes, you can see that there's a whole bunch of files
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in here that are written in Swift to work with the iOS location API to be able to grab the location
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data and to be able to return it to you.
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Now similarly if you have a look inside the Android folder and you go into src.main and then
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go into the Java folder, there's both a data folder and a task and a utils folder.
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And it's here where there's all this Java code that's been written to be it to deal with the Android
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location manager and to be able to fetch that location data for you.
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Now you can imagine writing all of this Java code and all of this Swift code not only takes a lot of
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expertise but also takes a lot of time. But because the author of this plugin has very kindly packaged
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it into a really simple to use plugin, we're able to piggyback on all of that hard work simply by importing
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it and calling just one line of code.
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And hopefully when you build some custom functionality that you think other people might find helpful
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you'll also create a package around it so that you can share it with other Flutter developers and pay
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it forward.
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But for now, I want to focus on these two keywords that we've never seen before, async and await. In order
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to understand this we have to learn all about synchronous and asynchronous programming.
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So we have to understand what's actually going on here in this code.
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head over to the next lesson and let's learn all about asynchronous programming.