Before we explore any of the code and learn our first bit of Kotlin, you might be surprised to learn that we can already run our project. It will be a fairly featureless screen, but as we will be running the app as often as possible to check our progress, let's see how to do that now. You have three options:
Run the app on the emulator on your PC (part of Android Studio) in debug mode
Run the app on a real Android device in USB debugging mode
Export the app as a full Android project that can be uploaded to the Play Store
The first option (debug mode) is the easiest to set up, because we did it as part of setting up Android Studio. If you have a powerful PC, you will hardly see the difference between the emulator and a real device. However, screen touches are emulated by mouse clicks, and proper testing of the user experience is not possible in some of the later apps, such as the drawing app. Furthermore, you might just prefer to test out your creations on a real device – I know I do.
The second option, using a real device, has a couple of additional steps, but, once set up, is as good as option one, and the screen touches are for real.
The final option takes about five minutes (at least) to prepare, and then you need to manually put the created package onto a real device and install it (every time you make a change to the code).
The best way is probably to use the emulator to quickly test and debug minor increments in your code, and then use the USB debugging mode on a real device fairly regularly to make sure things are still as expected. Only occasionally will you want to export an actual deployable package.
Note
If you have an especially slow PC or a particularly aging Android device, you will be fine just running the projects in this book using just one option or the other. Note that a slow Android phone will probably be OK and cope, but a very slow PC will probably not handle the emulator running some of the later apps, and you will benefit from running them on your phone/tablet.
For these reasons, I will now go through how to run the app using the emulator and USB debugging on a real device.
Follow these simple steps to run the app on the default Android emulator:
On the Android Studio main menu bar, select Tools | AVD Manager. AVD stands for Android Virtual Device (an emulator). You will see the following window:
Notice that there is an emulator in the list. In my case, it is Pixel 2 XL API 28. If you are following this sometime in the future, it will be a different emulator that was installed by default. It won't matter. Click the green play icon (to the right) shown in the following screenshot, and wait while the emulator boots up:
Now you can click the play icon on the Android Studio quick-launch bar as shown in the following screenshot and, when prompted, choose Pixel 2 XL API 28 (or whatever your emulator is called) and the app will launch on the emulator:
You're done. Here is what the app looks like so far in the emulator. Remember that you might (probably do) have a different emulator, which is fine:
Clearly, we have more work to do before we move to Silicon Valley and look for financial backing, but it is a good start.
We need to test and debug our apps often throughout development to check for any errors, crashes, or anything else unintended.
Note
We will see how we get errors and other feedback for debugging from our apps in the next chapter.
It is also important to make sure it looks good and runs correctly on every device type/size that you want to target. Obviously, we do not own one of each of the many thousands of Android devices. This is where emulators come in.
Emulators, however, are sometimes a bit slow and cumbersome, although they have improved a lot recently. If we want to get a genuine feel for the experience our user will get, then you can't beat deploying to a real device. So, we will want to use both real devices and emulators while developing our apps.
Note
If you are planning on using the emulator again soon, leave it running to avoid having to wait for it to start again.
If you want to try out your app on a tablet, you're going to need a different emulator.
Note
Creating a new emulator
It is simple to create an emulator for a different Android device. From the main menu, select Tools | AVD Manager. In the AVD Manager window, left-click Create New Virtual Device. Now left-click on the type of device you want to create – TV, Phone, Wear OS, or Tablet. Now simply left-click Next and follow the instructions to create your new AVD. Next time you run your app, the new AVD will appear as an option to run the app on.
Now we can look at how we can get our app onto a real device.
The first thing to do is to visit your device manufacturer's website and obtain and install any drivers that are needed for your device and operating system.
The next few steps will set up the Android device for debugging. Note that different manufacturers structure the menu options slightly differently to others. But the following sequence is probably very close, if not exact, for enabling debugging on most devices:
Tap the Settings menu option or the Settings app on your phone/tablet.
This next step will vary slightly for different versions of Android. The Developer options menu is hidden away so as not to trouble regular users. You must perform a slightly odd task to unlock the menu option. Tap the About device or About Phone option. Find the Build Number option and repeatedly tap it until you get a message informing you that You are now a developer!
Go back to the Settings menu.
Tap Developer options.
Tap the checkbox for USB Debugging.
Connect your Android device to the USB port of your computer.
Click the play icon from the Android Studio toolbar, as shown in the following screenshot:
When prompted, click OK to run the app on your chosen device.
We are now ready to learn some Kotlin and add our own Kotlin code to the Hello World project.