Mobile App user interfaces have come a long way from the early days, and while users have more devices to choose from than ever, they all expect consistently high-quality experiences from their apps. Apps are expected to run fast and the user interfaces are expected to be smooth; all this while running on a massive array of devices of varied capabilities. Your app needs to run on devices with screens as big as televisions on the one end of the scale, and smartwatches with screens as small as 2.5 cm or even smaller on the other end of the scale. At first glance, this may seem like a nightmare, but there are simple tricks to make building responsive Android apps easy.

In this book, you'll learn a diverse set of skills as well as some theoretical knowledge that you can apply to build fast, responsive, and great-looking Android applications. You'll learn how to go about designing the screens that your application will actually need, and then how to build them for maximum flexibility and performance while keeping your code easy to read and avoiding bugs.

In this chapter, we will look at the basic principles used to build user interfaces for Android applications. You'll need to be familiar with concepts to build even the simplest Android application, so in this chapter, we'll cover the following topics: