Pro Android with Kotlin

Figure 1-3
AVD Manager

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6
CHAPTER 1: System
Handling running virtual devices can also be done by various command-line tools; see 
Chapter 
18
 for more information.
The SDK
The software development kit (SDK) is, in contrast to Android Studio, a loosely coupled 
selection of tools that are either essential for Android development and as such directly 
used by Android Studio or at least helpful for a couple of development tasks. They can all be 
started from within a shell and come with or without their own GUI.
In case you don’t know where the SDK was installed during the installation of Android 
Studio, you can easily ask Android Studio: select 
File 
➤
 Project Structure 
➤
 SDK location
from the menu.
The command-line tools that are part of the SDK are described in Chapter 
18
.
Caution
Virtual devices do not emulate all hardware supported by real devices. Namely, in the 
first quarter of 2018, the following are not supported:
 
WiFi before API level 25
 
Bluetooth
 
NFC
 
SD card eject and insert
 
Headphones attached to the device
 
USB
You must thus take precautions inside your app for these not to be present if you want to use the 
emulator.

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7
© Peter Späth 2018 
P. Späth, 
Pro Android with Kotlin
, 
https://doi.org/10.1007/978-1-4842-3820-2_2
Chapter
2
Application
An Android app consists of components such as 
activities
, 
services
, 
broadcast receivers
, 
and 
content providers
, as shown in Figure 
2-1
. Activities are for interacting with device 
users, services are for program parts that run without a dedicated user interface, broadcast 
receivers listen for standardized messages from other apps and components, and content 
providers allow other apps and components to access a certain amount and kind of data 
provided by a component.
Figure 2-1.
An app in the Android OS
Components get started by the 
Android Runtime
, or execution engine if you like, either 
by itself or on behalf of other components that create start triggers. When a component 
gets started depends on its type and the meta-information given to it. At the end of the 
lifecycle, all running components are subject to removal from the process execution list 
either because they have finished their work or because the Android OS has decided that 

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