Android is an open source mobile platform launched by Google in 2008 and ever-since it became the favourite for people and developers around the world. Android is Linux based multiprocess and multithreaded OS. Google’s Android OS is not limited to phones but you can use it to build a DVR, a handheld GPS, an MP3 player etc.
Although Android platform is an open source and customizable, Android users and developers have become habitual to the constructs developed by Google for Android devices. The use of these Android concepts is vital for developing an application quickly. GHD Sports
Key Concepts of Android are:-
Apps and APK Files
Views and ViewGroups
Layout XML Files
I am giving you an overview of the Android key concepts. After having a basic understanding of Android’s key concepts you can go deeper into the various different topics.
Apps and APK Files
An Android app is an Android Application. An app is packaged in an APK file i.e. Android application package. The APK file contains the compiled Java code and other resources like images and texts for the Android application
An Android activity is a GUI component. You can understand it as a window in a desktop application. As mobile phone screens are small, an activity takes up the whole screen. If you open multiple activities then they are stacked on top of each other. You cannot arrange activities side by side like you can do with desktop windows.
Activities are unique, focused actions which a user can take. As it is difficult to scroll, zoom in or click links on a small screen hence it is recommended that an app display only one activity per screen. This will present the most relevant information to the user and allows them to launch a new screen for additional information or click the back button to view the previous activity. The screen can expose multiple tasks but it should help the user complete just one activity at a time.
In Android, a fragment is a fragment of a total user interface. A fragment only takes up part of the screen. Fragments are used in the activities. Fragments can also be used within different activities. Fragments contain Views and ViewGroups inside them.
View and ViewGroups
Android GUI elements come into three categories i.e. Activities, Views and ViewGroups. Activities are the windows/screens. Views are the individual GUI elements, like a TextView which displays a text, a Button that users can click on etc. ViewGroups are containers for Views. A ViewGroup actually groups a collection of Views together. Views and ViewGroups can be nested inside an activity or inside even a fragment which is nested inside an activity.