Android Fundamentals

• kotlin java and c++ are used to write c++ programs.
• android is multi user linux os syste, it means each app treated as different user.
• each app created has it’s own unique id.
• least privilege means when each application can access only it’s own components and no further.
• two apps can share the same user id, and run on same virtual machine..
• if user want privilege to access devices such as camera, location etc.. it should request to do so.

App components

• compoenents are building block of android application.
• there are four types of components.
  • Activities
  • Services
  • Broadcast receivers
  • Content providers

Activities

• activities are interface with entry point that interact with user.
• activity can be like read list od data., it can also be doing some other task like for example creating data.
• together they form the application.
• to do app example :
  • activity to show todos.
  • activity to add todo.
  • activity to remove todo.
  • together they make todo application.

Services

• entry point for keeping an app running in the background.
• service does not provide a user interface, which means it might run something in the background while user doing something else.
• service might fetch data over the network

Broadcast receivers

• component that enables the system to deliver events to the app outside of a regular user flow.
• broadcast receivers are another well-defined entry into the app.

Content providers

• it manage a shared set of app data that you can store in the file system.

Activating components

• activities, services, and broadcast receivers are activated by an asynchronous message called an intent.
• Intents bind components to each other at runtime.
• Intent object create a message to activate a component or a specific type of component.
• activity and service define the action to do.
• content providers are not activated by intents.
• they are activated when targeted by a request from a ContentResolver.

The manifest file

• android system know if component file exit from manfiest file when system read it.
• app must declare all its components in this file.
• things manifest does in addition to declaring the app’s components:
  • Identifies user permissions the app require.
  • Declares the minimum API Level required by the app.
  • Declares hardware and software features used or required by the app such as camera.
  • Declares API libraries the app needs to be linked against.