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Android Classes and Basics

Setting Up an Android Virtual Device (AVD)​

  • Open the AVD Manager dialog via Window → Android Virtual Device Manager and press the New button.
  • Enter the values similar to the following screenshot.
  • Afterwards press the OK button.

Creating an Android App​

  • To create a new Android project select File → New → Other → Android → Android Project or File → New → Android Application Project from the menu.
  • Fill up the data similar to below screen shot.
  • Press the Next button and ensure that you have selected to create a launcher icon and an activity.
  • On the wizard page for the launcher icon, create a nice looking icon.
  • Press the Next button and select on the next page the Blank Activity template.
  • Press the Next button.
  • Start your Android application on the emulator. To build, install and run your application the Android Application, select your project, right click on it, and select Run-As → Android Application.
  • This starts application on the AVD. The started application is a simple Hello, world application.

Android Manifests File​

  • Every application must have an AndroidManifest.xml file.
  • The manifest file presents essential information about your app to the Android system.

The Activity Class​

  • An activity is a window that contains the user interface of the application.
  • It is an application component that provides a screen with which users can interact in order to do something.
  • Creating an activity: 
    package com.example.Activity101;
    import android.app.Activity;
    import android.os.Bundle;
    import com.example.Activity101.R;
    public class MainActivity extends Activity {
        @Override 
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
        }
    }

Activity Life Cycle​

  • Activities transition through states such as onCreate(), onStart(), onResume(), onPause(), onStop(), onRestart(), and onDestroy().

Default and Launcher Activities​

  • The activity which is created by default while making our Android project is known as default activity.
  • The activity via which we launch our application is known as launcher activity.

Activity Stack (Task and Back Stack)​

  • An application usually contains multiple activities.
  • Activities are managed in a stack (back stack).
  • Activities transition between states based on user interactions and system events.

Intents​

  • Intent is an abstract description of an operation to be performed.
  • It can be used to launch activities, broadcast intents, and start services.

Permissions​

  • Permissions restrict access to certain features or data on the device.
  • Permissions are declared in the AndroidManifest.xml file.

Examples of Permissions​

  • ACCOUNT_MANAGER
  • BATTERY_STATS
  • BLUETOOTH
  • CAMERA
  • CALL_PHONE
  • DEVICE_POWER
  • FLASHLIGHT
  • INTERNET
  • READ_CALENDAR
  • READ_CONTACTS
  • READ_SMS
  • REBOOT
  • RECEIVE_MMS
  • RECEIVE_SMS
  • RECORD_AUDIO
  • SEND_SMS
  • SET_ALARM
  • SET_WALLPAPER
  • VIBRATE
  • WRITE_CALENDAR
  • WRITE_CONTACTS
  • WRITE_SMS etc.