Android Wdigets, Activities and Notifications - Overview

Snackbar

• Provides lightweight feedback about an operation.
• Displays a brief message at the bottom of the screen.
• Automatically disappears after a timeout.
• Similar to a Toast but can include an action button.
• Implemented using the Snackbar class.

Activity

• Main activity is configured in AndroidManifest.xml.
• Each activity must be declared in the manifest file.
• Activities are managed as an activity stack:
  • When an activity starts another, it is pushed on top of the stack.
  • Pressing the Back button pops the current activity from the stack.

Activity Lifecycle

1. Non-existent → Stopped → Paused → Running
2. Developers manage state transitions using lifecycle callbacks:
   • onCreate() → onStart() → onResume()
   • onPause() → onStop() → onDestroy()

Lifecycle Details

• onPause()

  • Activity is partially visible but not in focus.
  • UI updates may still continue.
  • Multi-resume is supported on select devices.

• onStop()

  • Activity is no longer visible.

• onRestart()

  • Always followed by onStart().
  • Called when an activity comes back to the foreground after being stopped but not destroyed.
  • Example: User presses the Home button and later reopens the app.
  • Used to refresh resources or UI elements.

• onResume()

  • Called every time the app comes to the foreground.
  • Example: User switches to another app and then returns.
  • Used to:
    • Resume animations.
    • Refresh dynamic UI.
    • Start listening to sensors.

Android Intent

• Used to move from one activity to another or start another app.
• Two types:
  • Explicit Intent – Targets a specific activity.
  • Implicit Intent – Requests an action from any app that can handle it.

Intent Components

• Action

  • Determines the structure of the intent.
  • Can be a predefined constant (provided by Android) or a custom action string (declared in AndroidManifest.xml).
  • Example actions: Open Camera, Make a Call, Start Voice Command.

• Data

  • Specifies the data to operate on, typically a URI (e.g., file, contact).
  • Works with implicit intents.

• Category (Optional)

  • Adds context about how the intent should be handled (e.g., "Map", "Calendar").
  • Helps Android determine which activities/components can respond.
  • Can modify intent behavior (e.g., open in a specific mode).

• Extra

  • Key-value pairs used to pass additional data.
  • Works with both implicit and explicit intents.
  • Can store primitive types and is delivered to the target activity.

Alert Dialog

• A popup window that includes:
  • Title
  • Message
  • List of selectable items (can use custom views like checkboxes)
  • Action buttons (typically 3: Positive, Negative, Neutral)

Android Notifications

• Managed by Android’s Notification Management Service.
• Components of a notification:
  • Small Icon – Set by the developer.
  • App Name – Automatically assigned.
  • Large Icon – Set by the developer.
  • Timestamp – Automatic (can be overridden by the developer).
  • Title & Text – Set by the developer.

Notification Features by Android Version

• Android 7.0 – Supports direct reply from notifications (RemoteInput).
• Android 10 – Introduced AI-generated action buttons (e.g., Yes, No, Thanks, or opening maps for an address) with MessagingStyle notifications.

Notification Channel (Introduced in Android 8.0):

• Every notification must be assigned to a channel.
• Users can control settings for each channel, including:
  • Enable/Disable notifications.
  • Set importance level.
  • Customize sound and visualization.
• Example Use Case: Instant messaging apps – each chat can have a separate notification channel.
• Requires a channel ID.