Android Basics II — Lifecycle, Configuration Changes, Intents

Key concepts

• onCreate → onStart → onResume → onPause → onStop → onDestroy
• Configuration changes destroy & recreate activities
• onSaveInstanceState / ViewModel
• Explicit vs implicit Intent
• Passing data via Intent extras

Lectures in this day

1. 01

   Activity and Activity Lifecycle

   An Activity is one screen. Android calls special methods on it as it appears and disappears: onCreate (built), onStart (about to show), onResume (visible), onPause (about to hide), onStop (hidden), onDestroy (gone). Set things up in onCreate, and clean up (release camera, save data) in onPause/onStop.

   Real life · A stage play. Actor enters (onCreate), spotlight on (onResume), spotlight dims (onPause), curtain drops (onStop), actor leaves (onDestroy).

   Practice · 3 quick questions

   1. Q1.An Activity is…

      A.A single screen with its own lifecycleB.A databaseC.A layout file

   2. Q2.Which is a lifecycle method?

      A.onCreateB.onDrawC.onCompile

   3. Q3.onCreate is called…

      A.Every time the screen is visibleB.Once when the Activity is first createdC.Never

   Check answersPick one answer per question.
2. 02

   Activity Lifecycle Example

   The easiest way to learn the lifecycle is to see it happen. Add `Log.d(TAG, "onXxx")` in each method, then open Logcat in Android Studio and rotate, press Home, and re-open the app. You'll see the exact order.

   Real life · Putting a small camera above every door in your house to see who comes and goes — you learn the flow by watching.
   kotlin

   Copy

   class MainActivity : AppCompatActivity() {
       private val TAG = "LIFE"
       override fun onCreate(s: Bundle?) { super.onCreate(s); Log.d(TAG, "onCreate") }
       override fun onStart()            { super.onStart();   Log.d(TAG, "onStart") }
       override fun onResume()           { super.onResume();  Log.d(TAG, "onResume") }
       override fun onPause()            { super.onPause();   Log.d(TAG, "onPause") }
       override fun onStop()             { super.onStop();    Log.d(TAG, "onStop") }
       override fun onDestroy()          { super.onDestroy(); Log.d(TAG, "onDestroy") }
   }

   Practice · 3 quick questions

   1. Q1.When you rotate the phone, by default the Activity…

      A.Is destroyed and recreatedB.Stays untouchedC.Crashes

   2. Q2.Which pair is called when leaving to another app?

      A.onPause → onStopB.onCreate → onStartC.onDestroy → onCreate

   3. Q3.Coming back to the app calls…

      A.onStart → onResumeB.onCreate again alwaysC.onDestroy

   Check answersPick one answer per question.
3. 03

   How to Survive Configuration Change

   When you rotate the phone, Android destroys the screen and builds it again — so unsaved data is lost. Save short-lived stuff (a half-typed message) in `onSaveInstanceState` as a Bundle, and read it back in `onCreate`.

   Real life · Leaving your desk for lunch: if you don't leave a sticky note where you stopped, you'll waste 10 minutes finding your place again.
   kotlin

   Copy

   0
   override fun onSaveInstanceState(out: Bundle) {
       super.onSaveInstanceState(out)
       out.putString("draft", editText.text.toString())
   }
   
   1
   override fun onCreate(s: Bundle?) {
       super.onCreate(s)
       setContentView(R.layout.activity_main)
       s?.getString("draft")?.let { editText.setText(it) }
   }

   Practice · 3 quick questions

   1. Q1.One common way to survive rotation is…

      A.ViewModelB.Restart the phoneC.Delete data

   2. Q2.Another simple way is…

      A.Save state in onSaveInstanceStateB.Use a global variableC.Ignore it

   3. Q3.Rotation is a…

      A.Configuration changeB.Network eventC.Sensor error

   Check answersPick one answer per question.
4. 04

   Introducing Intent

   An Intent is a message that says 'please do this'. Explicit intent = 'open THIS screen' (you name the class). Implicit intent = 'anyone able to open a link, please handle this' — the OS finds a matching app.

   Real life · Explicit = calling one specific friend. Implicit = shouting 'anyone driving to the market?' and letting the first taker respond.
   kotlin

   Copy

   0
   startActivity(
       Intent(this, DetailActivity::class.java).putExtra("id", 42)
   )
   
   1
   startActivity(
       Intent(Intent.ACTION_VIEW, Uri.parse("https:2
   )

   Practice · 3 quick questions

   1. Q1.An Intent is used to…

      A.Ask Android to do something (start Activity, share, etc.)B.Draw pixelsC.Compile code

   2. Q2.Which starts another Activity?

      A.startActivity(intent)B.openScreen()C.goTo()

   3. Q3.An implicit Intent…

      A.Names no exact component; the system picks an appB.Always targets your appC.Is invalid

   Check answersPick one answer per question.
5. 05

   View / ViewGroup and Resource Recap

   A View is one visible thing (Button, TextView, ImageView). A ViewGroup is a box that holds other views (LinearLayout, ConstraintLayout). Text, colors, and sizes go in the `res/` folder so you can change them without touching Kotlin code.

   Real life · Views are the actors. ViewGroups are the stage. `res/` is the props warehouse.

   Practice · 3 quick questions

   1. Q1.A ViewGroup is…

      A.A view that holds other viewsB.A single buttonC.A database

   2. Q2.Images in res/drawable are used as…

      A.Drawable resourcesB.Executable codeC.Databases

   3. Q3.Strings should live in…

      A.res/values/strings.xmlB.Kotlin code hardcodedC.A .txt file

   Check answersPick one answer per question.
6. 06

   Android Components Overview

   Android apps are made of 4 main building blocks. Activity = a screen. Service = code that runs in the background (like music playback). BroadcastReceiver = a small listener that wakes up on system events (like 'battery low'). ContentProvider = a way to share data with other apps.

   Real life · A restaurant: dining area (Activity), kitchen (Service), fire alarm (BroadcastReceiver), the recipe book shared with the head office (ContentProvider).

   Practice · 3 quick questions

   1. Q1.Which is NOT one of the 4 core components?

      A.ActivityB.ServiceC.Button

   2. Q2.Services run…

      A.Long tasks without UIB.The keyboardC.Layouts

   3. Q3.BroadcastReceivers react to…

      A.System or app-wide eventsB.Only networkC.Only UI clicks

   Check answersPick one answer per question.
7. 07

   Module 3 Summary

   You can now build a real screen: draw it in XML, wire it in Kotlin, react to lifecycle events, save state on rotation, and move between screens with intents.

   Real life · You've gone from placing bricks to putting up a whole room with a door — next module is decorating and wiring it neatly.

   Practice · 3 quick questions

   1. Q1.Module 3 was mostly about…

      A.First real Android UI & lifecycleB.FirebaseC.Kotlin lambdas

   2. Q2.You should now be able to…

      A.Build a small multi-screen app with IntentsB.Ship to Play Store instantlyC.Train ML models

   3. Q3.Which is NOT in Module 3?

      A.ConstraintLayoutB.Activity lifecycleC.Firestore

   Check answersPick one answer per question.

Real-life analogies

Code examples

class MainActivity : AppCompatActivity() {
    private val tag = "LIFE"
    override fun onCreate(s: Bundle?) { super.onCreate(s); Log.d(tag,"onCreate") }
    override fun onStart()   { super.onStart();   Log.d(tag,"onStart") }
    override fun onResume()  { super.onResume();  Log.d(tag,"onResume") }
    override fun onPause()   { super.onPause();   Log.d(tag,"onPause") }
    override fun onStop()    { super.onStop();    Log.d(tag,"onStop") }
    override fun onDestroy() { super.onDestroy(); Log.d(tag,"onDestroy") }
}

0
val intent = Intent(this, DetailActivity::class.java).apply {
    putExtra("USER_NAME", "Rakib")
    putExtra("USER_AGE", 24)
}
startActivity(intent)

1
val name = intent.getStringExtra("USER_NAME")
val age  = intent.getIntExtra("USER_AGE", 0)

Hands-on checklist

• Add Log.d in all 6 lifecycle callbacks
• Rotate the device and read logcat — trace the callback order
• Save state in onSaveInstanceState and restore it
• Build a 2nd Activity and pass 2 values via Intent extras

Milestone

Common pitfalls

• Storing large data in Bundle — it's for small primitives, not lists of objects.
• Forgetting to register the second Activity in AndroidManifest.xml.