Activity lifecycle methods (onCreate, onStart, onResume, onPause, onStop, onDestroy) in Android Kotlin - Mini App: Build & Ship

Build: Lifecycle Demo Screen

This screen shows messages on the screen each time an activity lifecycle method is called. It helps you see when onCreate, onStart, onResume, onPause, onStop, and onDestroy happen.

Target UI

-------------------------
| Lifecycle Demo Screen  |
|-----------------------|
| Messages:             |
| - onCreate called     |
| - onStart called      |
| - onResume called     |
|                       |
| (Messages update live) |
-------------------------

Display a TextView that updates with the name of the lifecycle method called

Override all six lifecycle methods: onCreate, onStart, onResume, onPause, onStop, onDestroy

Each method appends its name to the TextView on a new line

Use setContentView with a simple layout containing only the TextView

Ensure the TextView scrolls if messages get too long

Starter Code

Android Kotlin

package com.example.lifecycledemo

import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var lifecycleTextView: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // TODO: Set content view and initialize lifecycleTextView
    }

    // TODO: Override other lifecycle methods here
}

Task 1

Task 2

Task 3

Solution

Android Kotlin

package com.example.lifecycledemo

import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var lifecycleTextView: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        lifecycleTextView = findViewById(R.id.lifecycleTextView)
        appendMessage("onCreate called")
    }

    override fun onStart() {
        super.onStart()
        appendMessage("onStart called")
    }

    override fun onResume() {
        super.onResume()
        appendMessage("onResume called")
    }

    override fun onPause() {
        super.onPause()
        appendMessage("onPause called")
    }

    override fun onStop() {
        super.onStop()
        appendMessage("onStop called")
    }

    override fun onDestroy() {
        super.onDestroy()
        appendMessage("onDestroy called")
    }

    private fun appendMessage(message: String) {
        lifecycleTextView.append("$message\n")
    }
}

We override all six lifecycle methods to track when each is called. In each method, we add a line of text to the TextView to show the event. The TextView is initialized in onCreate after setting the content view. This way, as the activity moves through its lifecycle, the user sees messages updating live on the screen.

The layout file activity_main.xml should contain a ScrollView with a TextView inside to allow scrolling when messages overflow.

Final Result

Completed Screen

-------------------------
| Lifecycle Demo Screen  |
|-----------------------|
| Messages:             |
| onCreate called       |
| onStart called        |
| onResume called       |
|                       |
| (Scroll if needed)    |
-------------------------

When the app starts, 'onCreate called', 'onStart called', and 'onResume called' messages appear in order.

When the app goes to background, 'onPause called' and 'onStop called' appear.

When the app is closed, 'onDestroy called' appears.

Messages keep appending so user can see lifecycle flow.

Stretch Goal

Add a button that clears all lifecycle messages from the TextView.

💡 Hint

Add a Button below the TextView in the layout. Set an onClickListener that sets lifecycleTextView.text = "".

Practice

1. Which lifecycle method is called first when an Android activity is launched?
onCreate(), onStart(), onResume(), or onPause()?

easy

A. onStart()

B. onResume()

C. onCreate()

D. onPause()

Solution

1. Step 1: Understand activity launch sequence

   When an activity starts, onCreate() is the first method called to set up the UI and initialize components.

2. Step 2: Confirm order of lifecycle methods

   After onCreate(), onStart() and onResume() follow, but they are not first.

3. Final Answer:

   onCreate() -> Option C

4. Quick Check:

   First lifecycle method = onCreate() [OK]

Hint: Remember: onCreate() is always first when activity starts [OK]

Common Mistakes:

• Confusing onStart() as the first method
• Thinking onResume() is called before onCreate()
• Assuming onPause() is called on launch

2. Which of the following is the correct Kotlin syntax to override the onPause() method in an Android activity?

easy

A. override fun onPause() {
pause.super()
}

B. fun onPause() {
super.onPause()
}

C. override onPause() {
super.onPause()
}

D. override fun onPause() {
super.onPause()
}

Solution

1. Step 1: Check Kotlin override syntax

   In Kotlin, to override a method, use override fun methodName() and call super.methodName() inside.

2. Step 2: Validate each option

   override fun onPause() { super.onPause() } correctly uses override fun onPause() and calls super.onPause(). Others miss override keyword, have wrong syntax, or wrong super call.

3. Final Answer:

   override fun onPause() { super.onPause() } -> Option D

4. Quick Check:

   Correct override syntax = override fun onPause() { super.onPause() } [OK]

Hint: Always use 'override fun method()' and call 'super.method()' inside [OK]

Common Mistakes:

• Omitting the override keyword
• Calling super incorrectly
• Wrong function declaration syntax

3. Consider this Kotlin code snippet inside an activity:

override fun onPause() {
    super.onPause()
    println("Paused")
}
override fun onStop() {
    super.onStop()
    println("Stopped")
}

What will be printed if the user presses the home button while the activity is visible?

medium

A. Stopped
Paused

B. Paused
Stopped

C. Paused

D. Stopped

Solution

1. Step 1: Understand lifecycle on home press

   Pressing home triggers onPause() first, then onStop() as activity goes to background.

2. Step 2: Check print order

   Since onPause() runs before onStop(), "Paused" prints first, then "Stopped".

3. Final Answer:

   Paused Stopped -> Option B

4. Quick Check:

   onPause() then onStop() prints = Paused, Stopped [OK]

Hint: onPause() always runs before onStop() when leaving activity [OK]

Common Mistakes:

• Assuming onStop() runs before onPause()
• Thinking only one method runs on home press
• Confusing print order

4. This code snippet is intended to save data when the activity is paused:

override fun onPause() {
    saveData()
}

What is the main problem with this code?

medium

A. Missing call to super.onPause()

B. saveData() should be called in onStop() instead

C. onPause() cannot be overridden

D. saveData() must be asynchronous

Solution

1. Step 1: Check lifecycle method override rules

   When overriding lifecycle methods, always call super.method() to keep system stable.

2. Step 2: Identify missing super call

   The code lacks super.onPause(), which can cause unexpected behavior.

3. Final Answer:

   Missing call to super.onPause() -> Option A

4. Quick Check:

   Always call super in lifecycle overrides [OK]

Hint: Never forget super.onPause() when overriding onPause() [OK]

Common Mistakes:

• Forgetting to call super method
• Thinking onPause() can't be overridden
• Assuming saveData() timing is wrong

5. You want to release a camera resource when the activity is no longer visible to save battery. Which lifecycle method is the best place to release the camera?
A) onDestroy()
B) onStop()
C) onPause()
D) onResume()

hard

A. onPause()

B. onStop()

C. onDestroy()

D. onResume()

Solution

1. Step 1: Understand visibility and resource management

   When activity is partially or fully hidden, onPause() is called first, signaling to release resources like camera to save battery.

2. Step 2: Compare lifecycle methods for releasing resources

   onStop() is later, but releasing in onPause() ensures resources are freed as soon as activity is not in foreground. onDestroy() may never be called if system kills process. onResume() is for acquiring resources.

3. Final Answer:

   onPause() -> Option A

4. Quick Check:

   Release resources in onPause() to save battery [OK]

Hint: Release heavy resources in onPause(), reacquire in onResume() [OK]

Common Mistakes:

• Waiting until onStop() or onDestroy() to release resources
• Releasing resources in onResume() by mistake
• Not releasing resources early enough