Activity results in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output when returning a result from an Activity?

Consider an Android app where Activity A starts Activity B for a result. Activity B sets the result as Intent with key "user_name" and value "Alice" before finishing. What will Activity A receive in onActivityResult?

Android Kotlin

val intent = Intent()
intent.putExtra("user_name", "Alice")
setResult(Activity.RESULT_OK, intent)
finish()

A Activity A receives RESULT_OK and intent with "user_name" = "Alice"

B Activity A receives RESULT_CANCELED and no data

C Activity A receives RESULT_OK but intent is null

D Activity A crashes due to missing data

💡 Hint

Remember that setResult passes data back to the calling Activity.

When Activity B calls setResult with RESULT_OK and an Intent containing extras, Activity A receives that Intent in onActivityResult with the same extras.

❓ lifecycle

intermediate

What happens if you call finish() without setResult()?

In an Android app, Activity B is started for result by Activity A. Activity B calls finish() without calling setResult(). What result does Activity A receive?

A Activity A receives null Intent and crashes

B Activity A receives RESULT_OK with no data

C Activity A receives RESULT_OK with default data

D Activity A receives RESULT_CANCELED with no data

💡 Hint

If setResult is not called, what is the default result code?

If setResult is not called, the default result code is RESULT_CANCELED and no data is sent back.

📝 Syntax

advanced

Which code snippet correctly starts an Activity for result using the new Activity Result API?

Android introduced a new Activity Result API replacing startActivityForResult. Which snippet correctly registers and launches an Activity for result?

Android Kotlin

val getContent = registerForActivityResult(ActivityResultContracts.GetContent()) { uri: Uri? ->
    // handle the returned Uri
}

// To launch:
getContent.launch("image/*")

A

val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> if (result.resultCode == Activity.RESULT_OK) { val data = result.data } }
launcher.launch(intent)

B

startActivityForResult(intent, REQUEST_CODE)
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) { }

C val launcher = startActivityForResult(intent, REQUEST_CODE)

D

registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> /* no parameters */ }
launcher.launch(intent)

💡 Hint

Look for the correct use of registerForActivityResult with a lambda receiving a result parameter.

Option A correctly uses registerForActivityResult with StartActivityForResult contract and handles the result in the lambda.

🔧 Debug

advanced

Why does onActivityResult not get called after starting an Activity for result?

An app uses startActivityForResult to launch Activity B from Activity A. But onActivityResult in Activity A is never called after Activity B finishes. What is the most likely cause?

A Activity B calls finish() without setResult()

B Activity B is launched with startActivity instead of startActivityForResult

C Activity A overrides onActivityResult but forgets to call super.onActivityResult

D Activity A uses the new Activity Result API but also overrides onActivityResult

💡 Hint

Check how Activity B is started.

If Activity B is started with startActivity instead of startActivityForResult, onActivityResult will not be called.

🧠 Conceptual

expert

What is the advantage of the new Activity Result API over startActivityForResult?

Android introduced the Activity Result API to replace startActivityForResult and onActivityResult. Which is the main advantage of the new API?

A It allows multiple Activities to run simultaneously in the background

B It automatically saves and restores Activity state without extra code

C It simplifies result handling by using lifecycle-aware callbacks and avoids deprecated methods

D It removes the need to create Intents for starting Activities

💡 Hint

Think about lifecycle and code clarity improvements.

The new Activity Result API uses lifecycle-aware components and callbacks, making result handling cleaner and avoiding deprecated methods.

Practice

1. What is the main purpose of registerForActivityResult in Android Kotlin?

easy

A. To create a new fragment instance

B. To start a new activity without expecting a result

C. To register a broadcast receiver

D. To safely receive data back from another activity

Solution

1. Step 1: Understand the role of registerForActivityResult

   This function is designed to handle results from activities started for a result safely and simply.

2. Step 2: Compare with other options

   Starting an activity without expecting a result or registering broadcast receivers are unrelated to this function.

3. Final Answer:

   To safely receive data back from another activity -> Option D

4. Quick Check:

   Activity result handling = A [OK]

Hint: Remember: registerForActivityResult handles returned data safely [OK]

Common Mistakes:

• Confusing it with starting activities without results
• Thinking it registers broadcast receivers
• Assuming it creates fragments

2. Which of the following is the correct syntax to register an activity result launcher in Kotlin?

easy

A. val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ }

B. val launcher = registerActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ }

C. val launcher = registerForResult(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ }

D. val launcher = registerActivity(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ }

Solution

1. Step 1: Identify the correct function name

   The correct function is registerForActivityResult, not any shortened or altered form.

2. Step 2: Check the contract and lambda syntax

   The contract ActivityResultContracts.StartActivityForResult() and lambda parameter { result -> } are correctly used in val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ }.

3. Final Answer:

   val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> /* handle result */ } -> Option A

4. Quick Check:

   Correct function name and syntax = B [OK]

Hint: Look for exact function name: registerForActivityResult [OK]

Common Mistakes:

• Using incorrect function names like registerActivityResult
• Omitting parentheses in contract instantiation
• Wrong lambda syntax

3. Given the following code snippet, what will be printed if the launched activity returns RESULT_OK with intent data containing key "username" = "Alice"?

val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
    if (result.resultCode == Activity.RESULT_OK) {
        val name = result.data?.getStringExtra("username")
        println(name)
    } else {
        println("No data")
    }
}

medium

A. Crash due to null pointer

B. Alice

C. null

D. No data

Solution

1. Step 1: Check the result code condition

   The code checks if result.resultCode == Activity.RESULT_OK, which is true in this case.

2. Step 2: Extract the "username" from intent data

   The intent data contains key "username" with value "Alice", so name will be "Alice" and printed.

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   Result OK with data returns value = D [OK]

Hint: Check resultCode and safely unwrap intent data [OK]

Common Mistakes:

• Ignoring resultCode and printing 'No data'
• Assuming data is null without checking
• Not using safe call operator on intent data

4. Identify the error in this code snippet for handling activity results:

val launcher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
    val name = result.data!!.getStringExtra("username")
    if (result.resultCode == Activity.RESULT_OK) {
        println(name)
    }
}

medium

A. Unsafe call on result.data before checking resultCode

B. Missing lambda parameter in registerForActivityResult

C. Incorrect contract used for activity result

D. No error, code is correct

Solution

1. Step 1: Analyze the order of operations

   The code force unwraps result.data!! before checking if result.resultCode == Activity.RESULT_OK.

2. Step 2: Understand potential crash

   If the result is not OK or data is null, force unwrapping causes a crash. The check should come before accessing data.

3. Final Answer:

   Unsafe call on result.data before checking resultCode -> Option A

4. Quick Check:

   Check resultCode before accessing data = A [OK]

Hint: Always check resultCode before using intent data [OK]

Common Mistakes:

• Force unwrapping nullable data without checks
• Accessing data before verifying resultCode
• Ignoring null safety in Kotlin

5. You want to start an activity to pick a contact and get the contact's URI back. Which approach correctly uses registerForActivityResult to achieve this?

hard

A. val pickContact = registerForActivityResult(ActivityResultContracts.RequestPermission()) { granted -> if (granted) println("Permission granted") }

B. val pickContact = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> println(result.data?.getData().toString()) }

C. val pickContact = registerForActivityResult(ActivityResultContracts.PickContact()) { uri -> if (uri != null) println(uri.toString()) }

D. val pickContact = registerForActivityResult(ActivityResultContracts.TakePicture()) { success -> if (success) println("Picture taken") }

Solution

1. Step 1: Identify the correct contract for picking a contact

   ActivityResultContracts.PickContact() is designed to pick a contact and return its URI.

2. Step 2: Check the lambda parameter and usage

   The lambda receives a URI nullable parameter, which is safely checked before printing.

3. Step 3: Eliminate other options

   val pickContact = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result -> println(result.data?.getData().toString()) } uses a generic contract but does not check resultCode; A and D are unrelated contracts for permissions and taking pictures.

4. Final Answer:

   val pickContact = registerForActivityResult(ActivityResultContracts.PickContact()) { uri -> if (uri != null) println(uri.toString()) } -> Option C

5. Quick Check:

   Use PickContact contract for contact URI = C [OK]

Hint: Use specific contracts like PickContact for contact picking [OK]

Common Mistakes:

• Using StartActivityForResult without checking resultCode
• Confusing permission or picture contracts with contact picking
• Not handling nullable URI safely