Activity results in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start an activity for result using the new Activity Result API.

Android Kotlin

val getContent = registerForActivityResult([1]) { uri ->
    // Handle the returned Uri
}

Drag options to blanks, or click blank then click option'

AActivityResultContracts.StartActivityForResult()

BActivityResultContracts.GetContent()

CActivityResultContracts.TakePicture()

DActivityResultContracts.RequestPermission()

Attempts:

3 left

💡 Hint

Common Mistakes

Using StartActivityForResult() which returns an ActivityResult, not a Uri.

Using RequestPermission() which is for permissions, not content.

The GetContent() contract lets you pick content and get a Uri result.

2fill in blank

medium

Complete the code to launch the activity to pick an image.

Android Kotlin

getContent.launch([1])

Drag options to blanks, or click blank then click option'

A"application/pdf"

B"text/plain"

C"video/*"

D"image/*"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text/plain' which is for text files.

Using 'video/*' which is for videos.

To pick an image, the MIME type should be "image/*".

3fill in blank

hard

Fix the error in the callback parameter type for the activity result launcher.

Android Kotlin

val getContent = registerForActivityResult(ActivityResultContracts.GetContent()) { [1] ->
    // Use the Uri
}

Drag options to blanks, or click blank then click option'

Auri

Bintent

Cresult

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'intent' or 'data' which are used in the old API.

Using 'result' which is ambiguous.

The callback receives a Uri? named here as uri.

4fill in blank

hard

Fill both blanks to correctly handle the result in the old onActivityResult method.

Android Kotlin

override fun onActivityResult(requestCode: Int, resultCode: Int, [1]: Intent?) {
    super.onActivityResult(requestCode, resultCode, [2])
    if (requestCode == PICK_IMAGE && resultCode == RESULT_OK) {
        val uri = data?.data
        // Use the uri
    }
}

Drag options to blanks, or click blank then click option'

Adata

Bintent

Cresult

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in parameter and super call.

Using 'intent' or 'result' which are not consistent here.

The parameter and the super call both use data as the Intent variable.

5fill in blank

hard

Fill all three blanks to create a map of request codes to their string descriptions.

Android Kotlin

val requestDescriptions = mapOf(
    PICK_IMAGE to [1],
    PICK_VIDEO to [2],
    PICK_AUDIO to [3]
)

Drag options to blanks, or click blank then click option'

A"Pick Image"

B"Pick Video"

C"Pick Audio"

D"Pick Document"

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up descriptions or using unrelated strings.

Using 'Pick Document' which is not in the request codes.

This map links each request code to a descriptive string for clarity.

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