Passing data between activities in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of Intent extras in Android?

Intent extras are used to pass small amounts of data between activities in an Android app. They act like a bundle of key-value pairs attached to the Intent.

beginner

How do you add data to an Intent before starting a new activity?

Use the putExtra() method on the Intent object, providing a key and a value. For example: intent.putExtra("username", "Alice")

beginner

How does the receiving activity retrieve data passed via Intent extras?

In the receiving activity, call intent.getStringExtra("key") or the appropriate getExtra method inside onCreate() to get the data sent from the previous activity.

intermediate

What happens if you try to get an extra with a key that was not sent?

The getExtra method returns null (or a default value for primitives). Always check for null to avoid crashes.

intermediate

Can you pass complex objects between activities using Intent extras?

Yes, but the objects must implement Parcelable or Serializable interfaces to be passed via Intent extras.

Which method is used to add data to an Intent before starting a new activity?

A putExtra()

B getExtra()

C startActivity()

D setContentView()

putExtra() adds key-value data to the Intent to pass to the next activity.

How do you retrieve a String extra named "user" in the receiving activity?

A startActivity(intent)

B intent.getStringExtra("user")

C getIntent().putExtra("user")

D intent.getExtra("user")

Use intent.getStringExtra("user") to get the String value passed with key "user".

What must a custom object implement to be passed via Intent extras?

A Runnable

B Activity

C View

D Parcelable or Serializable

Custom objects must implement Parcelable or Serializable to be passed between activities.

If you try to get an extra that was not sent, what will happen?

A Starts a new activity

B App crashes immediately

C Returns null or default value

D Throws a compile error

Getting a missing extra returns null or a default value; it does not crash but you should check for null.

Which Android component is responsible for starting a new screen (activity)?

A Intent

B View

C Service

D BroadcastReceiver

Intent is used to start new activities and can carry data between them.

Explain how to pass a username string from one activity to another in Android using Kotlin.

Think about how you attach data to the Intent and how the next screen reads it.

Describe how you would pass a custom data object between activities and what requirements that object must meet.

Consider Android's rules for passing complex data.

Practice

1. What is the primary method to send data from one activity to another in Android Kotlin?

easy

A. Use an Intent with putExtra() to attach data.

B. Use a global variable to share data.

C. Call the other activity's method directly.

D. Use a database to pass data instantly.

Solution

1. Step 1: Understand Intent usage

   Intent is the standard way to start a new activity and can carry data with putExtra().

2. Step 2: Recognize data passing method

   putExtra() attaches key-value pairs to the Intent for the next activity to retrieve.

3. Final Answer:

   Use an Intent with putExtra() to attach data. -> Option A

4. Quick Check:

   Intent + putExtra() = Data passing [OK]

Hint: Remember: Intent carries data with putExtra() [OK]

Common Mistakes:

• Trying to call methods of another activity directly
• Using global variables which is not recommended
• Assuming database is needed for simple data passing

2. Which of the following is the correct syntax to add a String extra named "username" to an Intent in Kotlin?

easy

A. intent.setExtra("username", username)

B. intent.addExtra("username" to username)

C. intent.putExtra("username", username)

D. intent.putData("username", username)

Solution

1. Step 1: Recall Intent method for extras

   putExtra() is the correct method to add data to an Intent.

2. Step 2: Check syntax correctness

   putExtra() takes a key and a value as parameters, matching intent.putExtra("username", username).

3. Final Answer:

   intent.putExtra("username", username) -> Option C

4. Quick Check:

   putExtra() syntax correct = intent.putExtra("username", username) [OK]

Hint: Use putExtra(key, value) to add data to Intent [OK]

Common Mistakes:

• Using non-existent methods like addExtra or setExtra
• Confusing putExtra with putData
• Missing quotes around the key string

3. Given this code in Activity A:

val intent = Intent(this, ActivityB::class.java)
intent.putExtra("age", 25)
startActivity(intent)

What code correctly retrieves the "age" integer in Activity B?

medium

A. val age = intent.getIntExtra("age", 0)

B. val age = intent.getStringExtra("age")

C. val age = intent.getExtra("age") as Int

D. val age = intent.getInt("age")

Solution

1. Step 1: Identify the data type sent

   The value sent is an integer 25, so we must retrieve it as an Int.

2. Step 2: Use correct retrieval method

   getIntExtra() retrieves an Int extra with a default fallback value.

3. Final Answer:

   val age = intent.getIntExtra("age", 0) -> Option A

4. Quick Check:

   Integer extra retrieval = getIntExtra() [OK]

Hint: Use get<Type>Extra(key, default) matching sent data type [OK]

Common Mistakes:

• Using getStringExtra() for an integer value
• Trying to cast getExtra() without safe methods
• Using non-existent getInt() method

4. What is wrong with this code snippet in Activity B for retrieving a String extra named "email"?

val email = intent.getStringExtra("email")!!

medium

A. getStringExtra() does not exist for Intent.

B. Using !! can cause a crash if "email" extra is missing.

C. The key "email" should be an integer resource ID.

D. Intent extras cannot hold String values.

Solution

1. Step 1: Understand !! operator risk

   Using !! forces a non-null value and crashes if the extra is missing (null).

2. Step 2: Recognize safe retrieval practice

   It's safer to check for null or provide a default instead of forcing !!.

3. Final Answer:

   Using !! can cause a crash if "email" extra is missing. -> Option B

4. Quick Check:

   Unsafe !! usage risks crash [OK]

Hint: Avoid !! on extras; check for null safely [OK]

Common Mistakes:

• Assuming extras always exist without null checks
• Thinking getStringExtra() is invalid
• Confusing keys with resource IDs

5. You want to pass a list of user IDs (List<Int>) from Activity A to Activity B. Which approach correctly sends and retrieves this list?

hard

A. Store the list in a static variable and access it directly in Activity B

B. Use intent.putExtra("userIds", userIds) and retrieve with getIntExtra("userIds", 0)

C. Serialize the list to JSON string and send with putExtra("userIds", jsonString), then parse in Activity B

D. Use intent.putIntegerArrayListExtra("userIds", ArrayList(userIds)) and retrieve with getIntegerArrayListExtra("userIds")

Solution

1. Step 1: Identify correct method for List<Int>

   Intent supports ArrayList<Int> via putIntegerArrayListExtra() and getIntegerArrayListExtra().

2. Step 2: Confirm retrieval matches sending method

   Using these methods ensures type safety and proper data transfer.

3. Final Answer:

   Use intent.putIntegerArrayListExtra("userIds", ArrayList(userIds)) and retrieve with getIntegerArrayListExtra("userIds") -> Option D

4. Quick Check:

   Use put/getIntegerArrayListExtra for List<Int> [OK]

Hint: Use put/getIntegerArrayListExtra for List<Int> [OK]

Common Mistakes:

• Trying to send List<Int> directly with putExtra()
• Using getIntExtra() for a list
• Using static variables which breaks encapsulation