Flow basics in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple Flow that emits numbers from 1 to 3.

Android Kotlin

val numbersFlow = flow {
    for (i in 1..[1]) {
        emit(i)
    }
}

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

A0

B5

C10

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as the upper bound results in no emissions.

Using 5 or 10 emits more numbers than required.

The flow emits numbers from 1 to 3, so the range should be 1..3.

2fill in blank

medium

Complete the code to collect and print each value emitted by the Flow.

Android Kotlin

numbersFlow.[1] { value ->
    println(value)
}

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

Amap

Bcollect

ClaunchIn

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using launchIn without a CoroutineScope causes errors.

Using map or filter does not collect values.

To receive and handle emitted values from a Flow, use the collect function.

3fill in blank

hard

Fix the error in the code to emit strings instead of integers.

Android Kotlin

val stringFlow = flow {
    for (i in 1..3) {
        emit([1])
    }
}

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

Ai.toString()

Bi

C"i"

Di + ""

Attempts:

3 left

💡 Hint

Common Mistakes

Emitting i emits integers, not strings.

Using "i" emits the literal letter i, not the number.

To emit strings, convert the integer i to string using toString().

4fill in blank

hard

Fill both blanks to create a Flow that emits only even numbers from 1 to 5.

Android Kotlin

val evenFlow = flow {
    for (num in 1..5) {
        if (num [1] 2 == 0) {
            emit(num[2])
        }
    }
}

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

A%

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using * or + in the if condition causes wrong checks.

Adding operators after emit(num) causes syntax errors.

The modulo operator % checks if a number is even by testing remainder 0. The emit function just emits the number as is, so no operator needed after num.

5fill in blank

hard

Fill all three blanks to create a Flow that emits squares of numbers greater than 2 from 1 to 4.

Android Kotlin

val squaresFlow = flow {
    for (x in 1..4) {
        if (x [1] 2) {
            emit(x [2] x)
        }
    }
}

squaresFlow.collect { value ->
    println(value [3] 0)
}

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

A>

B*

C>=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using >= instead of > changes the condition.

Using == in the print condition prints false instead of true.

We check if x is greater than 2 using >. Then emit the square by multiplying x by x. Finally, print whether each value is greater than 0.

Practice

1. What is the primary purpose of a Flow in Kotlin?

easy

A. To represent a stream of data that can emit multiple values over time

B. To store a single immutable value

C. To create a user interface layout

D. To handle exceptions synchronously

Solution

1. Step 1: Understand what Flow represents

   A Flow is designed to emit multiple values asynchronously over time, like a stream of data.

2. Step 2: Compare options with Flow's purpose

   Only To represent a stream of data that can emit multiple values over time correctly describes Flow as a stream of data emitting multiple values over time.

3. Final Answer:

   To represent a stream of data that can emit multiple values over time -> Option A

4. Quick Check:

   Flow = stream of data [OK]

Hint: Flow emits multiple values over time, not just one [OK]

Common Mistakes:

• Confusing Flow with a single value container like LiveData
• Thinking Flow is for UI layout
• Assuming Flow handles exceptions synchronously

2. Which of the following is the correct way to create a Flow that emits numbers 1 to 3?

easy

A. val flow = flow { emit(1); emit(2); emit(3) }

B. val flow = flowOf(1, 2, 3)

C. All of the above

D. val flow = listOf(1, 2, 3).asFlow()

Solution

1. Step 1: Review Flow creation methods

   Kotlin provides multiple ways to create flows: using flow builder with emit, flowOf, and converting collections with asFlow().

2. Step 2: Check each option

   val flow = flow { emit(1); emit(2); emit(3) } uses flow builder with emit calls, B uses flowOf, and C converts a list to flow. All are valid ways.

3. Final Answer:

   All of the above -> Option C

4. Quick Check:

   Multiple ways to create Flow = D [OK]

Hint: Remember flow, flowOf, and asFlow() all create flows [OK]

Common Mistakes:

• Thinking only flow builder with emit works
• Confusing flowOf with a list
• Not knowing asFlow() converts collections

3. What will be printed by this code?

val flow = flow {
  emit(10)
  emit(20)
}

runBlocking {
  flow.collect { value -> println(value) }
}

medium

A. No output

B. 20 10

C. Only 10

D. 10 20

Solution

1. Step 1: Understand flow emission order

   The flow emits 10 first, then 20 in order.

2. Step 2: Collect prints emitted values in order

   Collect receives values in the same order they are emitted, so prints 10 then 20.

3. Final Answer:

   10 20 -> Option D

4. Quick Check:

   Flow emits in order = 10 20 [OK]

Hint: Flow emits values in order unless otherwise specified [OK]

Common Mistakes:

• Assuming values print in reverse order
• Expecting only first value to print
• Forgetting to run collect inside coroutine

4. Identify the error in this code snippet:

val flow = flow {
  emit(1)
  emit(2)
}

flow.collect { println(it) }

medium

A. Missing coroutine scope to call collect

B. emit() cannot be called inside flow builder

C. collect should be replaced with collectLatest

D. No error, code is correct

Solution

1. Step 1: Check how collect is called

   collect is a suspend function and must be called inside a coroutine or suspend function.

2. Step 2: Analyze code context

   Here, collect is called directly without coroutine scope like runBlocking or launch, causing error.

3. Final Answer:

   Missing coroutine scope to call collect -> Option A

4. Quick Check:

   collect needs coroutine scope [OK]

Hint: Always call collect inside coroutine scope [OK]

Common Mistakes:

• Calling collect outside coroutine
• Thinking emit() is invalid inside flow
• Confusing collect with collectLatest necessity

5. You want to create a Flow that emits numbers 1 to 5 but only collect even numbers. Which code correctly achieves this?

hard

A. val flow = flow {
for (i in 1..5) emit(i)
}

runBlocking {
flow.collect { if (it % 2 == 0) println(it) }
}

B. All of the above

C. val flow = flow {
for (i in 1..5) if (i % 2 == 0) emit(i)
}

runBlocking {
flow.collect { println(it) }
}

D. val flow = flowOf(1, 2, 3, 4, 5)

runBlocking {
flow.filter { it % 2 == 0 }.collect { println(it) }
}

Solution

1. Step 1: Analyze each code snippet

   val flow = flow { for (i in 1..5) emit(i) } runBlocking { flow.collect { if (it % 2 == 0) println(it) } } emits all numbers and filters during collect; C emits only even numbers directly; D uses filter operator before collect.

2. Step 2: Confirm all produce only even numbers on collect

   All options print only even numbers 2 and 4 when collected.

3. Final Answer:

   All of the above -> Option B

4. Quick Check:

   Multiple ways to filter Flow = B [OK]

Hint: Filter before or during collect both work [OK]

Common Mistakes:

• Thinking filter must be before collect only
• Not realizing emit can be conditional
• Forgetting to run collect inside coroutine