Pagination basics in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the initial page number to 1.

Android Kotlin

var currentPage = [1]

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

A1

B0

Cnull

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting page number at 0 instead of 1.

Using null or negative numbers for page.

The first page number in pagination usually starts at 1 to represent the first set of data.

2fill in blank

medium

Complete the code to increase the page number by 1 when loading the next page.

Android Kotlin

currentPage [1] 1

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

A+=

B/=

C*=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' which decreases the page number.

Using multiplication or division operators.

To move to the next page, you add 1 to the current page number.

3fill in blank

hard

Fix the error in the code to correctly check if the current page is the last page.

Android Kotlin

if (currentPage [1] totalPages) {
    // No more pages to load
}

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

A<

B==

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '>' which check for less or greater, not equality.

Using '!=' which checks for inequality.

To check if the current page is the last page, compare if currentPage equals totalPages.

4fill in blank

hard

Fill both blanks to create a function that returns true if there are more pages to load.

Android Kotlin

fun hasMorePages(currentPage: Int, totalPages: Int): Boolean {
    return currentPage [1] totalPages
}

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

A>

B==

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' which would be true after last page.

Using '==' which only checks equality.

The function should return true if the current page is less than total pages, meaning more pages exist.

5fill in blank

hard

Fill all three blanks to create a map of page numbers to their data lists, filtering only pages with data.

Android Kotlin

val pagesData = mapOf(
    [1] to listOf("Item1", "Item2"),
    [2] to listOf(),
    [3] to listOf("Item3")
).filter { it.value.isNotEmpty() }

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

A1

B2

C3

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-consecutive or invalid page numbers.

Using page numbers not matching the data.

The map keys are page numbers 1, 2, and 3. The filter removes pages with empty lists, so page 2 is excluded.

Practice

1. What is the main purpose of pagination in mobile apps?

easy

A. To split data into smaller pages for faster loading and less memory use

B. To combine all data into one big list

C. To delete old data permanently

D. To change the app's theme colors

Solution

1. Step 1: Understand pagination concept

   Pagination divides large data into smaller parts called pages.

2. Step 2: Identify benefits of pagination

   This helps apps load data faster and use less memory by not loading everything at once.

3. Final Answer:

   To split data into smaller pages for faster loading and less memory use -> Option A

4. Quick Check:

   Pagination = split data for speed and memory [OK]

Hint: Pagination means loading data in small parts, not all at once [OK]

Common Mistakes:

• Thinking pagination deletes data
• Believing pagination merges all data
• Confusing pagination with UI themes

2. Which Kotlin code snippet correctly represents fetching page 2 with page size 10?

easy

A. val page = 2
val size = 10
val start = size - page

B. val page = 2
val size = 10
val start = page * size

C. val page = 2
val size = 10
val start = (page - 1) * size

D. val page = 2
val size = 10
val start = page + size

Solution

1. Step 1: Calculate start index for page 2

   Start index = (page number - 1) * page size, so (2 - 1) * 10 = 10.

2. Step 2: Check code snippets

   val page = 2 val size = 10 val start = (page - 1) * size uses correct formula; others use wrong math.

3. Final Answer:

   val start = (page - 1) * size -> Option C

4. Quick Check:

   Start index formula = (page - 1) * size [OK]

Hint: Start index = (page - 1) times page size [OK]

Common Mistakes:

• Using page * size instead of (page - 1) * size
• Subtracting page from size incorrectly
• Adding page and size instead of multiplying

3. Given this Kotlin code snippet, what will be printed?

val page = 3
val size = 5
val start = (page - 1) * size
println("Loading items from index $start to ${start + size - 1}")

medium

A. Loading items from index 10 to 14

B. Loading items from index 15 to 19

C. Loading items from index 5 to 9

D. Loading items from index 0 to 4

Solution

1. Step 1: Calculate start index

   start = (3 - 1) * 5 = 2 * 5 = 10.

2. Step 2: Calculate end index

   end = start + size - 1 = 10 + 5 - 1 = 14.

3. Final Answer:

   Loading items from index 10 to 14 -> Option A

4. Quick Check:

   Start=10, End=14 [OK]

Hint: End index = start + size - 1 for page ranges [OK]

Common Mistakes:

• Calculating start as page * size
• Forgetting to subtract 1 for end index
• Mixing up start and end indexes

4. What is wrong with this Kotlin pagination code?

val page = 1
val size = 10
val start = page * size
println("Loading items from index $start to ${start + size - 1}")

medium

A. Page size should be multiplied by 2

B. Start index calculation is off by one page

C. Page number should start from 0

D. No error, code is correct

Solution

1. Step 1: Check start index formula

   Correct formula is (page - 1) * size, but code uses page * size.

2. Step 2: Understand impact

   For page 1, start should be 0, but code gives 10, skipping first 10 items.

3. Final Answer:

   Start index calculation is off by one page -> Option B

4. Quick Check:

   Start index must be (page - 1) * size [OK]

Hint: Page 1 start index is zero, so subtract 1 in formula [OK]

Common Mistakes:

• Using page * size instead of (page - 1) * size
• Starting page count at 0 incorrectly
• Assuming no off-by-one errors

5. You want to load pages of data in your app. If the total data size is 47 items and page size is 10, how many pages do you need to load all items?

hard

A. 4

B. 7

C. 6

D. 5

Solution

1. Step 1: Calculate full pages

   47 items divided by 10 per page gives 4 full pages (4 * 10 = 40 items).

2. Step 2: Account for leftover items

   Remaining 7 items need an extra page, so total pages = 4 + 1 = 5.

3. Step 3: Re-check calculation

   Wait, 4 full pages cover 40 items, leftover 7 items need 1 page, total 5 pages.

4. Final Answer:

   5 -> Option D

5. Quick Check:

   Pages = ceil(47/10) = 5 [OK]

Hint: Divide total items by page size and round up [OK]

Common Mistakes:

• Using integer division without rounding up
• Counting only full pages
• Miscounting leftover items