Derived state in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a derived state that holds the length of the text.

Android Kotlin

val text = remember { mutableStateOf("") }
val textLength = remember [1] {
    text.value.length
}

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

AmutableStateOf

BderivedStateOf

CrememberUpdatedState

DstateOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableStateOf instead of derivedStateOf causes the length not to update automatically.

Forgetting to use remember causes recomposition issues.

The derivedStateOf function creates a state that automatically updates when its dependencies change. Here, it tracks text.value.length.

2fill in blank

medium

Complete the code to create a derived state that returns true if the text length is greater than 5.

Android Kotlin

val text = remember { mutableStateOf("") }
val isLongText = remember [1] {
    text.value.length > 5
}

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

AderivedStateOf

BmutableStateOf

CrememberUpdatedState

DstateOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableStateOf will not update automatically when text.value changes.

Using rememberUpdatedState is not suitable for derived state.

derivedStateOf is used to create a state that depends on other states and updates automatically. Here, it checks if the text length is greater than 5.

3fill in blank

hard

Fix the error in the code by completing the blank to create a derived state that returns the uppercase version of the text.

Android Kotlin

val text = remember { mutableStateOf("") }
val upperText = remember [1] {
    text.value.uppercase()
}

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

AderivedStateOf

BmutableStateOf

CrememberUpdatedState

DstateOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableStateOf causes the derived state not to update automatically.

Using rememberUpdatedState is not appropriate here.

derivedStateOf is the correct function to create a derived state that updates automatically when text.value changes.

4fill in blank

hard

Fill both blanks to create a derived state that returns true if the text contains the letter 'a' and its length is more than 3.

Android Kotlin

val text = remember { mutableStateOf("") }
val condition = remember [1] {
    text.value.contains('a') && text.value.length [2] 3
}

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

AderivedStateOf

B>

C<

DmutableStateOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableStateOf instead of derivedStateOf.

Using the less than operator instead of greater than.

derivedStateOf creates the derived state. The condition checks if the text contains 'a' and if its length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a derived state that returns a map of words to their lengths, but only for words longer than 4 characters.

Android Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val wordLengths = remember [1] {
    words.filter { it.length [2] 4 }
        .associateWith { it.length [3] }
}

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

AderivedStateOf

B>

Ctrue

DmutableStateOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableStateOf instead of derivedStateOf.

Using less than operator instead of greater than.

Leaving the third blank empty or incorrect.

derivedStateOf creates the derived state. The filter uses the greater than operator to select words longer than 4. The associateWith maps each word to its length, so the lambda returns it.length which is a value, so true is used as a placeholder to complete syntax.