remember and mutableStateOf in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you use mutableStateOf without remember?

Consider this Compose code snippet:

var count by mutableStateOf(0)
Button(onClick = { count++ }) {
  Text("Count: $count")
}

What will happen when you click the button multiple times?

Android Kotlin

var count by mutableStateOf(0)
Button(onClick = { count++ }) {
  Text("Count: $count")
}

A The count will reset to 0 on every recomposition, so UI never shows increment.

B The count will increase but UI will not update to show changes.

C The count will increase and UI updates correctly on each click.

D The app will crash with an exception about state management.

💡 Hint

Think about what happens to variables declared outside remember during recomposition.

Without remember, mutableStateOf is re-initialized on every recomposition, resetting count to 0 each time. So the UI never shows increments.

📝 Syntax

intermediate

Identify the correct syntax to declare a mutable state variable with remember

Which of the following Kotlin Compose code snippets correctly declares a mutable state variable named "text" initialized to an empty string using remember and mutableStateOf?

A val text by mutableStateOf("")

B val text = remember { mutableStateOf("") }

C var text = mutableStateOf("") remember

D var text by remember { mutableStateOf("") }

💡 Hint

Remember that remember is a function that takes a lambda returning mutableStateOf.

Option D uses 'by' delegation with remember { mutableStateOf("") }, which is the correct pattern to declare a mutable state variable in Compose.

❓ lifecycle

advanced

How does remember behave across recompositions?

In Jetpack Compose, what is the behavior of a variable declared with remember when the composable function recomposes?

A The variable is reset only when the app process is killed.

B The variable is re-initialized every time the composable recomposes.

C The variable keeps its value across recompositions until the composable leaves the composition.

D The variable is shared globally across all composables.

💡 Hint

Think about how remember helps keep state during recomposition but not beyond the composable lifecycle.

remember stores the value in the composition and keeps it across recompositions, but resets when the composable leaves the composition.

🔧 Debug

advanced

Why does this Compose UI not update when state changes?

Given this code:

@Composable
fun Counter() {
  var count = remember { 0 }
  Button(onClick = { count++ }) {
    Text("Count: $count")
  }
}

Why does the UI not update when the button is clicked?

Android Kotlin

@Composable
fun Counter() {
  var count = remember { 0 }
  Button(onClick = { count++ }) {
    Text("Count: $count")
  }
}

A Because count is not a mutable state, so Compose does not track changes to it.

B Because remember cannot be used with integers.

C Because count should be declared as val, not var.

D Because Button onClick cannot modify variables.

💡 Hint

Check if the variable is wrapped in mutableStateOf to notify Compose of changes.

The variable count is just an integer remembered, but not a mutable state. Compose does not recompose when it changes.

🧠 Conceptual

expert

What is the main difference between remember and mutableStateOf in Jetpack Compose?

Choose the best explanation of the difference between remember and mutableStateOf:

A remember triggers recomposition on value change; mutableStateOf stores a value across recompositions.

B remember stores a value across recompositions; mutableStateOf creates a state holder that triggers recomposition on value change.

C Both remember and mutableStateOf do the same thing and can be used interchangeably.

D mutableStateOf is used only for immutable values; remember is for mutable values.

💡 Hint

Think about what each function does in terms of state storage and recomposition triggers.

remember keeps a value alive during recompositions; mutableStateOf creates a state object that notifies Compose to recompose when changed.