kotlin-diagnostics

Common KotlinSense Diagnostics and Fixes

Unresolved reference

error: unresolved reference: 'FooClass'

Fixes:

• Add the missing import: import com.example.FooClass
• Check for a typo in the class/function name
• Ensure the dependency is in build.gradle.kts (implementation(...))
• Run ./gradlew build if the class is generated (Room, Hilt, etc.)

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Type mismatch

error: type mismatch: inferred type is String but Int was expected

Fixes:

• Add explicit conversion: str.toInt(), num.toString(), num.toLong()
• Use when for sealed class branches to satisfy exhaustiveness
• Check if you're passing the wrong variable to a function

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Null safety violation

error: only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver

Fixes (prefer in this order):

// 1. Safe call — returns null if receiver is null
nullableObj?.method()

// 2. Elvis operator — provide a default
nullableObj?.property ?: defaultValue

// 3. Let block — operate only when non-null
nullableObj?.let { obj ->
    obj.method()
}

// 4. Non-null assertion — only if you're certain it can't be null
nullableObj!!.method()  // crashes with NullPointerException if null

---

Val cannot be reassigned

error: val cannot be reassigned

Fix: Change val to var if reassignment is needed. Prefer val (immutable) by default.

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Override modifier required

error: 'foo' hides member of supertype and needs 'override' modifier

Fix: Add the override keyword:

override fun foo() { ... }
override val bar: String = "value"

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Suspend function called from non-suspend context

error: suspend function 'collect' should be called only from a coroutine or another suspend function

Fix: Call from a coroutine scope:

// In ViewModel
viewModelScope.launch {
    repository.flow.collect { value -> ... }
}

// In Fragment/Activity
viewLifecycleOwner.lifecycleScope.launch {
    viewModel.uiState.collect { state -> render(state) }
}

---

Missing return statement

error: a 'return' expression required in a function with a block body

Fixes:

// Option 1: add explicit return
fun foo(): String {
    return "value"
}

// Option 2: use expression body (preferred for simple functions)
fun foo(): String = "value"

---

GlobalScope usage discouraged

warning: GlobalScope usage is strongly discouraged

Fix: Replace with structured concurrency:

// In ViewModel
viewModelScope.launch { ... }

// In Fragment/Activity
lifecycleScope.launch { ... }

// In a suspend function — use coroutineScope { } for fan-out
coroutineScope {
    launch { ... }
    launch { ... }
}

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Android-specific: View? type mismatch

error: type mismatch: inferred type is View? but View was expected

Fix: Migrate to View Binding or Jetpack Compose. If using XML temporarily:

val button = findViewById<Button>(R.id.myButton) ?: return

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Compose: state read inside non-restartable composable

Fix: Hoist state reads into restartable composables, or use remember:

val count by remember { mutableStateOf(0) }