Android android:onClick Must Reference an Existing Function

ID

kotlin.android_onclick_exists

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Kotlin

Tags

android, best-practice, reliability

Description

Reports Android layout XML elements that declare android:onClick="methodName" when no Kotlin function named methodName is defined anywhere in the scanned project.

Rationale

At runtime, the framework resolves android:onClick values by reflection against the containing Activity. If the named function does not exist, the first tap that triggers the handler raises IllegalStateException: Could not find method X in a parent or ancestor Context. The bug is invisible at compile time — the XML and Kotlin sources do not share type-level bindings — so the failure only surfaces during manual testing or in the field.

<!-- layout/activity_main.xml -->
<Button
    android:id="@+id/login"
    android:onClick="handleLogin" /> <!-- handleLogin() must exist in the Activity -->
// MainActivity.kt  — missing the expected handler
class MainActivity : Activity() {
    // no handleLogin(view: View) defined => runtime crash on first click
}

Remediation

Either declare the handler function in the Activity or use a runtime binding (findViewById(…​).setOnClickListener { …​ }) which is compile-time checked.

class MainActivity : Activity() {
    fun handleLogin(view: View) {
        // ...
    }
}

References