ConcurrentModificationException

Android

TL;DR

ConcurrentModificationException indicates a concurrency failure on Android that interrupts the current user flow.

Symptoms

ConcurrentModificationException appears in logcat
The app crashes or the action fails

Common Causes

Shared state is mutated without coordination
Object is used after lifecycle termination

How to Verify

Reproduce with deterministic input and capture full logsInspect the first throw site and recent changes around it

Quick Fixes

Add guard checks and a safe fallback path
Disable or rollback the risky code path behind a flag

Proper Fixes

Enforce contracts with types, runtime checks, and tests
Refactor ownership and lifecycle boundaries to remove the failure mode

Example Stack Trace

ConcurrentModificationException at com.example.app.MainActivity.onCreate(MainActivity.kt:42)

Related Errors

NSInvalidArgumentException TypeError Cannot Read Properties Of Undefined NetworkError Failed To Fetch