Bug-Squash Interview - GrindLoop: Android & iOS Interview Prep

Why Gson Returns Null Fields Only in Your Release Build

September 28, 2026 by Arsam

Code editor on a dark monitor showing JSON parsing code, illustrating Gson null fields in an Android release build

A Kotlin data class parsed by Gson works in debug and comes back null in release. Here’s the two-bug reason (R8 plus Gson skipping your constructor), the fix, and the interview answer.

Why Fast Scrolling Duplicates Items in Your Paginated List

September 27, 2026 by Arsam

Close-up of code on a laptop screen, illustrating an Android pagination race condition bug

An Android pagination race condition duplicates list items when two scroll-triggered page loads overlap. Here’s the two-bug reason, the fix, and the interview answer.

Why Your Predictive Back Animation Gets Stuck When the Gesture Is Canceled

September 27, 2026September 25, 2026 by Arsam

Hand holding an Android phone with a blank screen, illustrating a predictive back gesture animation in Jetpack Compose

The predictive back gesture is no longer optional. For apps targeting Android 16 (API level 36), predictive back system animations are enabled by default. Since August 31, 2026, Google Play requires new apps and app updates to target API level 36. So any app still shipping updates is affected. If your app has a custom … Read more

Why Your Kotlin Data Class’s equals() Ignores the Parent Class

September 27, 2026September 24, 2026 by Arsam

Close-up of colorful source code on a computer monitor

The Kotlin data class equals check ignores a parent class’s properties, by design. Why, the hashCode trap in the obvious fix, a correct override and the interview answer.

Why viewModelScope.async Swallows a Failed API Call

September 27, 2026September 22, 2026 by Arsam

Network server rack with blinking status lights and ethernet cables, representing an async API call over the network

A viewModelScope async call that nobody awaits hides its failure completely. Why a root async stores the exception, why the same code inside launch crashes instead, a runnable repro and the fix.

Why EncryptedSharedPreferences Throws KeyPermanentlyInvalidatedException After a New Fingerprint

September 27, 2026September 16, 2026 by Arsam

Code on a monitor at an angle, illustrating a KeyPermanentlyInvalidatedException bug in Android code

A KeyPermanentlyInvalidatedException after a new fingerprint is documented Keystore behavior. Why a plain catch still locks users out, the recovery that deletes the key and data, and the interview answer.

The Null Check That Didn’t Save You

September 27, 2026September 11, 2026 by Arsam

Extreme close-up of code on a screen, illustrating a Compose null check crash

A Compose null check crash happens when a null check and a !! read mutable state twice. Why Kotlin refuses to smart-cast delegated state, the one-read fix and the interview answer.

Why Your Combined StateFlow Shows Stale Data: SharingStarted.Lazily vs Eagerly

September 27, 2026September 5, 2026 by Arsam

Colorful source code on a monitor, illustrating a StateFlow stale data bug in Kotlin

A combined StateFlow returns stale data when stateIn uses SharingStarted.Lazily and a hardcoded Main scope. The two causes, the fix, how to choose a sharing strategy and the interview answer.