feat(posts): add 'How to fix Android React Native error "Duplicate class"'

Post: 2025-04-02-how-to-fix-android-react-native-error-duplicate-class.md

Author: remarkablemark

_posts/2025/2025-04-02-how-to-fix-android-react-native-error-duplicate-class.md

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+---
+layout: post
+title: How to fix Android React Native error "Duplicate class"
+date: 2025-04-02 16:47:21
+excerpt: How to fix Android React Native error "Duplicate class".
+categories: expo react native android error
+---
+
+## Problem
+
+If you're getting the error when running [React Native](https://reactnative.dev/) or [Expo](https://expo.dev/) for [Android](https://www.android.com/):
+
+```
+FAILURE: Build failed with an exception.
+
+* What went wrong:
+Execution failed for task ':app:checkDebugDuplicateClasses'.
+> A failure occurred while executing com.android.build.gradle.internal.tasks.CheckDuplicatesRunnable
+   > Duplicate class android.support.v4.app.INotificationSideChannel found in modules core-1.13.1.aar -> core-1.13.1-runtime (androidx.core:core:1.13.1) and support-compat-26.1.0.aar -> support-compat-26.1.0-runtime (com.android.support:support-compat:26.1.0)
+
+     Go to the documentation to learn how to <a href="d.android.com/r/tools/classpath-sync-errors">Fix dependency resolution errors</a>.
+
+* Try:
+> Run with --stacktrace option to get the stack trace.
+> Run with --info or --debug option to get more log output.
+> Run with --scan to get full insights.
+> Get more help at https://help.gradle.org.
+
+BUILD FAILED in 13s
+Error: ./android/gradlew app:assembleDebug -x lint -x test --configure-on-demand --build-cache -PreactNativeDevServerPort=8081 -PreactNativeArchitectures=arm64-v8a exited with non-zero code: 1
+```
+
+The build fails because there are duplicated classes in 2+ dependencies and the compiler doesn't know which one to use during runtime.
+
+This happens when you're importing modules that carry their own required libraries, which leads to transitive dependencies.
+
+## Solution
+
+The solution is to exclude duplicated classes from libraries in `android/app/build.gradle`:
+
+```gradle
+apply plugin: "com.android.application"
+// ...
+
+android {
+    // ...
+    configurations {
+        all {
+            exclude group: "com.android.support"
+            exclude module: "appcompat-v7"
+            exclude module: "support-v4"
+        }
+    }
+}
+```
+
+See Stackoverflow answers [1](https://stackoverflow.com/a/56029604) and [2](https://stackoverflow.com/a/56334710).