Fix Kotlin compilation error: Return type mismatch in getExportedCustomDirectEventTypeConstants()

[lncitador]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used patch-package to patch react-native-blurhash@2.1.2 for the project I'm working on.

Problem Description

When building the Android app with React Native 0.81.5 and Expo SDK 54, I encountered a Kotlin compilation error in BlurhashViewManager.kt:

Return type mismatch: expected 'MutableMap<String, Any>?', actual 'Map<String, Any>'.

The issue occurs in the getExportedCustomDirectEventTypeConstants() method. The method signature requires a return type of MutableMap<String, Any>?, but MapBuilder.builder().build() returns an immutable Map<String, Any>, which causes a type mismatch.

Solution

The fix is simple: convert the immutable Map to a MutableMap by calling .toMutableMap() on the result of .build().

Environment

• react-native-blurhash: 2.1.2
• React Native: 0.81.5
• Expo SDK: 54.0.20
• Kotlin: 2.1.20
• Android Gradle Plugin: Compatible with Expo SDK 54

Here is the diff that solved my problem (showing only the relevant change):

diff --git a/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt b/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
index 9224e9a..7e0fc81 100644
--- a/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
+++ b/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
@@ -114,6 +114,7 @@ class BlurhashViewManager :
         .put(LoadStartEvent.EVENT_NAME, MapBuilder.of("registrationName", "onLoadStart"))
         .put(LoadEndEvent.EVENT_NAME, MapBuilder.of("registrationName", "onLoadEnd"))
         .build()
+        .toMutableMap()
   }
 
   override fun getName() = REACT_CLASS

This ensures that the return type matches the method signature MutableMap<String, Any>?, resolving the compilation error.

This issue body was partially generated by patch-package.

[maintenance-hans]

Guten Tag, Hans here.

Note

New features, bugfixes, updates and other improvements are all handled mostly by @mrousavy in his free time.
To support @mrousavy, please consider 💖 sponsoring him on GitHub 💖.
Sponsored issues will be prioritized.

[lncitador]

Solution using patch-package

Here's an automated solution using patch-package:

1. Install patch-package

npm install --save-dev patch-package

2. Create the patch file

Create a file at patches/react-native-blurhash+2.1.2.patch with the following content:

Click to expand the full patch file

diff --git a/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt b/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
index 0000000..1111111 100644
--- a/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
+++ b/node_modules/react-native-blurhash/android/src/main/java/com/mrousavy/blurhash/BlurhashViewManager.kt
@@ -109,6 +109,7 @@ class BlurhashViewManager :
   override fun getExportedCustomDirectEventTypeConstants(): MutableMap<String, Any>? {
     return MapBuilder.builder<String, Any>()
         .put(LoadErrorEvent.EVENT_NAME, MapBuilder.of("registrationName", "onLoadError"))
         .put(LoadStartEvent.EVENT_NAME, MapBuilder.of("registrationName", "onLoadStart"))
         .put(LoadEndEvent.EVENT_NAME, MapBuilder.of("registrationName", "onLoadEnd"))
         .build()
+        .toMutableMap()
   }

Note: The most important change is in BlurhashViewManager.kt where .toMutableMap() is added after .build() (the last diff block). The full patch file is available at: https://gist.github.com/lncitador/221577e9b132d5468aa5b37f75b682fa

3. Configure the postinstall script

Add the postinstall script to your package.json:

{
  "scripts": {
    "postinstall": "patch-package"
  }
}

4. Apply the patch

Run:

npx patch-package react-native-blurhash

Or simply run:

npm install

The patch will be automatically applied thanks to the postinstall script.

5. Build your project

npm run android
# or
npx expo run:android

The Kotlin compilation error should be resolved! ??

Important notes:

• ? The patch will be applied automatically every time you run npm install
• ? Make sure to commit the patches/ directory to your repository
• ? If you update react-native-blurhash, you may need to recreate the patch