fix(android): keep a strong reference to the fallback font picker

android/src/main/java/com/margelo/nitro/rive/HybridRiveFontConfig.kt

@@ -22,6 +22,11 @@ class HybridRiveFontConfig : HybridRiveFontConfigSpec() {
     private val fontsByWeight: MutableMap<Int, List<HybridFallbackFontSpec>> =
       java.util.Collections.synchronizedMap(mutableMapOf())
 
+    // rive-android holds FontFallbackStrategy.stylePicker only in a WeakReference (#369),
+    // so both fields must be written together under pickerLock.
+    private val pickerLock = Any()
+    private var strongStylePicker: FontFallbackStrategy? = null
+
     private fun resetFontCache() {
       try {
         FontFallbackStrategy.cppResetFontCache()
@@ -100,7 +105,7 @@ class HybridRiveFontConfig : HybridRiveFontConfigSpec() {
 
   override fun applyFallbackFonts(): Promise<Unit> {
     return Promise.async {
-      FontFallbackStrategy.stylePicker = object : FontFallbackStrategy {
+      val picker = object : FontFallbackStrategy {
         override fun getFont(weight: Fonts.Weight): List<ByteArray> {
           val requestedWeight = weight.weight
           val specs = synchronized(fontsByWeight) {
@@ -120,7 +125,11 @@ class HybridRiveFontConfig : HybridRiveFontConfigSpec() {
           }
         }
       }
-      resetFontCache()
+      synchronized(pickerLock) {
+        strongStylePicker = picker
+        FontFallbackStrategy.stylePicker = picker
+        resetFontCache()
+      }
     }
   }
 
@@ -129,8 +138,11 @@ class HybridRiveFontConfig : HybridRiveFontConfigSpec() {
       synchronized(fontsByWeight) {
         fontsByWeight.clear()
       }
-      FontFallbackStrategy.stylePicker = null
-      resetFontCache()
+      synchronized(pickerLock) {
+        FontFallbackStrategy.stylePicker = null
+        strongStylePicker = null
+        resetFontCache()
+      }
     }
   }
 }

example/src/reproducers/Issue369FontPickerGC.tsx

@@ -0,0 +1,168 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import {
+  View,
+  Text,
+  StyleSheet,
+  Pressable,
+  ActivityIndicator,
+} from 'react-native';
+import {
+  Fit,
+  RiveView,
+  RiveFonts,
+  useRive,
+  useRiveFile,
+  useRiveString,
+  useViewModelInstance,
+} from '@rive-app/react-native';
+import { type Metadata } from '../shared/metadata';
+
+/**
+ * Issue #369: on Android, rive-android keeps the fallback-font picker only in a
+ * WeakReference. If a GC runs between setFallbackFonts() and the first text
+ * that needs a fallback, the picker is gone and non-Latin text renders blank.
+ *
+ * Start sets Kanit (Thai) as the fallback font, loads it again CHURN_LOADS
+ * times to make the Java heap collect, then mounts a view showing Thai text.
+ * Expected: the Thai text renders in Kanit.
+ */
+
+const FONT = 'kanit_regular.ttf';
+const THAI = 'สวัสดี โลก';
+const CHURN_LOADS = 250;
+
+type Phase = 'idle' | 'churning' | 'mounted';
+
+let fontOps: Promise<unknown> = Promise.resolve();
+
+// Fallback fonts are global native state, so set/clear must not interleave across runs.
+function serializeFontOp<T>(op: () => Promise<T>): Promise<T> {
+  const next = fontOps.then(op);
+  fontOps = next.catch(() => {});
+  return next;
+}
+
+export default function Issue369FontPickerGC() {
+  const [phase, setPhase] = useState<Phase>('idle');
+  const [churned, setChurned] = useState(0);
+  const runId = useRef(0);
+
+  const start = useCallback(async () => {
+    const id = ++runId.current;
+    const isCurrent = () => runId.current === id;
+    setChurned(0);
+    const kanit = await RiveFonts.loadFont(FONT);
+    if (!isCurrent()) return;
+    await serializeFontOp(async () => {
+      if (isCurrent()) await RiveFonts.setFallbackFonts({ default: [kanit] });
+    });
+    if (!isCurrent()) return;
+    setPhase('churning');
+    for (let i = 1; i <= CHURN_LOADS; i++) {
+      await RiveFonts.loadFont(FONT);
+      if (!isCurrent()) return;
+      if (i % 10 === 0) setChurned(i);
+    }
+    setChurned(CHURN_LOADS);
+    setPhase('mounted');
+  }, []);
+
+  const cancel = useCallback(() => ++runId.current, []);
+
+  const reset = useCallback(async () => {
+    const id = cancel();
+    setPhase('idle');
+    setChurned(0);
+    await serializeFontOp(() => RiveFonts.clearFallbackFonts());
+    return id;
+  }, [cancel]);
+
+  const restart = useCallback(async () => {
+    const id = await reset();
+    if (runId.current === id) start();
+  }, [reset, start]);
+
+  useEffect(() => {
+    start();
+    return () => {
+      cancel();
+      serializeFontOp(() => RiveFonts.clearFallbackFonts());
+    };
+  }, [start, cancel]);
+
+  return (
+    <View style={styles.container}>
+      <View style={styles.riveContainer}>
+        {phase === 'mounted' ? <ThaiText /> : null}
+      </View>
+      <Text style={styles.status}>
+        phase: {phase} · churned {churned}/{CHURN_LOADS}
+      </Text>
+      <Text style={styles.hint}>
+        Expected: "{THAI}" renders in the Rive view above. Blank means the
+        fallback picker was garbage-collected.
+      </Text>
+      <View style={styles.buttons}>
+        <Pressable style={styles.button} onPress={restart}>
+          <Text style={styles.buttonText}>Start</Text>
+        </Pressable>
+        <Pressable style={styles.button} onPress={reset}>
+          <Text style={styles.buttonText}>Reset</Text>
+        </Pressable>
+      </View>
+    </View>
+  );
+}
+
+function ThaiText() {
+  const { riveViewRef, setHybridRef } = useRive();
+  const { riveFile } = useRiveFile(
+    require('../../assets/rive/font_fallback.riv')
+  );
+  const { instance } = useViewModelInstance(riveFile, { async: true });
+  const { setValue } = useRiveString('text', instance);
+
+  useEffect(() => {
+    setValue(THAI);
+    riveViewRef?.playIfNeeded();
+  }, [setValue, riveViewRef]);
+
+  if (!riveFile || !instance) {
+    return <ActivityIndicator size="large" />;
+  }
+  return (
+    <RiveView
+      hybridRef={setHybridRef}
+      file={riveFile}
+      dataBind={instance}
+      fit={Fit.Contain}
+      style={StyleSheet.absoluteFill}
+    />
+  );
+}
+
+Issue369FontPickerGC.metadata = {
+  name: 'Issue #369: fallback font picker GC',
+  description: 'Android fallback fonts stop working after a garbage collection',
+} satisfies Metadata;
+
+const styles = StyleSheet.create({
+  container: { flex: 1, backgroundColor: '#fff', padding: 16 },
+  riveContainer: {
+    height: 200,
+    backgroundColor: '#222',
+    borderRadius: 8,
+    justifyContent: 'center',
+    overflow: 'hidden',
+  },
+  status: { marginTop: 16, fontSize: 14, fontFamily: 'monospace' },
+  hint: { marginTop: 8, fontSize: 13, color: '#666' },
+  buttons: { flexDirection: 'row', gap: 12, marginTop: 16 },
+  button: {
+    backgroundColor: '#007AFF',
+    paddingHorizontal: 20,
+    paddingVertical: 10,
+    borderRadius: 8,
+  },
+  buttonText: { color: '#fff', fontWeight: '600' },
+});