fix: re-run transformer on transformerId prop change

android/src/main/java/com/appandflow/transformertextinput/TransformerTextInputDecoratorView.kt

@@ -51,8 +51,38 @@ class TransformerTextInputDecoratorView(
   ) ?: state
 
   fun setTransformerId(newTransformerId: Int) {
+    val previousTransformerId = transformerId
     transformerId = newTransformerId
     lastEventValue = null
+    // When the transformer is swapped after mount, re-run it on the current
+    // text so the displayed value reformats immediately. The initial prop
+    // set is excluded by checking that the previous id was non-zero
+    // (default) and that the backing edit text is attached.
+    if (previousTransformerId != 0 &&
+      previousTransformerId != newTransformerId &&
+      reactEditText != null
+    ) {
+      reapplyTransformer()
+    }
+  }
+
+  private fun reapplyTransformer() {
+    val currentValue = currentValue()
+    val currentSelection = currentSelection()
+    val current = TextState(currentValue, currentSelection)
+    val next = transformTextState(current, true)
+    if (next.value == currentValue && next.selection == currentSelection) {
+      return
+    }
+    isUpdating = true
+    try {
+      if (next.value != currentValue) {
+        applyValue(next.value)
+      }
+      applySelection(next.selection)
+    } finally {
+      isUpdating = false
+    }
   }
 
   override fun onAttachedToWindow() {

example/src/App.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState } from 'react';
+import { useRef, useState } from 'react';
 import {
   View,
   StyleSheet,
@@ -122,18 +122,6 @@ function CurrencyExampleCard() {
   const inputRef = useRef<TransformerTextInputInstance>(null);
   const [currency, setCurrency] = useState<CurrencyCode>('USD');
 
-  // Re-run the transformer on the existing value whenever the currency
-  // changes, so the displayed amount reformats in the new locale/symbol.
-  useEffect(() => {
-    const current = inputRef.current?.getValue() ?? '';
-    if (!current) return;
-    inputRef.current?.update({
-      value: current,
-      selection: { start: current.length, end: current.length },
-      transform: true,
-    });
-  }, [currency]);
-
   const handleSetValue = () => {
     inputRef.current?.update({ value: '1234567', transform: true });
   };

ios/TransformerTextInputDecoratorView.mm

@@ -50,11 +50,39 @@ - (void)updateProps:(Props::Shared const &)props oldProps:(Props::Shared const &
   const auto &oldViewProps = *std::static_pointer_cast<TransformerTextInputDecoratorViewProps const>(_props);
   const auto &newViewProps = *std::static_pointer_cast<TransformerTextInputDecoratorViewProps const>(props);
 
-  if (oldViewProps.transformerId != newViewProps.transformerId) {
+  bool transformerIdChanged = oldViewProps.transformerId != newViewProps.transformerId;
+  if (transformerIdChanged) {
     _transformer = rntti::LookupTransformer(newViewProps.transformerId);
   }
 
   [super updateProps:props oldProps:oldProps];
+
+  // When the transformer is swapped after mount, re-run it on the current
+  // text so the displayed value reformats immediately. The initial prop set
+  // is excluded by checking that the previous id was non-zero (default) and
+  // that the backing text input is attached.
+  if (transformerIdChanged && oldViewProps.transformerId != 0 && _backedTextInput != nil) {
+    [self reapplyTransformer];
+  }
+}
+
+- (void)reapplyTransformer
+{
+  NSString *currentValue = [self currentValue];
+  NSRange currentSelection = [self currentSelection];
+  RNTTITextState current{currentValue, currentSelection};
+  RNTTITextState next = [self transformTextState:current transform:YES];
+  bool didTransformValue = ![next.value isEqualToString:currentValue];
+  if (!didTransformValue && NSEqualRanges(next.selection, currentSelection)) {
+    return;
+  }
+  if (didTransformValue) {
+    [self applyValue:next.value];
+  }
+  [self applySelection:next.selection];
+  if (didTransformValue) {
+    [_baseDelegate textInputDidChange];
+  }
 }
 
 - (void)applyValue:(NSString *)newValue