fix(ios): discard stale deferred picker selections

example/src/PickerIOSExample.tsx

@@ -1,5 +1,5 @@
 import * as React from 'react';
-import {Text, StyleSheet, View} from 'react-native';
+import {Button, Text, StyleSheet, View} from 'react-native';
 import {PickerIOS} from '@react-native-picker/picker';
 
 const CAR_MAKES_AND_MODELS = {
@@ -127,6 +127,32 @@ function PickerExample() {
   );
 }
 
+function ControlledPickerRapidUpdatesExample() {
+  const [value, setValue] = React.useState('first');
+
+  return (
+    <View>
+      <Text>Rapidly alternate the two buttons while the wheel is moving.</Text>
+      <Button title="Select first" onPress={() => setValue('first')} />
+      <Button title="Select last" onPress={() => setValue('last')} />
+      <PickerIOS
+        accessibilityLabel="Controlled picker rapid updates reproduction"
+        selectedValue={value}
+        testID="controlled-picker-rapid-updates"
+        onValueChange={(nextValue) => setValue(nextValue)}
+      >
+        <PickerIOS.Item label="First" value="first" />
+        <PickerIOS.Item label="Second" value="second" />
+        <PickerIOS.Item label="Third" value="third" />
+        <PickerIOS.Item label="Last" value="last" />
+      </PickerIOS>
+      <Text testID="controlled-picker-rapid-updates-value">
+        Selected: {value}
+      </Text>
+    </View>
+  );
+}
+
 function PickerStyleExample() {
   const [carMake, setCarMake] = React.useState<string>('cadillac');
 
@@ -156,6 +182,10 @@ export const examples = [
     title: '<PickerIOS>',
     render: PickerExample,
   },
+  {
+    title: '<PickerIOS> with rapid controlled updates',
+    render: ControlledPickerRapidUpdatesExample,
+  },
   {
     title: '<PickerIOS> with custom styling',
     render: PickerStyleExample,

ios/RNCPicker.mm

@@ -14,6 +14,7 @@
 #import <React/RCTUtils.h>
 
 @interface RNCPicker() <UIPickerViewDataSource, UIPickerViewDelegate, UIPickerViewAccessibilityDelegate>
+@property (nonatomic, assign) NSUInteger selectionGeneration;
 @end
 
 @implementation RNCPicker
@@ -39,8 +40,26 @@ - (instancetype)initWithFrame:(CGRect)frame
 
 RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
 
+// Selection is deferred so UIPickerView can finish processing the props update.
+// A native callback or reload may establish a newer selection before this runs.
+- (void)scheduleSelectionOfRow:(NSInteger)row
+                      animated:(BOOL)animated
+                    generation:(NSUInteger)generation
+{
+  dispatch_async(dispatch_get_main_queue(), ^{
+    if (self.selectionGeneration == generation) {
+      [self selectRow:row inComponent:0 animated:animated];
+    }
+  });
+}
+
 - (void)setItems:(NSArray<NSDictionary *> *)items
 {
+  if ([_items isEqualToArray:items]) {
+    return;
+  }
+
+  _selectionGeneration += 1;
   _items = [items copy];
   [self setNeedsLayout];
 }
@@ -50,21 +69,43 @@ - (void)setSelectedIndex:(NSInteger)selectedIndex
   if (_selectedIndex != selectedIndex) {
     BOOL animated = _selectedIndex != NSNotFound; // Don't animate the initial value
     _selectedIndex = selectedIndex;
-    dispatch_async(dispatch_get_main_queue(), ^{
-      [self selectRow:selectedIndex inComponent:0 animated:animated];
-    });
+    NSUInteger selectionGeneration = ++_selectionGeneration;
+    [self scheduleSelectionOfRow:selectedIndex
+                         animated:animated
+                       generation:selectionGeneration];
+  }
+}
+
+- (void)reloadAllComponents
+{
+  // Re-queue the latest known selection after the reload without animation.
+  NSUInteger selectionGeneration = ++_selectionGeneration;
+  [super reloadAllComponents];
+
+  if (_selectedIndex != NSNotFound && _selectedIndex < (NSInteger)_items.count) {
+    [self scheduleSelectionOfRow:_selectedIndex
+                         animated:NO
+                       generation:selectionGeneration];
   }
 }
 
 - (void)setNumberOfLines:(NSInteger)numberOfLines
 {
+  if (_numberOfLines == numberOfLines) {
+    return;
+  }
+
   _numberOfLines = numberOfLines;
   [self reloadAllComponents];
   [self setNeedsLayout];
 }
 
 - (void) setFont:(UIFont *)font
 {
+  if ([_font isEqual:font]) {
+    return;
+  }
+
   _font = font;
   [self reloadAllComponents];
   [self setNeedsLayout];
@@ -135,6 +176,7 @@ - (UIView *)pickerView:(UIPickerView *)pickerView
 - (void)pickerView:(__unused UIPickerView *)pickerView
       didSelectRow:(NSInteger)row inComponent:(__unused NSInteger)component
 {
+  _selectionGeneration += 1;
   _selectedIndex = row;
   if (_onChange && _items.count > (NSUInteger)row) {
     _onChange(@{
@@ -162,6 +204,7 @@ - (void)pickerView:(__unused UIPickerView *)pickerView
       didSelectRow:(NSInteger)row inComponent:(__unused NSInteger)component
   withEventEmitter:(facebook::react::SharedViewEventEmitter)eventEmitter
 {
+    _selectionGeneration += 1;
     _selectedIndex = row;
       if (eventEmitter != nullptr && _items.count > (NSUInteger)row) {
           std::dynamic_pointer_cast<const facebook::react::RNCPickerEventEmitter>(eventEmitter)