[iOS] [Fixed] - Revert [previous incomplete fix](https://github.com/facebook/react-native/commit/bd2b7d6c0366b5f19de56b71cb706a0af4b0be43) for [an issue](https://github.com/facebook/react-native/issues/26473) with Modal’s onDismiss prop.

This reverts commit bd2b7d6c03.

Libraries/Modal/Modal.js

@@ -12,8 +12,11 @@
 
 const AppContainer = require('../ReactNative/AppContainer');
 const I18nManager = require('../ReactNative/I18nManager');
-const PropTypes = require('prop-types');
+const NativeEventEmitter = require('../EventEmitter/NativeEventEmitter');
+import NativeModalManager from './NativeModalManager';
+const Platform = require('../Utilities/Platform');
 const React = require('react');
+const PropTypes = require('prop-types');
 const ScrollView = require('../Components/ScrollView/ScrollView');
 const StyleSheet = require('../StyleSheet/StyleSheet');
 const View = require('../Components/View/View');
@@ -22,6 +25,12 @@ import type {ViewProps} from '../Components/View/ViewPropTypes';
 import type {DirectEventHandler} from '../Types/CodegenTypes';
 import type EmitterSubscription from '../vendor/emitter/EmitterSubscription';
 import RCTModalHostView from './RCTModalHostViewNativeComponent';
+
+const ModalEventEmitter =
+  Platform.OS === 'ios' && NativeModalManager != null
+    ? new NativeEventEmitter(NativeModalManager)
+    : null;
+
 /**
  * The Modal component is a simple way to present content above an enclosing view.
  *
@@ -178,9 +187,22 @@ class Modal extends React.Component<Props> {
     };
   }
 
+  componentDidMount() {
+    if (ModalEventEmitter) {
+      this._eventSubscription = ModalEventEmitter.addListener(
+        'modalDismissed',
+        event => {
+          if (event.modalID === this._identifier && this.props.onDismiss) {
+            this.props.onDismiss();
+          }
+        },
+      );
+    }
+  }
+
   componentWillUnmount() {
-    if (this.props.onDismiss != null) {
-      this.props.onDismiss();
+    if (this._eventSubscription) {
+      this._eventSubscription.remove();
     }
   }
 

Libraries/Modal/RCTModalHostViewNativeComponent.js

@@ -86,6 +86,14 @@ type NativeProps = $ReadOnly<{|
    */
   onShow?: ?DirectEventHandler<null>,
 
+  /**
+   * The `onDismiss` prop allows passing a function that will be called once
+   * the modal has been dismissed.
+   *
+   * See https://facebook.github.io/react-native/docs/modal.html#ondismiss
+   */
+  onDismiss?: ?BubblingEventHandler<null>,
+
   /**
    * Deprecated. Use the `animationType` prop instead.
    */

React/Views/RCTModalHostViewManager.m

@@ -10,6 +10,7 @@
 #import "RCTBridge.h"
 #import "RCTModalHostView.h"
 #import "RCTModalHostViewController.h"
+#import "RCTModalManager.h"
 #import "RCTShadowView.h"
 #import "RCTUtils.h"
 
@@ -80,10 +81,15 @@ RCT_EXPORT_MODULE()
 
 - (void)dismissModalHostView:(RCTModalHostView *)modalHostView withViewController:(RCTModalHostViewController *)viewController animated:(BOOL)animated
 {
+  dispatch_block_t completionBlock = ^{
+    if (modalHostView.identifier) {
+      [[self.bridge moduleForClass:[RCTModalManager class]] modalDismissed:modalHostView.identifier];
+    }
+  };
   if (_dismissalBlock) {
-    _dismissalBlock([modalHostView reactViewController], viewController, animated, nil);
+    _dismissalBlock([modalHostView reactViewController], viewController, animated, completionBlock);
   } else {
-    [viewController.presentingViewController dismissViewControllerAnimated:animated completion:nil];
+    [viewController.presentingViewController dismissViewControllerAnimated:animated completion:completionBlock];
   }
 }
 

React/Views/RCTModalManager.h

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <UIKit/UIKit.h>
+
+#import <React/RCTBridgeModule.h>
+#import <React/RCTEventEmitter.h>
+
+@interface RCTModalManager : RCTEventEmitter <RCTBridgeModule>
+
+- (void)modalDismissed:(NSNumber *)modalID;
+
+@end

React/Views/RCTModalManager.m

@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTModalManager.h"
+
+@interface RCTModalManager ()
+
+@property BOOL shouldEmit;
+
+@end
+
+@implementation RCTModalManager
+
+RCT_EXPORT_MODULE();
+
+- (NSArray<NSString *> *)supportedEvents
+{
+  return @[ @"modalDismissed" ];
+}
+
+- (void)startObserving
+{
+  _shouldEmit = YES;
+}
+
+- (void)stopObserving
+{
+  _shouldEmit = NO;
+}
+
+- (void)modalDismissed:(NSNumber *)modalID
+{
+  if (_shouldEmit) {
+    [self sendEventWithName:@"modalDismissed" body:@{ @"modalID": modalID }];
+  }
+}
+
+@end