State Restoration for iOS (flutter/engine#23495)

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -990,6 +990,9 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatfor
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterPluginAppLifeCycleDelegate.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterPluginAppLifeCycleDelegateTest.m
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterPluginAppLifeCycleDelegate_internal.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPluginTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputDelegate.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.mm

engine/src/flutter/shell/platform/darwin/ios/BUILD.gn

@@ -66,6 +66,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterPlatformViews_Internal.h",
     "framework/Source/FlutterPlatformViews_Internal.mm",
     "framework/Source/FlutterPluginAppLifeCycleDelegate.mm",
+    "framework/Source/FlutterRestorationPlugin.h",
+    "framework/Source/FlutterRestorationPlugin.mm",
     "framework/Source/FlutterTextInputDelegate.h",
     "framework/Source/FlutterTextInputPlugin.h",
     "framework/Source/FlutterTextInputPlugin.mm",
@@ -221,6 +223,7 @@ shared_library("ios_test_flutter") {
     "framework/Source/FlutterEngineGroupTest.mm",
     "framework/Source/FlutterEngineTest.mm",
     "framework/Source/FlutterPluginAppLifeCycleDelegateTest.m",
+    "framework/Source/FlutterRestorationPluginTest.mm",
     "framework/Source/FlutterTextInputPluginTest.m",
     "framework/Source/FlutterViewControllerTest.mm",
     "framework/Source/SemanticsObjectTest.mm",

engine/src/flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngine.h

@@ -135,7 +135,31 @@ FLUTTER_EXPORT
  */
 - (instancetype)initWithName:(NSString*)labelPrefix
                      project:(nullable FlutterDartProject*)project
-      allowHeadlessExecution:(BOOL)allowHeadlessExecution NS_DESIGNATED_INITIALIZER;
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution;
+
+/**
+ * Initialize this FlutterEngine with a `FlutterDartProject`.
+ *
+ * If the FlutterDartProject is not specified, the FlutterEngine will attempt to locate
+ * the project in a default location (the flutter_assets folder in the iOS application
+ * bundle).
+ *
+ * A newly initialized engine will not run the `FlutterDartProject` until either
+ * `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI:` is called.
+ *
+ * @param labelPrefix The label prefix used to identify threads for this instance. Should
+ *   be unique across FlutterEngine instances, and is used in instrumentation to label
+ *   the threads used by this FlutterEngine.
+ * @param project The `FlutterDartProject` to run.
+ * @param allowHeadlessExecution Whether or not to allow this instance to continue
+ *   running after passing a nil `FlutterViewController` to `-setViewController:`.
+ * @param restorationEnabled Whether state restoration is enabled. When true, the framework will
+ *   wait for the attached view controller to provide restoration data.
+ */
+- (instancetype)initWithName:(NSString*)labelPrefix
+                     project:(nullable FlutterDartProject*)project
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution
+          restorationEnabled:(BOOL)restorationEnabled NS_DESIGNATED_INITIALIZER;
 
 + (instancetype)new NS_UNAVAILABLE;
 
@@ -273,6 +297,16 @@ FLUTTER_EXPORT
  */
 @property(nonatomic, readonly) FlutterMethodChannel* navigationChannel;
 
+/**
+ * The `FlutterMethodChannel` used for restoration related platform messages.
+ *
+ * Can be nil after `destroyContext` is called.
+ *
+ * @see [Restoration
+ * Channel](https://api.flutter.dev/flutter/services/SystemChannels/restoration-constant.html)
+ */
+@property(nonatomic, readonly) FlutterMethodChannel* restorationChannel;
+
 /**
  * The `FlutterMethodChannel` used for core platform messages, such as
  * information about the screen orientation.

engine/src/flutter/shell/platform/darwin/ios/framework/Headers/FlutterHeadlessDartRunner.h

@@ -34,7 +34,7 @@ FLUTTER_DEPRECATED("FlutterEngine should be used rather than FlutterHeadlessDart
 @interface FlutterHeadlessDartRunner : FlutterEngine
 
 /**
- * Iniitalize this FlutterHeadlessDartRunner with a `FlutterDartProject`.
+ * Initialize this FlutterHeadlessDartRunner with a `FlutterDartProject`.
  *
  * If the FlutterDartProject is not specified, the FlutterHeadlessDartRunner will attempt to locate
  * the project in a default location.
@@ -49,7 +49,7 @@ FLUTTER_DEPRECATED("FlutterEngine should be used rather than FlutterHeadlessDart
 - (instancetype)initWithName:(NSString*)labelPrefix project:(FlutterDartProject*)projectOrNil;
 
 /**
- * Iniitalize this FlutterHeadlessDartRunner with a `FlutterDartProject`.
+ * Initialize this FlutterHeadlessDartRunner with a `FlutterDartProject`.
  *
  * If the FlutterDartProject is not specified, the FlutterHeadlessDartRunner will attempt to locate
  * the project in a default location.
@@ -64,7 +64,27 @@ FLUTTER_DEPRECATED("FlutterEngine should be used rather than FlutterHeadlessDart
  */
 - (instancetype)initWithName:(NSString*)labelPrefix
                      project:(FlutterDartProject*)projectOrNil
-      allowHeadlessExecution:(BOOL)allowHeadlessExecution NS_DESIGNATED_INITIALIZER;
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution;
+
+/**
+ * Initialize this FlutterHeadlessDartRunner with a `FlutterDartProject`.
+ *
+ * If the FlutterDartProject is not specified, the FlutterHeadlessDartRunner will attempt to locate
+ * the project in a default location.
+ *
+ * A newly initialized engine will not run the `FlutterDartProject` until either
+ * `-runWithEntrypoint:` or `-runWithEntrypoint:libraryURI` is called.
+ *
+ * @param labelPrefix The label prefix used to identify threads for this instance. Should
+ * be unique across FlutterEngine instances
+ * @param projectOrNil The `FlutterDartProject` to run.
+ * @param allowHeadlessExecution Must be set to `YES`.
+ * @param restorationEnabled Must be set to `NO`.
+ */
+- (instancetype)initWithName:(NSString*)labelPrefix
+                     project:(FlutterDartProject*)projectOrNil
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution
+          restorationEnabled:(BOOL)restorationEnabled NS_DESIGNATED_INITIALIZER;
 
 /**
  * Not recommended for use - will initialize with a default label ("io.flutter.headless")

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterAppDelegate.mm

@@ -11,9 +11,10 @@
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPluginAppLifeCycleDelegate_internal.h"
 
-static NSString* kUIBackgroundMode = @"UIBackgroundModes";
-static NSString* kRemoteNotificationCapabitiliy = @"remote-notification";
-static NSString* kBackgroundFetchCapatibility = @"fetch";
+static NSString* const kUIBackgroundMode = @"UIBackgroundModes";
+static NSString* const kRemoteNotificationCapabitiliy = @"remote-notification";
+static NSString* const kBackgroundFetchCapatibility = @"fetch";
+static NSString* const kRestorationStateAppModificationKey = @"mod-date";
 
 @interface FlutterAppDelegate ()
 @property(nonatomic, copy) FlutterViewController* (^rootFlutterViewControllerGetter)(void);
@@ -308,4 +309,37 @@ static BOOL IsDeepLinkingEnabled(NSDictionary* infoDictionary) {
   }
 }
 
+#pragma mark - State Restoration
+
+- (BOOL)application:(UIApplication*)application shouldSaveApplicationState:(NSCoder*)coder {
+  [coder encodeInt64:self.lastAppModificationTime forKey:kRestorationStateAppModificationKey];
+  return YES;
+}
+
+- (BOOL)application:(UIApplication*)application shouldRestoreApplicationState:(NSCoder*)coder {
+  int64_t stateDate = [coder decodeInt64ForKey:kRestorationStateAppModificationKey];
+  return self.lastAppModificationTime == stateDate;
+}
+
+- (BOOL)application:(UIApplication*)application shouldSaveSecureApplicationState:(NSCoder*)coder {
+  [coder encodeInt64:self.lastAppModificationTime forKey:kRestorationStateAppModificationKey];
+  return YES;
+}
+
+- (BOOL)application:(UIApplication*)application
+    shouldRestoreSecureApplicationState:(NSCoder*)coder {
+  int64_t stateDate = [coder decodeInt64ForKey:kRestorationStateAppModificationKey];
+  return self.lastAppModificationTime == stateDate;
+}
+
+- (int64_t)lastAppModificationTime {
+  NSDate* fileDate;
+  NSError* error = nil;
+  [[[NSBundle mainBundle] executableURL] getResourceValue:&fileDate
+                                                   forKey:NSURLContentModificationDateKey
+                                                    error:&error];
+  NSAssert(error == nil, @"Cannot obtain modification date of main bundle: %@", error);
+  return [fileDate timeIntervalSince1970];
+}
+
 @end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -71,8 +71,10 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
   // Channels
   fml::scoped_nsobject<FlutterPlatformPlugin> _platformPlugin;
   fml::scoped_nsobject<FlutterTextInputPlugin> _textInputPlugin;
+  fml::scoped_nsobject<FlutterRestorationPlugin> _restorationPlugin;
   fml::scoped_nsobject<FlutterMethodChannel> _localizationChannel;
   fml::scoped_nsobject<FlutterMethodChannel> _navigationChannel;
+  fml::scoped_nsobject<FlutterMethodChannel> _restorationChannel;
   fml::scoped_nsobject<FlutterMethodChannel> _platformChannel;
   fml::scoped_nsobject<FlutterMethodChannel> _platformViewsChannel;
   fml::scoped_nsobject<FlutterMethodChannel> _textInputChannel;
@@ -84,6 +86,7 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
   int64_t _nextTextureId;
 
   BOOL _allowHeadlessExecution;
+  BOOL _restorationEnabled;
   FlutterBinaryMessengerRelay* _binaryMessenger;
   std::unique_ptr<flutter::ConnectionCollection> _connections;
 }
@@ -103,10 +106,21 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
 - (instancetype)initWithName:(NSString*)labelPrefix
                      project:(FlutterDartProject*)project
       allowHeadlessExecution:(BOOL)allowHeadlessExecution {
+  return [self initWithName:labelPrefix
+                     project:project
+      allowHeadlessExecution:allowHeadlessExecution
+          restorationEnabled:NO];
+}
+
+- (instancetype)initWithName:(NSString*)labelPrefix
+                     project:(FlutterDartProject*)project
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution
+          restorationEnabled:(BOOL)restorationEnabled {
   self = [super init];
   NSAssert(self, @"Super init cannot be nil");
   NSAssert(labelPrefix, @"labelPrefix is required");
 
+  _restorationEnabled = restorationEnabled;
   _allowHeadlessExecution = allowHeadlessExecution;
   _labelPrefix = [labelPrefix copy];
 
@@ -331,12 +345,18 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
 - (FlutterTextInputPlugin*)textInputPlugin {
   return _textInputPlugin.get();
 }
+- (FlutterRestorationPlugin*)restorationPlugin {
+  return _restorationPlugin.get();
+}
 - (FlutterMethodChannel*)localizationChannel {
   return _localizationChannel.get();
 }
 - (FlutterMethodChannel*)navigationChannel {
   return _navigationChannel.get();
 }
+- (FlutterMethodChannel*)restorationChannel {
+  return _restorationChannel.get();
+}
 - (FlutterMethodChannel*)platformChannel {
   return _platformChannel.get();
 }
@@ -363,6 +383,7 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
 - (void)resetChannels {
   _localizationChannel.reset();
   _navigationChannel.reset();
+  _restorationChannel.reset();
   _platformChannel.reset();
   _platformViewsChannel.reset();
   _textInputChannel.reset();
@@ -413,6 +434,11 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
     _initialRoute = nil;
   }
 
+  _restorationChannel.reset([[FlutterMethodChannel alloc]
+         initWithName:@"flutter/restoration"
+      binaryMessenger:self.binaryMessenger
+                codec:[FlutterStandardMethodCodec sharedInstance]]);
+
   _platformChannel.reset([[FlutterMethodChannel alloc]
          initWithName:@"flutter/platform"
       binaryMessenger:self.binaryMessenger
@@ -452,6 +478,10 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
   _textInputPlugin.get().textInputDelegate = self;
 
   _platformPlugin.reset([[FlutterPlatformPlugin alloc] initWithEngine:[self getWeakPtr]]);
+
+  _restorationPlugin.reset([[FlutterRestorationPlugin alloc]
+         initWithChannel:_restorationChannel.get()
+      restorationEnabled:_restorationEnabled]);
 }
 
 - (void)maybeSetupPlatformViewChannels {

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h

@@ -18,6 +18,7 @@
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputDelegate.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h"
 #import "flutter/shell/platform/darwin/ios/platform_view_ios.h"
@@ -42,6 +43,7 @@ extern NSString* const FlutterEngineWillDealloc;
 - (FlutterPlatformPlugin*)platformPlugin;
 - (std::shared_ptr<flutter::FlutterPlatformViewsController>&)platformViewsController;
 - (FlutterTextInputPlugin*)textInputPlugin;
+- (FlutterRestorationPlugin*)restorationPlugin;
 - (void)launchEngine:(NSString*)entrypoint libraryURI:(NSString*)libraryOrNil;
 - (BOOL)createShell:(NSString*)entrypoint
          libraryURI:(NSString*)libraryOrNil

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterHeadlessDartRunner.mm

@@ -35,10 +35,24 @@
       allowHeadlessExecution:(BOOL)allowHeadlessExecution {
   NSAssert(allowHeadlessExecution == YES,
            @"Cannot initialize a FlutterHeadlessDartRunner without headless execution.");
+  return [self initWithName:labelPrefix
+                     project:projectOrNil
+      allowHeadlessExecution:allowHeadlessExecution
+          restorationEnabled:NO];
+}
+
+- (instancetype)initWithName:(NSString*)labelPrefix
+                     project:(FlutterDartProject*)projectOrNil
+      allowHeadlessExecution:(BOOL)allowHeadlessExecution
+          restorationEnabled:(BOOL)restorationEnabled {
+  NSAssert(allowHeadlessExecution == YES,
+           @"Cannot initialize a FlutterHeadlessDartRunner without headless execution.");
   return [super initWithName:labelPrefix
                      project:projectOrNil
-      allowHeadlessExecution:allowHeadlessExecution];
+      allowHeadlessExecution:allowHeadlessExecution
+          restorationEnabled:restorationEnabled];
 }
+
 - (instancetype)init {
   return [self initWithName:@"io.flutter.headless" project:nil];
 }

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h

@@ -0,0 +1,22 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERRESTORATIONPLUGIN_H_
+#define SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERRESTORATIONPLUGIN_H_
+
+#import <UIKit/UIKit.h>
+
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
+
+@interface FlutterRestorationPlugin : NSObject
+- (instancetype)init NS_UNAVAILABLE;
++ (instancetype)new NS_UNAVAILABLE;
+- (instancetype)initWithChannel:(FlutterMethodChannel*)channel
+             restorationEnabled:(BOOL)waitForData NS_DESIGNATED_INITIALIZER;
+
+@property(nonatomic, strong) NSData* restorationData;
+- (void)markRestorationComplete;
+- (void)reset;
+@end
+#endif  // SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERRESTORATIONPLUGIN_H_

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.mm

@@ -0,0 +1,107 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h"
+
+#import <Foundation/Foundation.h>
+#import <UIKit/UIKit.h>
+
+#include "flutter/fml/logging.h"
+
+FLUTTER_ASSERT_NOT_ARC
+
+@interface FlutterRestorationPlugin ()
+@property(nonatomic, copy) FlutterResult pendingRequest;
+@end
+
+@implementation FlutterRestorationPlugin {
+  BOOL _waitForData;
+  BOOL _restorationEnabled;
+}
+
+- (instancetype)init {
+  @throw([NSException
+      exceptionWithName:@"FlutterRestorationPlugin must initWithChannel:restorationEnabled:"
+                 reason:nil
+               userInfo:nil]);
+}
+
+- (instancetype)initWithChannel:(FlutterMethodChannel*)channel
+             restorationEnabled:(BOOL)restorationEnabled {
+  FML_DCHECK(channel) << "channel must be set";
+  self = [super init];
+  if (self) {
+    [channel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
+      [self handleMethodCall:call result:result];
+    }];
+    _restorationEnabled = restorationEnabled;
+    _waitForData = restorationEnabled;
+  }
+  return self;
+}
+
+- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
+  if ([[call method] isEqualToString:@"put"]) {
+    NSAssert(self.pendingRequest == nil, @"Cannot put data while a get request is pending.");
+    FlutterStandardTypedData* data = [call arguments];
+    self.restorationData = [data data];
+    result(nil);
+  } else if ([[call method] isEqualToString:@"get"]) {
+    if (!_restorationEnabled || !_waitForData) {
+      result([self dataForFramework]);
+      return;
+    }
+    NSAssert(self.pendingRequest == nil, @"There can only be one pending request.");
+    self.pendingRequest = result;
+  } else {
+    result(FlutterMethodNotImplemented);
+  }
+}
+
+- (void)setRestorationData:(NSData*)data {
+  if (data != _restorationData) {
+    [_restorationData release];
+    _restorationData = [data retain];
+  }
+  _waitForData = NO;
+  if (self.pendingRequest != nil) {
+    self.pendingRequest([self dataForFramework]);
+    self.pendingRequest = nil;
+  }
+}
+
+- (void)markRestorationComplete {
+  _waitForData = NO;
+  if (self.pendingRequest != nil) {
+    NSAssert(_restorationEnabled, @"No request can be pending when restoration is disabled.");
+    self.pendingRequest([self dataForFramework]);
+    self.pendingRequest = nil;
+  }
+}
+
+- (void)reset {
+  self.pendingRequest = nil;
+  self.restorationData = nil;
+}
+
+- (NSDictionary*)dataForFramework {
+  if (!_restorationEnabled) {
+    return @{@"enabled" : @NO};
+  }
+  if (self.restorationData == nil) {
+    return @{@"enabled" : @YES};
+  }
+  return @{
+    @"enabled" : @YES,
+    @"data" : [FlutterStandardTypedData typedDataWithBytes:self.restorationData]
+  };
+}
+
+- (void)dealloc {
+  [_restorationData release];
+  [_pendingRequest release];
+  [super dealloc];
+}
+
+@end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPluginTest.mm

@@ -0,0 +1,193 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h"
+
+#import <OCMock/OCMock.h>
+#import <XCTest/XCTest.h>
+
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
+
+FLUTTER_ASSERT_ARC
+
+@interface FlutterRestorationPlugin ()
+- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result;
+@end
+
+@interface FlutterRestorationPluginTest : XCTestCase
+@end
+
+@implementation FlutterRestorationPluginTest {
+  id restorationChannel;
+}
+
+- (void)setUp {
+  [super setUp];
+  restorationChannel = OCMClassMock([FlutterMethodChannel class]);
+}
+
+- (void)tearDown {
+  [restorationChannel stopMocking];
+
+  [super tearDown];
+}
+
+#pragma mark - Tests
+
+- (void)testRestorationEnabledWaitsForData {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  __block id capturedResult;
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertNil(capturedResult);
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  [restorationPlugin setRestorationData:data];
+  XCTAssertEqual([capturedResult count], 2u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+  XCTAssertEqual([[capturedResult objectForKey:@"data"] data], data);
+}
+
+- (void)testRestorationDisabledRespondsRightAway {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:NO];
+
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  __block id capturedResult;
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertEqual([capturedResult count], 1u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @NO);
+}
+
+- (void)testRespondsRightAwayWhenDataIsSet {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  [restorationPlugin setRestorationData:data];
+
+  __block id capturedResult;
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertEqual([capturedResult count], 2u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+  XCTAssertEqual([[capturedResult objectForKey:@"data"] data], data);
+}
+
+- (void)testRespondsWithNoDataWhenRestorationIsCompletedWithoutData {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  __block id capturedResult;
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertNil(capturedResult);
+
+  [restorationPlugin markRestorationComplete];
+  XCTAssertEqual([capturedResult count], 1u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+}
+
+- (void)testRespondsRightAwayWithNoDataWhenRestorationIsCompleted {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+
+  [restorationPlugin markRestorationComplete];
+
+  __block id capturedResult;
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertEqual([capturedResult count], 1u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+}
+
+- (void)testReturnsDataSetByFramework {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+  [restorationPlugin markRestorationComplete];
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  FlutterMethodCall* methodCall = [FlutterMethodCall
+      methodCallWithMethodName:@"put"
+                     arguments:[FlutterStandardTypedData typedDataWithBytes:data]];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 XCTAssertNil(result);
+                               }];
+  XCTAssertEqual([restorationPlugin restorationData], data);
+}
+
+- (void)testRespondsWithDataSetByFramework {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+  [restorationPlugin markRestorationComplete];
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  FlutterMethodCall* methodCall = [FlutterMethodCall
+      methodCallWithMethodName:@"put"
+                     arguments:[FlutterStandardTypedData typedDataWithBytes:data]];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 XCTAssertNil(result);
+                               }];
+  XCTAssertEqual([restorationPlugin restorationData], data);
+
+  __block id capturedResult;
+  methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertEqual([capturedResult count], 2u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+  XCTAssertEqual([[capturedResult objectForKey:@"data"] data], data);
+}
+
+- (void)testResetClearsData {
+  FlutterRestorationPlugin* restorationPlugin =
+      [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];
+  [restorationPlugin markRestorationComplete];
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  FlutterMethodCall* methodCall = [FlutterMethodCall
+      methodCallWithMethodName:@"put"
+                     arguments:[FlutterStandardTypedData typedDataWithBytes:data]];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 XCTAssertNil(result);
+                               }];
+  XCTAssertEqual([restorationPlugin restorationData], data);
+
+  [restorationPlugin reset];
+  XCTAssertNil([restorationPlugin restorationData]);
+
+  __block id capturedResult;
+  methodCall = [FlutterMethodCall methodCallWithMethodName:@"get" arguments:nil];
+  [restorationPlugin handleMethodCall:methodCall
+                               result:^(id _Nullable result) {
+                                 capturedResult = result;
+                               }];
+  XCTAssertEqual([capturedResult count], 1u);
+  XCTAssertEqual([capturedResult objectForKey:@"enabled"], @YES);
+}
+
+@end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -191,7 +191,8 @@ typedef enum UIAccessibilityContrast : NSInteger {
   auto engine = fml::scoped_nsobject<FlutterEngine>{[[FlutterEngine alloc]
                 initWithName:@"io.flutter"
                      project:project
-      allowHeadlessExecution:self.engineAllowHeadlessExecution]};
+      allowHeadlessExecution:self.engineAllowHeadlessExecution
+          restorationEnabled:[self restorationIdentifier] != nil]};
 
   if (!engine) {
     return;
@@ -654,6 +655,7 @@ static void sendFakeTouchEvent(FlutterEngine* engine,
     [self surfaceUpdated:YES];
   }
   [[_engine.get() lifecycleChannel] sendMessage:@"AppLifecycleState.inactive"];
+  [[_engine.get() restorationPlugin] markRestorationComplete];
 
   [super viewWillAppear:animated];
 }
@@ -1523,4 +1525,20 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
   [_engine.get() dispatchPointerDataPacket:std::move(packet)];
 }
 
+#pragma mark - State Restoration
+
+- (void)encodeRestorableStateWithCoder:(NSCoder*)coder {
+  NSData* restorationData = [[_engine.get() restorationPlugin] restorationData];
+  [coder encodeDataObject:restorationData];
+}
+
+- (void)decodeRestorableStateWithCoder:(NSCoder*)coder {
+  NSData* restorationData = [coder decodeDataObject];
+  [[_engine.get() restorationPlugin] setRestorationData:restorationData];
+}
+
+- (FlutterRestorationPlugin*)restorationPlugin {
+  return [_engine.get() restorationPlugin];
+}
+
 @end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h

@@ -8,6 +8,7 @@
 #include "flutter/fml/memory/weak_ptr.h"
 
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterRestorationPlugin.h"
 
 namespace flutter {
 class FlutterPlatformViewsController;
@@ -27,6 +28,7 @@ extern NSNotificationName const FlutterViewControllerShowHomeIndicator;
 @property(nonatomic, readonly) BOOL isPresentingViewController;
 - (fml::WeakPtr<FlutterViewController>)getWeakPtr;
 - (std::shared_ptr<flutter::FlutterPlatformViewsController>&)platformViewsController;
+- (FlutterRestorationPlugin*)restorationPlugin;
 
 @end
 

engine/src/flutter/shell/platform/darwin/ios/platform_view_ios.mm

@@ -207,6 +207,7 @@ void PlatformViewIOS::OnPreEngineRestart() const {
     return;
   }
   [owner_controller_.get() platformViewsController]->Reset();
+  [[owner_controller_.get() restorationPlugin] reset];
 }
 
 std::unique_ptr<std::vector<std::string>> PlatformViewIOS::ComputePlatformResolvedLocales(