[iOS] Fixes state restoration not work

shell/platform/darwin/ios/framework/Source/FlutterRestorationPluginTest.mm

@@ -9,6 +9,8 @@
 
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
+#import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 
 FLUTTER_ASSERT_ARC
 
@@ -36,6 +38,32 @@ - (void)tearDown {
 
 #pragma mark - Tests
 
+- (void)testRestoratonViewControllerEncodeAndDecode {
+  FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"test"
+                                                      project:nil
+                                       allowHeadlessExecution:YES
+                                           restorationEnabled:YES];
+  [engine run];
+  FlutterViewController* flutterViewController =
+      [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
+  FlutterRestorationPlugin* restorationPlugin = flutterViewController.restorationPlugin;
+
+  NSData* data = [@"testrestortiondata" dataUsingEncoding:NSUTF8StringEncoding];
+  [restorationPlugin setRestorationData:data];
+
+  NSKeyedArchiver* archiver = [[NSKeyedArchiver alloc] initRequiringSecureCoding:YES];
+  [flutterViewController encodeRestorableStateWithCoder:archiver];
+
+  [restorationPlugin setRestorationData:nil];
+
+  NSKeyedUnarchiver* unarchiver =
+      [[NSKeyedUnarchiver alloc] initForReadingWithData:archiver.encodedData];
+  [flutterViewController decodeRestorableStateWithCoder:unarchiver];
+
+  XCTAssert([[restorationPlugin restorationData] isEqualToData:data],
+            "Restoration state data must be equal");
+}
+
 - (void)testRestorationEnabledWaitsForData {
   FlutterRestorationPlugin* restorationPlugin =
       [[FlutterRestorationPlugin alloc] initWithChannel:restorationChannel restorationEnabled:YES];

shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -32,6 +32,8 @@
 static constexpr int kMicrosecondsPerSecond = 1000 * 1000;
 static constexpr CGFloat kScrollViewContentSize = 2.0;
 
+static NSString* const kFlutterRestorationStateAppData = @"FlutterRestorationStateAppData";
+
 NSNotificationName const FlutterSemanticsUpdateNotification = @"FlutterSemanticsUpdate";
 NSNotificationName const FlutterViewControllerWillDealloc = @"FlutterViewControllerWillDealloc";
 NSNotificationName const FlutterViewControllerHideHomeIndicator =
@@ -1811,12 +1813,17 @@ - (void)scrollEvent:(UIPanGestureRecognizer*)recognizer API_AVAILABLE(ios(13.4))
 
 - (void)encodeRestorableStateWithCoder:(NSCoder*)coder {
   NSData* restorationData = [[_engine.get() restorationPlugin] restorationData];
-  [coder encodeDataObject:restorationData];
+  [coder encodeBytes:(const unsigned char*)restorationData.bytes
+              length:restorationData.length
+              forKey:kFlutterRestorationStateAppData];
   [super encodeRestorableStateWithCoder:coder];
 }
 
 - (void)decodeRestorableStateWithCoder:(NSCoder*)coder {
-  NSData* restorationData = [coder decodeDataObject];
+  NSUInteger restorationDataLength;
+  const unsigned char* restorationBytes = [coder decodeBytesForKey:kFlutterRestorationStateAppData
+                                                    returnedLength:&restorationDataLength];
+  NSData* restorationData = [NSData dataWithBytes:restorationBytes length:restorationDataLength];
   [[_engine.get() restorationPlugin] setRestorationData:restorationData];
 }