Added the ability to set properties in interface builder for FlutterViewController.

Author: gaaclarke

shell/platform/darwin/ios/framework/Headers/FlutterViewController.h

@@ -78,6 +78,14 @@ FLUTTER_EXPORT
                         nibName:(nullable NSString*)nibName
                          bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
 
+/**
+ * Initializer that is called from loading a FlutterViewController from a XIB.
+ *
+ * See also:
+ * https://developer.apple.com/documentation/foundation/nscoding/1416145-initwithcoder?language=objc
+ */
+- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_DESIGNATED_INITIALIZER;
+
 /**
  * Registers a callback that will be invoked when the Flutter view has been rendered.
  * The callback will be fired only once.
@@ -194,6 +202,17 @@ FLUTTER_EXPORT
  */
 @property(nonatomic, readonly) NSObject<FlutterBinaryMessenger>* binaryMessenger;
 
+/**
+ * If the `FlutterViewController` creates a `FlutterEngine`, this property
+ * determines if that `FlutterEngine` has `allowHeadlessExecution` set.
+ *
+ * The intention is that this is used with the XIB.  Otherwise, a
+ * `FlutterEngine` can just be sent to the init methods.
+ *
+ * See also: `-[FlutterEngine initWithName:project:allowHeadlessExecution:]`
+ */
+@property(nonatomic, readonly) BOOL engineAllowHeadlessExecution;
+
 @end
 
 NS_ASSUME_NONNULL_END

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

@@ -111,22 +111,26 @@ - (instancetype)initWithEngine:(FlutterEngine*)engine
   return self;
 }
 
+- (void)sharedSetupWithProject:(nullable FlutterDartProject*)project {
+  _viewOpaque = YES;
+  _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
+  _engine.reset([[FlutterEngine alloc] initWithName:@"io.flutter"
+                                            project:project
+                             allowHeadlessExecution:self.engineAllowHeadlessExecution]);
+  _flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
+  [_engine.get() createShell:nil libraryURI:nil];
+  _engineNeedsLaunch = YES;
+  _ongoingTouches = [[NSMutableSet alloc] init];
+  [self loadDefaultSplashScreenView];
+  [self performCommonViewControllerInitialization];
+}
+
 - (instancetype)initWithProject:(nullable FlutterDartProject*)project
                         nibName:(nullable NSString*)nibName
                          bundle:(nullable NSBundle*)nibBundle {
   self = [super initWithNibName:nibName bundle:nibBundle];
   if (self) {
-    _viewOpaque = YES;
-    _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
-    _engine.reset([[FlutterEngine alloc] initWithName:@"io.flutter"
-                                              project:project
-                               allowHeadlessExecution:NO]);
-    _flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
-    [_engine.get() createShell:nil libraryURI:nil];
-    _engineNeedsLaunch = YES;
-    _ongoingTouches = [[NSMutableSet alloc] init];
-    [self loadDefaultSplashScreenView];
-    [self performCommonViewControllerInitialization];
+    [self sharedSetupWithProject:project];
   }
 
   return self;
@@ -137,7 +141,13 @@ - (instancetype)initWithNibName:(NSString*)nibNameOrNil bundle:(NSBundle*)nibBun
 }
 
 - (instancetype)initWithCoder:(NSCoder*)aDecoder {
-  return [self initWithProject:nil nibName:nil bundle:nil];
+  self = [super initWithCoder:aDecoder];
+  return self;
+}
+
+- (void)awakeFromNib {
+  [super awakeFromNib];
+  [self sharedSetupWithProject:nil];
 }
 
 - (instancetype)init {