message: [SwitchBoard] Refactor to not create unused strings.
diff: #import <React/UIView+React.h>
  #import <React/RCTRootView.h>
  +// Invoked on the main thread.
  +typedef void(^ARSwitchBoardPresentInternalViewController)(UIViewController * _Nonnull fromViewController);
  +
  @implementation ARSwitchBoardModule
  @synthesize bridge = _bridge;
  @@ -24,12 +27,14 @@ RCT_EXPORT_METHOD(presentModalViewController:(nonnull NSNumber *)reactTag route:
  RCT_EXPORT_METHOD(dismissModalViewController:(nonnull NSNumber *)reactTag)
  {
  - [self invokeCallback:^(UIViewController *vc, NSString *_) { [vc dismissViewControllerAnimated:YES completion:nil]; } reactTag:reactTag];
  + [self invokeCallback:^(UIViewController *fromViewController) {
  + [fromViewController dismissViewControllerAnimated:YES completion:nil];
  + } reactTag:reactTag];
  }
  RCT_EXPORT_METHOD(presentMediaPreviewController:(nonnull NSNumber *)reactTag route:(nonnull NSURL *)route cacheKey:(nullable NSString *)cacheKey fileExtension:(nullable NSString *)fileExtension)
  {
  - [self invokeCallback:^(UIViewController *fromViewController, id _) {
  + [self invokeCallback:^(UIViewController *fromViewController) {
  ARMediaPreviewController *previewController = [[ARMediaPreviewController alloc] initWithRemoteURL:route
  cacheKey:cacheKey
  fileExtension:fileExtension];
  @@ -49,6 +54,14 @@ RCT_EXPORT_METHOD(presentMediaPreviewController:(nonnull NSNumber *)reactTag rou
  - (void)invokeCallback:(ARSwitchBoardPresentViewController)callback
  reactTag:(nonnull NSNumber *)reactTag
  route:(nonnull NSString *)route;
  +{
  + [self invokeCallback:^(UIViewController * _Nonnull fromViewController) {
  + callback(fromViewController, route);
  + } reactTag:reactTag];
  +}
  +
  +- (void)invokeCallback:(ARSwitchBoardPresentInternalViewController)callback
  + reactTag:(nonnull NSNumber *)reactTag
  {
  UIView *rootView = [self.bridge.uiManager viewForReactTag:reactTag];
  while (rootView.superview && ![rootView isKindOfClass:RCTRootView.class]) {
  @@ -56,13 +69,7 @@ RCT_EXPORT_METHOD(presentMediaPreviewController:(nonnull NSNumber *)reactTag rou
  }
  UIViewController *viewController = rootView.reactViewController;
  NSParameterAssert(viewController);
  - callback(viewController, route);
  -}
  -
  -- (void)invokeCallback:(ARSwitchBoardPresentViewController)callback
  - reactTag:(nonnull NSNumber *)reactTag
  -{
  - [self invokeCallback:callback reactTag:reactTag route:@""];
  + callback(viewController);
  }
  @end
  