added comments

Author: nukeolay

ios/Classes/OpenFilePlugin.m

@@ -5,35 +5,52 @@ @interface OpenFilePlugin ()<UIDocumentInteractionControllerDelegate>
 
 static NSString *const CHANNEL_NAME = @"open_file";
 
+// Returns the root view controller of the app,
+// or nil if the app has no root view controller.
 static UIViewController *RootViewController() {
+  // If the app is running on iOS 13 or higher, then use the new `connectedScenes`
+  // API to get the root view controller of the key window.
   if (@available(iOS 13, *)) {
+    // Get a list of all the connected scenes in the app.
     NSSet *scenes = [[UIApplication sharedApplication] connectedScenes];
+    // Iterate over the scenes and check if each one is a UIWindowScene.
     for (UIScene *scene in scenes) {
       if ([scene isKindOfClass:[UIWindowScene class]]) {
+        // Get a list of all the windows in the scene.
         NSArray *windows = ((UIWindowScene *)scene).windows;
+        // Iterate over the windows and check if each one is the key window.
         for (UIWindow *window in windows) {
           if (window.isKeyWindow) {
+            // Return the root view controller of the key window.
             return window.rootViewController;
           }
         }
       }
     }
+    // If we couldn't find a key window, then return nil.
     return nil;
   } else {
+    // Simply return the root view controller of the key window.
     return [UIApplication sharedApplication].keyWindow.rootViewController;
   }
 }
 
+// Returns the top view controller in a view controller hierarchy.
 static UIViewController *
 TopViewControllerForViewController(UIViewController *viewController) {
+  // If the view controller has a presented view controller, then return the top
+  // view controller in that hierarchy.
   if (viewController.presentedViewController) {
     return TopViewControllerForViewController(
         viewController.presentedViewController);
   }
+  // If the view controller is a navigation controller, then return the top
+  // view controller in the navigation controller's stack.
   if ([viewController isKindOfClass:[UINavigationController class]]) {
     return TopViewControllerForViewController(
         ((UINavigationController *)viewController).visibleViewController);
   }
+  // Otherwise, return the given view controller.
   return viewController;
 }