SystemNavigator.pop can pop w/o UINavigationController (flutter/engine#6341)

* SystemNavigator.pop can pop w/o UINavigationController

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

@@ -5,10 +5,15 @@
 #ifndef SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERPLATFORMPLUGIN_H_
 #define SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERPLATFORMPLUGIN_H_
 
+#include "flutter/fml/memory/weak_ptr.h"
 #include "flutter/shell/platform/darwin/ios/framework/Headers/FlutterChannels.h"
 
-@interface FlutterPlatformPlugin : NSObject
+#include <UIKit/UIKit.h>
 
+@interface FlutterPlatformPlugin : NSObject
+- (instancetype)init NS_UNAVAILABLE;
+- (instancetype)initWithViewController:(fml::WeakPtr<UIViewController>)viewController
+    NS_DESIGNATED_INITIALIZER;
 - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result;
 
 @end

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

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.h"
+#include "flutter/fml/logging.h"
 
 #include <AudioToolbox/AudioToolbox.h>
 #include <Foundation/Foundation.h>
@@ -31,7 +32,26 @@ const char* const kOverlayStyleUpdateNotificationKey =
 
 using namespace shell;
 
-@implementation FlutterPlatformPlugin
+@implementation FlutterPlatformPlugin {
+  fml::WeakPtr<UIViewController> _viewController;
+}
+
+- (instancetype)init {
+  @throw([NSException exceptionWithName:@"FlutterPlatformPlugin must initWithViewController"
+                                 reason:nil
+                               userInfo:nil]);
+}
+
+- (instancetype)initWithViewController:(fml::WeakPtr<UIViewController>)viewController {
+  FML_DCHECK(viewController) << "viewController must be set";
+  self = [super init];
+
+  if (self) {
+    _viewController = viewController;
+  }
+
+  return self;
+}
 
 - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
   NSString* method = call.method;
@@ -178,9 +198,13 @@ using namespace shell;
   // Apple's human user guidelines say not to terminate iOS applications. However, if the
   // root view of the app is a navigation controller, it is instructed to back up a level
   // in the navigation hierarchy.
+  // It's also possible in an Add2App scenario that the FlutterViewController was presented
+  // outside the context of a UINavigationController, and still wants to be popped.
   UIViewController* viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
   if ([viewController isKindOfClass:[UINavigationController class]]) {
     [((UINavigationController*)viewController) popViewControllerAnimated:NO];
+  } else if (viewController != _viewController.get()) {
+    [_viewController.get() dismissViewControllerAnimated:NO completion:nil];
   }
 }
 

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

@@ -8,6 +8,7 @@
 
 #include <memory>
 
+#include "flutter/fml/memory/weak_ptr.h"
 #include "flutter/fml/message_loop.h"
 #include "flutter/fml/platform/darwin/platform_version.h"
 #include "flutter/fml/platform/darwin/scoped_nsobject.h"
@@ -34,6 +35,7 @@
   fml::scoped_nsobject<FlutterDartProject> _dartProject;
   shell::ThreadHost _threadHost;
   std::unique_ptr<shell::Shell> _shell;
+  std::unique_ptr<fml::WeakPtrFactory<FlutterViewController>> _weakFactory;
 
   // Channels
   fml::scoped_nsobject<FlutterPlatformPlugin> _platformPlugin;
@@ -65,6 +67,7 @@
                          bundle:(NSBundle*)nibBundleOrNil {
   self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
   if (self) {
+    _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
     if (projectOrNil == nil)
       _dartProject.reset([[FlutterDartProject alloc] init]);
     else
@@ -209,7 +212,8 @@
       binaryMessenger:self
                 codec:[FlutterJSONMessageCodec sharedInstance]]);
 
-  _platformPlugin.reset([[FlutterPlatformPlugin alloc] init]);
+  _platformPlugin.reset(
+      [[FlutterPlatformPlugin alloc] initWithViewController:_weakFactory->GetWeakPtr()]);
   [_platformChannel.get() setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
     [_platformPlugin.get() handleMethodCall:call result:result];
   }];