[webview_flutter_wkwebview] Updates platform views on iOS to only have a weak reference to the native view (#11175)

Updates `PlatformViewImpl` to only store a weak reference to the native view. This [issue](flutter/flutter#168535) seems to indicate the `PlatformViewsController` is keeping a reference to the native view even after it is removed from the `InstanceManager` in `webview_flutter_wkwebview`. This change should allow the pigeon call to happen when the reference to the Dart instance is deallocated. This should be safe because if the Dart instance is deallocated, then the Widget tree should no longer contain the PlatformView. And therefore the native UIView should no longer need to be used. Nor any callbacks that need the `UIView` since it is not on screen.

Potential fix for flutter/flutter#168535, but should still update engine to notify plugins that they are detached before setting `PlatformViewsController` to nil.

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Author: bparrishMines

packages/webview_flutter/webview_flutter_wkwebview/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 3.24.1
+
+* Updates platform views on iOS to only have a weak reference to the native view. This is a
+  potential workaround to prevent a crash during the Flutter engine shutdown. See https://github.com/flutter/flutter/issues/168535
+
 ## 3.24.0
 
 * Adds support for `WebKitWebViewControllerCreationParams.javaScriptCanOpenWindowsAutomatically` to allow JavaScript's

packages/webview_flutter/webview_flutter_wkwebview/darwin/Tests/PlatformViewImplTests.swift

@@ -0,0 +1,25 @@
+// Copyright 2013 The Flutter Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import XCTest
+
+@testable import webview_flutter_wkwebview
+
+#if os(iOS)
+  import UIKit
+#endif
+
+class PlatformViewImplTests: XCTestCase {
+  #if os(iOS)
+    func testPlatformViewImplStoresViewWithAWeakReference() {
+      var view: UIView? = UIView()
+      let platformView = PlatformViewImpl(uiView: view!)
+
+      XCTAssertNotNil(platformView.uiView)
+
+      view = nil
+      XCTAssertNil(platformView.uiView)
+    }
+  #endif
+}

packages/webview_flutter/webview_flutter_wkwebview/darwin/webview_flutter_wkwebview/Sources/webview_flutter_wkwebview/FlutterViewFactory.swift

@@ -13,23 +13,36 @@ import Foundation
   #error("Unsupported platform.")
 #endif
 
-/// Implementation of `FlutterPlatformViewFactory` that retrieves the view from the `WebKitLibraryPigeonInstanceManager`.
-class FlutterViewFactory: NSObject, FlutterPlatformViewFactory {
-  unowned let instanceManager: WebKitLibraryPigeonInstanceManager
-
-  #if os(iOS)
-    class PlatformViewImpl: NSObject, FlutterPlatformView {
-      let uiView: UIView
+#if os(iOS)
+  class PlatformViewImpl: NSObject, FlutterPlatformView {
+    // TODO(bparrishMines): Change to strong reference once this issue is fixed in the engine and
+    // makes it to stable. See https://github.com/flutter/flutter/issues/168535.
+    // The InstanceManager used by pigeon adds an associated object to added instances that makes a message call when
+    // they are deallocated. This sets a weak reference to the underlying UIView to prevent a crash where the UIView is
+    // no longer referenced by the plugin, but the FlutterViewController still maintains a transitive reference to it
+    // when the BinaryMessenger becomes invalid.
+    weak var uiView: UIView?
 
-      init(uiView: UIView) {
-        self.uiView = uiView
-      }
+    init(uiView: UIView) {
+      self.uiView = uiView
+    }
 
-      func view() -> UIView {
+    func view() -> UIView {
+      if let uiView = uiView {
         return uiView
       }
+
+      NSLog(
+        "WebViewFlutterPluginError: UIView has been deallocated, but is still being requested as a PlatformView."
+      )
+      return UIView()
     }
-  #endif
+  }
+#endif
+
+/// Implementation of `FlutterPlatformViewFactory` that retrieves the view from the `WebKitLibraryPigeonInstanceManager`.
+class FlutterViewFactory: NSObject, FlutterPlatformViewFactory {
+  unowned let instanceManager: WebKitLibraryPigeonInstanceManager
 
   init(instanceManager: WebKitLibraryPigeonInstanceManager) {
     self.instanceManager = instanceManager
@@ -42,14 +55,9 @@ class FlutterViewFactory: NSObject, FlutterPlatformViewFactory {
       let identifier: Int64 = args is Int64 ? args as! Int64 : Int64(args as! Int32)
       let instance: AnyObject? = instanceManager.instance(forIdentifier: identifier)
 
-      if let instance = instance as? FlutterPlatformView {
-        instance.view().frame = frame
-        return instance
-      } else {
-        let view = instance as! UIView
-        view.frame = frame
-        return PlatformViewImpl(uiView: view)
-      }
+      let view = instance as! UIView
+      view.frame = frame
+      return PlatformViewImpl(uiView: view)
     }
   #elseif os(macOS)
     func create(

packages/webview_flutter/webview_flutter_wkwebview/pubspec.yaml

@@ -2,7 +2,7 @@ name: webview_flutter_wkwebview
 description: A Flutter plugin that provides a WebView widget based on Apple's WKWebView control.
 repository: https://github.com/flutter/packages/tree/main/packages/webview_flutter/webview_flutter_wkwebview
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 3.24.0
+version: 3.24.1
 
 environment:
   sdk: ^3.9.0