Core - FrameHandler track frame lifecycle

- FrameHandler now tracks frame creation and removal and reuses the IFrame reference
- CefFrameWrapper no longer throws exception if accessing Identifier for invalid frame, this appears
to be a valid use case now which makes sense otherwise we'd never be able to identify the frame.

Resolves #3588

Author: amaitland

CefSharp.Core.Runtime/Internals/CefFrameWrapper.cpp

@@ -311,7 +311,6 @@ String^ CefFrameWrapper::Name::get()
 Int64 CefFrameWrapper::Identifier::get()
 {
     ThrowIfDisposed();
-    ThrowIfFrameInvalid();
 
     return _frame->GetIdentifier();
 }

CefSharp.WinForms.Example/BrowserTabUserControl.cs

@@ -42,6 +42,7 @@ public BrowserTabUserControl(Action<string, int?> openNewTab, string url, bool m
             browser.JsDialogHandler = new JsDialogHandler();
             browser.DownloadHandler = new DownloadHandler();
             browser.AudioHandler = new CefSharp.Handler.AudioHandler();
+            browser.FrameHandler = new CefSharp.Handler.FrameHandler();
 
             if (multiThreadedMessageLoopEnabled)
             {

CefSharp/Handler/FrameHandler.cs

@@ -2,6 +2,8 @@
 //
 // Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
 
+using System.Collections.Generic;
+
 namespace CefSharp.Handler
 {
     /// <summary>
@@ -10,10 +12,16 @@ namespace CefSharp.Handler
     /// </summary>
     public class FrameHandler : IFrameHandler
     {
+        private Dictionary<long, IFrame> frames = new Dictionary<long, IFrame>();
+
         /// <inheritdoc/>
         void IFrameHandler.OnFrameAttached(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
-            OnFrameAttached(chromiumWebBrowser, browser, frame);
+            //If we have a reference to the frame then we'll reuse that for memory management purposes
+            //The frame param massed on here is stack allocated so will be disposed when out of scope.
+            var storedFrame = GetFrameById(frame.Identifier);
+
+            OnFrameAttached(chromiumWebBrowser, browser, storedFrame ?? frame);
         }
 
         /// <summary>
@@ -25,12 +33,14 @@ void IFrameHandler.OnFrameAttached(IWebBrowser chromiumWebBrowser, IBrowser brow
         /// <param name="frame">the frame object</param>
         protected virtual void OnFrameAttached(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
-
+            
         }
 
         /// <inheritdoc/>
         void IFrameHandler.OnFrameCreated(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
+            frames.Add(frame.Identifier, frame);
+
             OnFrameCreated(chromiumWebBrowser, browser, frame);
         }
 
@@ -45,12 +55,14 @@ void IFrameHandler.OnFrameCreated(IWebBrowser chromiumWebBrowser, IBrowser brows
         /// <param name="frame">the frame object</param>
         protected virtual void OnFrameCreated(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
-
+            
         }
 
         /// <inheritdoc/>
         void IFrameHandler.OnFrameDetached(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
+            frames.Remove(frame.Identifier);
+
             OnFrameDetached(chromiumWebBrowser, browser, frame);
         }
 
@@ -66,13 +78,17 @@ void IFrameHandler.OnFrameDetached(IWebBrowser chromiumWebBrowser, IBrowser brow
         /// <param name="frame">the frame object</param>
         protected virtual void OnFrameDetached(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame)
         {
-
+            
         }
 
         /// <inheritdoc/>
         void IFrameHandler.OnMainFrameChanged(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame oldFrame, IFrame newFrame)
         {
-            OnMainFrameChanged(chromiumWebBrowser, browser, oldFrame, newFrame);
+            //If we have a reference to the frame then we'll reuse that for memory management purposes
+            //The frame param massed on here is stack allocated so will be disposed when out of scope.
+            var storedFrame = newFrame == null ? null : GetFrameById(newFrame.Identifier);
+
+            OnMainFrameChanged(chromiumWebBrowser, browser, oldFrame, storedFrame ?? newFrame);
         }
 
         /// <summary>
@@ -101,5 +117,15 @@ protected virtual void OnMainFrameChanged(IWebBrowser chromiumWebBrowser, IBrows
         {
 
         }
+
+        private IFrame GetFrameById(long frameId)
+        {
+            if(frames.TryGetValue(frameId, out var frame))
+            {
+                return frame;
+            }
+
+            return null;
+        }
     }
 }