Using CEFSharp ILifeSpanHandler interface to Handle Popups - cefsharp

Question

I have an issue with handling popups. I have implemented ILifeSpanHandler and OnBeforeBrowse (amoungst others) from the IRequestHandler.
How do I know in the ILifeSpanHandler what URL is being called? I am unable to get it in either the OnAfterCreated or OnBeforePopup. Currently I see it first in OnBeforeBrowse.
I have no code as my question is a "How to". In OnBeforePopup I have checked targetUrl however it seems to be there for decoration as I have read that it is not implemented anyway. I have also looked at the browner/chromiumWebBrowser objects, browser and newBroswer seem to be nothing. One would expect in OnAfterCreated chromiumWebBrowser would return an object but it is nothing in my case.
I am testing with the following
Public Sub OnAfterCreated(chromiumWebBrowser As IWebBrowser, browser As IBrowser) Implements ILifeSpanHandler.OnAfterCreated
Try
Debug.Print(vbNewLine)
Debug.Print("OnAfterCreated")
Debug.Print(String.Concat("OnAfterCreated - MainFrame.Url "), browser.MainFrame.Url)
Debug.Print("OnAfterCreated")
Debug.Print(vbNewLine)
Catch ex As Exception
End Try
End Sub
And I have the following
Public Function OnBeforePopup(chromiumWebBrowser As IWebBrowser, browser As IBrowser, frame As IFrame, targetUrl As String, targetFrameName As String, targetDisposition As WindowOpenDisposition, userGesture As Boolean, popupFeatures As IPopupFeatures, windowInfo As IWindowInfo, browserSettings As IBrowserSettings, ByRef noJavascriptAccess As Boolean, ByRef newBrowser As IWebBrowser) As Boolean Implements ILifeSpanHandler.OnBeforePopup
Try
Debug.Print(vbNewLine)
Debug.Print("OnBeforePopup")
Debug.Print(String.Concat("OnBeforePopup - targetUrl "), targetUrl)
Debug.Print(String.Concat("OnBeforePopup - browser.MainFrame.Url "), browser.MainFrame.Url)
Debug.Print(String.Concat("OnBeforePopup - chromiumWebBrowser.Address "), chromiumWebBrowser.Address)
Debug.Print("OnBeforePopup")
Debug.Print(vbNewLine)
Catch ex As Exception
End Try
Return False
End Function

Answer 1

I have seen different approaches in handling popups using ILifeSpanHandler interface. One approach that I've seen also here in Stack Overflow and was accepted as the correct answer to that particular question is to return true in the OnBeforePopup implementation of ILifeSpanHandler then pass the targetURL argument to a handler that creates the popup.
This approach is very unideal because you are destroying the link between the page that actually opened the popup and the popup itself. If you access via JavaScript the opener property of the window object inside the popup you would notice that it is null. And the page that opened the popup would never know that the popup was actually opened because returning true cancels the creation.
The other approach is to let Cef create the popup and the programmer just decides whether to show the browser as a popup window or a child to control (like in tabbed browsing). This is error-free and almost ideal. But the problem with this approach is that you are not able to listen to events such as FrameLoadStart, FrameLoadEnd, AddressChanged, TitleChanged, etc.
One approach that is tagged experimental by the Cef developers is to return a new IWebBrowser instance via newWebBrowser out parameter. This has so many many side effects. The page that opened the popup would, of course, recognize the popup as his although it was not the original browser (IBrowser) that it created. The page may just ignore it like btcclicks.com and in that case, there'd be no problem. But there are websites like drops.xyz that is so particular with his stuff and will discard everything that is not originally his. So this is a problem.
So what is the correct approach?
The ChromeWebBrowser control
Now I'm going to share with you an undocumented approach in handling popups. Speaking of ChromeWebBrowser control, it is very much of help that we know how it creates the webbrowser which, in reality, it doesn't. The control just hosts the webbrowser window handle. It has a private field called managedCefBrowserAdapter (ManagedCefBrowserAdapter class) that handles the actual creation of the web browser. ChromiumWEbBrowser implements the IWebBrowserInternal that has a method OnAfterBrowserCreated with a single parameter of type IBrowser. The control then invokes browser.GetHost().GetWindowHandle() to get the actual window handle (HWND) of the webbrowser it is being hosted. It is quite good.
The problem of the ChromeWebBrowser is that it won't have a constructor that accepts an IBrowser as an argument. It only has constructor that accepts HtmlString, string and IRequestContext arguments. These control waits for the
invocation of OnHandleCreated (a base class override) where it calls the managedCefBrowserAdapter.CreateBrowser after which it waits till its implementation of IWebBrowserInternal's OnAfterBrowserCreated is invoked.
Again, what is the approach that works?
Now, this approach that actually works is a product of long series of trial and error. One caution though is that I don't know why and how it works but I know it works.
First, I did not use ChromeWebBrowser. But I copied its code omitting the part where it creates .net control. In this case, I am targeting the browser's window handle (HWND) to be host by any object that exposes a HWND. Obviously I created a class (NativeCefWebBrowser) that uses the modified code. The ChromeWebBrowser orignal constructors were still there untouched becuase they are used to the create the parent webrowser. But I added one constructor that accept the following arguments: ICefBrowserParent parent (an interface I've created and IBrowser browser that receives the browser argument in the ILifeSpanHandler's OnBeforePopup. I also added a public method AttachBrowser that has a single parameter IBrowser that recieves the IBrowser argument in the ILifeSpanHandler's OnAfterCreated. It the browser that will be kept by CefNativeWebBrowser class.
Why didn't I keep the browser instance received form ILifeSpanHandler.OnBeforePopup but used the instance received from ILifeSpanHandler.OnAfterCreated when they are the same browser instance? This is one of those parts that I don't know why. One thing I noticed is that when I called browser.GetHost().GetWindowHandle() during ILiffeSpanHandler.OnBeforePopup, the first window handle I received was the different compared to when I invoked the method during ILifeSpanHandler.OnAfterCreatd. Because of that, I store the browser instance from the latter that I passed to the NativeCefWebBrowser.AttachBrowser for its safekeeping.
In the NativeCefWebBrowser(ICefBrowserParent parent, IBrowser browser) contructor, I set the private following fields to true: browsercreated, browserinitialized (chromewebbrwoser orginal fields) and isAttachingBrowser (added private field). You don't call the ManagedCefBrowserAdapter's CreateBrowser in this contructor in instead call its OnAfterBrowserCreated passing the browser instance. You don't much in this constructor as you will wait the ILifeSpanHandler implementor to pass you the browser instance it will receive during its OnAfterCreated method. Take note that when calling the ManagedCefBrowserAdapter's OnAfterBrowserCreated method, ManagedCefBrowserAdapter will still invoke IWebBrowserInternal implementation of OnAfterBrowserCreated that when happens you have to exit immediately when isAttachingBrowser is true as the following code will no sense no more.
After calling the NativeCefWebBrowser(ICefBrowserParent, IBroser) construct, you can normally set event listeners as you will normally do.
And that's it.
The following are parts of the code that I wrote
The ICefBrowserParent interface
public interface ICefBrowserParent
{
IntPtr Handle { get; }
Size ClientSize { get; }
bool Disposing { get; }
bool IsDisposed { get; }
bool InvokeRequired { get; }
IAsyncResult BeginInvoke(Delegate d);
object Invoke(Delegate d);
event EventHandler Resize;
}
As you would notice, the methods, properties and events in this interface are already implemented by the System.Windowns.Forms.Control class. So if you implementing this from class inhering Control class, you would not need to implement this anymore. This interface is only for non-Control class.
class NativeCefWebBrowser
{
public NativeCefWebBrowser(ICefBrowserParent, IBroser)
{
requestContext = browser.GetHost().RequestContext;
this.parent = parent; // added field
HasParent = true; // IWebBrowserInternal. I don't know what's this for
mustSetBounds = true; // added field
browserCreated = true;
isAttachingBrowser = true; // added field
InitializeFieldsAndCefIfRequired();
managedCefBrowserAdapter.OnAfterBrowserCreated(browser);
}
}
ILifeSpanHandler.OnBeforePopup(..., out IWebBrowser newWebBrowser)
{
CefNativeWebBrowser b = new CefNativeWebBrowser
(
parent, // defined else where
browser
);
// Attach event handlers
b.TitleChanged...;
newWebBrowser = b;
}
ILifeSpanHandler.OnAfterCreated(...)
{
((CefNativeWebBrowser)webBrowser).AttachBrowser(browser);
}