MouseEnter and MouseLeave events of ChromiumWebBrowser control do not fire

[sarus]

Hello,

Not sure if I should be expecting this to work but the MouseLeave and MouseEnter events don't seem to work when using the ChromiumWebBrowser control for WinForms. Here's the code I was using. Should I be expecting these events to trigger properly on the browser control? Thank you!

        public WebView()
        {
            InitializeComponent();
            browser = new ChromiumWebBrowser("resource://web/index.html")
            {
                Dock = DockStyle.Fill,
            };

            mainPanel.Controls.Add(browser);

            browser.MouseLeave += new System.EventHandler(this.browser_MouseLeave);
            browser.MouseEnter += new System.EventHandler(this.browser_MouseEnter);           
        }

        void browser_MouseLeave(object sender, EventArgs e)
        {
            // Never Fires
            Console.WriteLine("Browser Mouse ENter");              
        }

        void browser_MouseEnter(object sender, EventArgs e)
        {
            // Never Fires
            Console.WriteLine("Browser Mouse Enter");
        }

I'm using the latest CefSharp available from Nuget (41.0.0)

[jankurianski]

The underlying CEF library captures all mouse events and does not bubble them up to WinForms. There's no way around this for WinForms - if you want to handle mouse events you need to do so in JavaScript.

Your alternative is to use the WPF CefSharp control, as this uses the underlying CEF library's OSR (Off Screen Rendering) mode, in which WPF is in charge of all keyboard and mouse events, and it passes them onto CEF. This would give you an opportunity to intercept whatever events you wanted.

[sarus]

Ah interesting thank you very much. Is the general recommendation to use the WPF control? We're "porting" an existing application that is built on winforms which is why I started with the winforms control but it is possible for us to move to WPF if needed (although a bit painful).

[amaitland]

You may be able to hook the underlying handle and capture the raw messages, e.g. WM_MOUSELEAVE using a NativeWindow implementation. Might be worth loading Spy++ and seeing if there's a handle that receives the messages.

[sarus]

@amaitland Thank you for the tip. I did try out listening for WM_MOUSELEAVE and WM_MOUSEMOVE but they didn't work well if the mouse was moving fast over the control (missed messages basically). For my use case where I was changing the opacity of the form on mouse hover (in the CSS sense) this resulted in issues where the state would become mixed up (hover when it wasn't hovered or vice versa). I've resorted to using a timer which checks the mouse position to see if it's contained within the bounds of the form. Kind of makes me cringe but it works well haha.

[amaitland]

What handle did you hook? It would likely need to be one of the child handles of the browser control it's self (one of the underlying handles for the CEF instance). There used to be a handle called something like Chrome_RenderWidgetHostHWND, I'd start there....

Are you actually interested in Focus? For which there are notification events.

https://github.com/cefsharp/CefSharp/blob/master/CefSharp.WinForms/Internals/DefaultFocusHandler.cs

[sarus]

@amaitland I'm pretty sure we aren't looking for focus. The actual use case here is to change the opacity of the form when the user's mouse is hovered over it. (transparent when there is no mouse hover and opaque when there is a mouse hover).

(I'm using hover here in the css sense, not the winform sense)

I'll take a look at the handles for the browser control itself and report back. Thanks!

[jankurianski]

@sarus Not sure if it helps but inspired by you and @amaitland I decided to try intercepting the mouse events to fix another problem I had. This is how I look for the Chrome_RenderWidgetHostHWND: https://gist.github.com/jankurianski/2163d7928d3d6f839e47

Let me know if you have a cleaner approach than using EnumWindow. I found that the widget window was the 3rd direct child from the ChromiumWebBrowser.Handle, which would be shorter but I guess more likely to break between Chromium releases.

[amaitland]

Nice one @jankurianski! An excellent reference 👍

[sarus]

@jankurianski Yes agree with amaitland. This is fantastic. Thank you for posting this Gist. Will try to find time in the next week to test it out. Have you noticed missing mouse events when using this approach?

As a test I hooked into the mouse events for the form itself to listen for WM_MOUSELEAVE and WM_MOUSEMOVE. I noticed that if I moved the mouse over the form very quickly the events were not always fired.

There was also this stackoverflow post basically outlining the same problem and hence the timer based solution:

http://stackoverflow.com/questions/12552809/mousehover-and-mouseleave-events-controlling

[jankurianski]

@sarus Changing the ChromeWidgetMessageInterceptor to the following implementation resulted in lots of WM_MOUSEMOVE messages, and I always seemed to get a WM_MOUSELEAVE message, even when I was quickly swiping in and out of the browser:

        class ChromeWidgetMessageInterceptor : NativeWindow
        {
            public ChromeWidgetMessageInterceptor(IntPtr chromeWidgetHostHandle)
            {
                AssignHandle(chromeWidgetHostHandle);
            }

            const int WM_MOUSEMOVE = 0x0200;
            const int WM_MOUSELEAVE = 0x02A3;

            protected override void WndProc(ref Message m)
            {
                base.WndProc(ref m);

                switch (m.Msg) {
                    case WM_MOUSEMOVE:
                        Console.WriteLine("WM_MOUSEMOVE");
                        break;
                    case WM_MOUSELEAVE:
                        Console.WriteLine("WM_MOUSELEAVE");
                        break;
                }
            }
        }

[amaitland]

I've added this is faq-able? Anymore more before closing?

[rassilon]

I don't think so. Other than maybe adding a comment to one of the example projects pointing at the gist and this issue maybe?

[qwqcode]

@sarus Changing the ChromeWidgetMessageInterceptor to the following implementation resulted in lots of WM_MOUSEMOVE messages, and I always seemed to get a WM_MOUSELEAVE message, even when I was quickly swiping in and out of the browser:

        class ChromeWidgetMessageInterceptor : NativeWindow
        {
            public ChromeWidgetMessageInterceptor(IntPtr chromeWidgetHostHandle)
            {
                AssignHandle(chromeWidgetHostHandle);
            }

            const int WM_MOUSEMOVE = 0x0200;
            const int WM_MOUSELEAVE = 0x02A3;

            protected override void WndProc(ref Message m)
            {
                base.WndProc(ref m);

                switch (m.Msg) {
                    case WM_MOUSEMOVE:
                        Console.WriteLine("WM_MOUSEMOVE");
                        break;
                    case WM_MOUSELEAVE:
                        Console.WriteLine("WM_MOUSELEAVE");
                        break;
                }
            }
        }

But const int WM_LBUTTONUP = 0x0202; can't receive ��

[MarcusN88]

@sarus Changing the ChromeWidgetMessageInterceptor to the following implementation resulted in lots of WM_MOUSEMOVE messages, and I always seemed to get a WM_MOUSELEAVE message, even when I was quickly swiping in and out of the browser:

        class ChromeWidgetMessageInterceptor : NativeWindow
        {
            public ChromeWidgetMessageInterceptor(IntPtr chromeWidgetHostHandle)
            {
                AssignHandle(chromeWidgetHostHandle);
            }

            const int WM_MOUSEMOVE = 0x0200;
            const int WM_MOUSELEAVE = 0x02A3;

            protected override void WndProc(ref Message m)
            {
                base.WndProc(ref m);

                switch (m.Msg) {
                    case WM_MOUSEMOVE:
                        Console.WriteLine("WM_MOUSEMOVE");
                        break;
                    case WM_MOUSELEAVE:
                        Console.WriteLine("WM_MOUSELEAVE");
                        break;
                }
            }
        }

But const int WM_LBUTTONUP = 0x0202; can't receive ��

Having the same problem. Also not working for WM_NCLBUTTONUP = 0x00A2;. Is there any other classname i could use to grab a handle of and get the messages for mouse button up?