:CloseBrowser(false (0)) instead of allowing the window to close immediately (see the examples below). This gives CEF an opportunity to process the 'onbeforeunload' event and optionally cancel the close before do_close() is called.
When windowed rendering is enabled CEF will internally create a window or view to host the browser. In that case returning false (0) from do_close() will send the standard close notification to the browser's top-level owner window (e.g. WM_CLOSE on Windows, performClose: on OS X, "delete_event" on Linux or cef_window_delegate_t::can_close() callback from Views). If the browser's host window/view has already been destroyed (via view hierarchy tear-down, for example) then do_close() will not be called for that browser since is no longer possible to cancel the close.
When windowed rendering is disabled returning false (0) from do_close() will cause the browser object to be destroyed immediately.
If the browser's top-level owner window requires a non-standard close notification then send that notification from do_close() and return true (1).
The cef_life_span_handler_t::on_before_close() function will be called after do_close() (if do_close() is called) and immediately before the browser object is destroyed. The application should only exit after on_before_close() has been called for all existing browsers.
The below examples describe what should happen during window close when the browser is parented to an application-provided top-level window.
Example 1: Using cef_browser_host_t::try_close_browser(). This is recommended for clients using standard close handling and windows created on the browser process UI thread. 1. User clicks the window close button which sends a close notification to the application's top-level window. 2. Application's top-level window receives the close notification and calls TryCloseBrowser() (which internally calls CloseBrowser(false)). TryCloseBrowser() returns false so the client cancels the window close. 3. JavaScript 'onbeforeunload' handler executes and shows the close confirmation dialog (which can be overridden via CefJSDialogHandler::OnBeforeUnloadDialog()). 4. User approves the close. 5. JavaScript 'onunload' handler executes. 6. CEF sends a close notification to the application's top-level window (because DoClose() returned false by default). 7. Application's top-level window receives the close notification and calls TryCloseBrowser(). TryCloseBrowser() returns true so the client allows the window close. 8. Application's top-level window is destroyed. 9. Application's on_before_close() handler is called and the browser object is destroyed. 10. Application exits by calling cef_quit_message_loop() if no other browsers exist.
Example 2: Using cef_browser_host_t::CloseBrowser(false (0)) and implementing the do_close() callback. This is recommended for clients using non-standard close handling or windows that were not created on the browser process UI thread. 1. User clicks the window close button which sends a close notification to the application's top-level window. 2. Application's top-level window receives the close notification and: A. Calls CefBrowserHost::CloseBrowser(false). B. Cancels the window close. 3. JavaScript 'onbeforeunload' handler executes and shows the close confirmation dialog (which can be overridden via CefJSDialogHandler::OnBeforeUnloadDialog()). 4. User approves the close. 5. JavaScript 'onunload' handler executes. 6. Application's do_close() handler is called. Application will: A. Set a flag to indicate that the next close attempt will be allowed. B. Return false. 7. CEF sends an close notification to the application's top-level window. 8. Application's top-level window receives the close notification and allows the window to close based on the flag from #6B. 9. Application's top-level window is destroyed. 10. Application's on_before_close() handler is called and the browser object is destroyed. 11. Application exits by calling cef_quit_message_loop() if no other browsers exist.
Called when a browser has received a request to close. This may result directly from a call to cef_browser_host_t::*close_browser() or indirectly if the browser is parented to a top-level window created by CEF and the user attempts to close that window (by clicking the 'X', for example). The do_close() function will be called after the JavaScript 'onunload' event has been fired.
An application should handle top-level owner window close notifications by calling cef_browser_host_t::try_close_browser() or