add_navigate_listener

[dandeto]

This is my first stab at creating several cross-platform event listeners! I do not have a Mac, so this only works on Linux GTK and Windows webview2. Hopefully this will inspire someone to port it to Mac.

The add_navigate_listener is a dead-simple function. When a new webpage has loaded, this listener calls whatever handler the user specified and passes it the current url. Here is an example:

void navigate_callback(const char* url) {
  std::cout << url << '\n';
  // any additional logic with the url here.
  // maybe if url is not https, navigate away.
}
...
// now pass the callback to the webview listener
w.add_navigate_listener(navigate_callback);

Feedback appreciated!

[justjosias]

Is generic event listener code possible? I don't think we want to add individual event listeners for every possible event.

[dandeto]

That progress is being tracked over at #659. I think it is possible for mac and linux, but it looks very difficult for windows, especially with our current architecture. I was going to just add this navigate listener and a window destroy listener so that the app can show a confirm dialogue and cancel the window close if the user changes his mind. dandeto@e4ef6e3
I haven't felt strongly about other listeners being necessary yet, but if I do I'll make a new PR, of course!

I still think we should ideally add a completely generic way to create any listener. If that is not possible, we should expose the platform specific event system. I'm still working on it.

Bottom-line, a navigate event listener is 100% necessary for a webview library, whether or not we create a more robust event system.

[justjosias]

Looking over this again, I agree that it should be added. But it needs to support macOS first. Help porting it would be much appreciated.