RikuloRikulo

Handle DOM Events

To interact with the user, you can listen to the DOM events you care and response accordingly. To do so, you can register a DOM event listener.

Depending on your requirement, you can register it anytime you prefer. For example, you can defer the registration until it is really required.

If you have to handle it for every instance, you can register it in View.render_() after instantiating the DOM element. For example,

void render_() {
  final node = new Element.html('<div><div class="foo-button"></div></div>');
  node.query("div.foo-button").on.add((event) {
    //handle it
    });
  return node;
}

The Default Handling of DOM Events

View handles all DOM events automatically, such as click, focus, blur, mouseOver and etc. The default handling is so-called event proxy. As its name suggests, it proxies a DOM event with an instance of DomEvent (a subclass of ViewEvent). Then, send the instance to the view, if the user ever registers an event (by using View.on).

In other words, you don't have to handle DOM events, if you just want to proxy them with ViewEvent. For example, the following snippet works well without any assistant code.

view.on.click.add((e) {
  //do something
  });

TestDragAndDrop.dart is an example that handles the drag and drop events transparently. All these events are handled by the default event proxy.

View.onEventListened_()

The event proxy is actually handled by View.onEventListened_(). You can override if you'd like to intercept the default handling. For example,

void onEventListened_(String type, [Element target]) {
  if (type == "change") {
    //handle it specially
  } else {
    super.onEventListened_(type, target);
  }
}

If the DOM event is an input event, such as change and keyDown, the default implementation will check if a child element is INPUT, TEXTAREA, SELECT, BUTTON, and A. Then, pass it to the target argument. Otherwise, View.node is passed.

If it is not what you want, you can override it to specify the right element:

void onEventListened_(String type, [Element target]) {
  super.onEventListened_(type, type == "change" ? getNode("inp"): target);
}