How to add CSS AnimationEnd event handler to GWT widget?

Question

I would like my GWT widget to be notified when its CSS animation is over.

In plain HTML/Javascript this is easily done by registering an event handler like so:

elem.addEventListener("webkitAnimationEnd", function(){
    // do something
}, false);
// add more for Mozilla etc.

How can I do this in GWT?

This type of event is unknown to GWT's DOMImpl classes, so I keep getting an error "Trying to sink unknown event type webkitAnimationEnd".

Thanks!

Answer 1

You can always write some of the native (JavaScript) code yourself:

public class CssAnimation {
  public static native void registerCssCallback(
      Element elem, AsyncCallback<Void> callback) /*-{
    elem.addEventListener("webkitAnimationEnd", function() {
      $entry(@CssAnimation::cssCallback(Lcom/google/gwt/user/client/rpc/AsyncCallback;)(callback));
    }, false);
  }-*/;


  protected static void cssCallback(AsyncCallback<Void> callback) {
    callback.onSuccess(null);
  }
}

I haven't tried the code above. Let me know if it works as expected.

---

You can use GWT's Animation class to achieve the same effect. For example,

  new com.google.gwt.animation.client.Animation() {
    final com.google.gwt.dom.client.Style es = widget.getElement().getStyle();

    @Override
    protected void onUpdate(double progress) {
      setOpacity(1 - interpolate(progress));
    }

    private void setOpacity(double opacity) {
      es.setProperty("opacity", Double.toString(opacity));
      es.setProperty("filter", "alpha(opacity=" + 100 * opacity + ")");
    }

    @Override
    protected void onComplete() {
      /* ... run some code when animation completes ... */
    }
  }.run(2000, 5000);

Answer 2

Based on Darthenius' answer and Clay Lenhart's Blog, I finally settled for this solution:

private native void registerAnimationEndHandler(final Element pElement,
    final CbAnimationEndHandlerIF pHandler)
/*-{
    var callback = function(){
       pHandler.@fully.qualified.CbAnimationEndHandlerIF::onAnimationEnd()();
    }
    if (navigator.userAgent.indexOf('MSIE') < 0) {  // no MSIE support
       pElement.addEventListener("webkitAnimationEnd", callback, false); // Webkit
       pElement.addEventListener("animationend", callback, false); // Mozilla
    }
}-*/;

The CbAnimationEndHandlerIF is a simple custom EventHandler interface:

public interface CbAnimationEndHandlerIF extends EventHandler
{
    void onAnimationEnd();
}

Works like a charm! Thanks Darthenius!

If anyone can spot a weakness in this, of course I'd be happy to know.

Answer 3

I expanded a bit on the solution from Darthenius. This code also includes a mechanism to remove the event handler when it is finished. This is what I needed for my application but may not be what you want in all contexts. YMMV!

My final code looks like this:

import com.google.gwt.dom.client.Element;
import com.google.gwt.user.client.rpc.AsyncCallback;

public class CssAnimation {
    public static native void registerCssCallback(Element elem, AsyncCallback<Void> callback) /*-{
        var eventListener = function () {
            $entry(@CssAnimation::cssCallback(Lcom/google/gwt/user/client/rpc/AsyncCallback;)(callback));
            elem.removeEventListener("webkitAnimationEnd", eventListener);
        };

        elem.addEventListener("webkitAnimationEnd", eventListener, false);
    }-*/;

    protected static void cssCallback(AsyncCallback<Void> callback) {
        callback.onSuccess(null);
    }
}