Any reason why this._player.cancel() is called once animations finish in playAnimation function?

[JustinXinLiu]

I asked a question on SO a few days ago regarding maintaining the end state of a neon animation (http://stackoverflow.com/questions/31692377/how-to-maintain-the-end-state-of-a-neon-animation-in-polymer) and today I found this piece of code inside the function playAnimation in neon-animation-runner-behavior.html.

playAnimation: function(type, cookie) {
  var allConfigs = this.getAnimationConfig(type);
  if (!allConfigs) {
    return;
  }
  var allAnimations = this._configureAnimationEffects(allConfigs);
  var allEffects = allAnimations.map(function(animation) {
    return animation.effect;
  });

  if (allEffects.length > 0) {
    this._player = this._runAnimationEffects(allEffects);
    this._player.onfinish = function() {
      this._completeAnimations(allAnimations);

      if (this._player) {
        // not sure why this is needed?
        this._player.cancel();
        this._player = null;
      }

      this.fire('neon-animation-finish', cookie, {bubbles: false});
    }.bind(this);

  } else {
    this.fire('neon-animation-finish', cookie, {bubbles: false});
  }
},

I don't really understand why we need to cancel the animation upon the completion of it. Doing so will remove all effects from the source object and I have to manually set its final state once the animation finishes.

Can someone please shed some light on this?

[JustinXinLiu]

OK, now I see the side effects of having this line commented out.

So for me the fix is that to add a check around this._player.cancel(), when a type argument is passed in, meaning it's a custom animation, ignore the cancel.

      if (this._player) {
          if (!type) {
              this._player.cancel();
          }
        this._player = null;
      }

[ghost]

Just ran into this myself. I think there are many instances when you'd want to maintain the end state of the animation, at least until another event occurs, even for non-custom animations. Consider a login component, where you use a slide-up-animation to reveal the forgot password form. Right now, it would slide up to reveal the form, and then immediately slide back down out of view.

[kornalius]

+1