For a detailed view of all the animation functions that angular provide I would recommand this great article of Year Of Moo. In this article we’ll focus on some limits and how to workaround.
Let’s build a simple fading animation on a list of movies :
In this case the animation will apply only on the
ul element. Here is how you can apply this animation on each element with delay between each
li (stagger) :
Ok, it looks cool. But as a developer I want to be able to reuse my animations. For that I’ll create an AnimationReferenceMetadata and use it for this transition:
Great ! But, now I need to customize the properties of my animation depending on the component I’m on. No problem :
Ok, ok, but I don’t always want to apply this animation on
li elements. Why not use a params for that ?
Unfortunately, Angular Animation doesn’t support params for
stagger value :
Ok, not a big deal. Let’s use a function to create our animation :
This work in dev mode, but it will produce an error at compile time in production mode : “Function expressions are not supported in decorators in ‘fade’”
Here we see that the only parameters we can change are in the
style or in
animate. And even here, it works only with pre-compiled values. We cannot change parameters based on the element current position for example.
To workaround these limitations, Angular Animtation provides an
AnimationBuilder service that can build animation players at runtime.
Here we create a ViewChild to reference our movie list. And on init, we create a player that run the animation once. We use the previous animation function in
buildand add the params in
Looks cool, but we have a problem of interroperability between the two methods (compiletime and runtime). Let’s refactor the animation:
Let’s update a little bit our template, to see the two methods in action side-by-side :
Here we animate the list of
lion init with the Animation Player, and when we click on “Add” this will trigger the
:entertransition of the new
Animation Player is powerful, but it doesn’t manage state transitions. Here we leverage the components hooks
ngOnInit to mimic
:enter. We could also have used
:leave, but for more complexe state management we’ll need to implement it ourself.
Now that we have the foundations, we can create a library of reusable animations for Angular. And improve the Animation Player experience by wrapping it up inside a directive.