370 lines
15 KiB
Markdown
370 lines
15 KiB
Markdown
@title
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Animations
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@intro
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A guide to Angular's animation system.
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@description
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Motion is an important aspect in the design of modern web applications. Good
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user interfaces transition smoothly between states with engaging animations
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that call attention where it's needed. Well-designed animations can make a UI not only
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more fun but also easier to use.
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Angular's animation system lets you build animations that run with the same kind of native
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performance found in pure CSS animations. You can also tightly integrate your
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animation logic with the rest of your application code, for ease of control.
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~~~ {.alert.is-helpful}
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Angular animations are built on top of the standard [Web Animations API](https://w3c.github.io/web-animations/)
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and run natively on [browsers that support it](http://caniuse.com/#feat=web-animation).
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For other browsers, a polyfill is required. Grab
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[`web-animations.min.js` from GitHub](https://github.com/web-animations/web-animations-js) and
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add it to your page.
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~~~
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# Contents
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* [Example: Transitioning between two states](#example-transitioning-between-states).
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* [States and transitions](#states-and-transitions).
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* [Example: Entering and leaving](#example-entering-and-leaving).
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* [Example: Entering and leaving from different states](#example-entering-and-leaving-from-different-states).
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* [Animatable properties and units](#animatable-properties-and-units).
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* [Automatic property calculation](#automatic-property-calculation).
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* [Animation timing](#animation-timing).
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* [Multi-step animations with keyframes](#multi-step-animations-with-keyframes).
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* [Parallel animation groups](#parallel-animation-groups).
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* [Animation callbacks](#animation-callbacks).
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The examples in this page are available as a <live-example></live-example>.
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{@a example-transitioning-between-states}
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## Quickstart example: Transitioning between two states
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<figure>
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<img src="/resources/images/devguide/animations/animation_basic_click.gif" alt="A simple transition animation" align="right" style="width:220px;margin-left:20px"> </img>
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</figure>
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You can build a simple animation that transitions an element between two states
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driven by a model attribute.
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Animations are defined inside `@Component` metadata. Before you can add animations, you need
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to import a few animation-specific functions:
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{@example 'animations/ts/src/app/hero-list-basic.component.ts' region='imports'}
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With these, you can define an *animation trigger* called `heroState` in the component
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metadata. It uses animations to transition between two states: `active` and `inactive`. When a
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hero is active, the element appears in a slightly larger size and lighter color.
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{@example 'animations/ts/src/app/hero-list-basic.component.ts' region='animationdef'}
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~~~ {.alert.is-helpful}
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In this example, you are defining animation styles (color and transform) inline in the
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animation metadata.
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~~~
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Now, using the `[@triggerName]` syntax, attach the animation that you just defined to
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one or more elements in the component's template.
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{@example 'animations/ts/src/app/hero-list-basic.component.ts' region='template'}
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Here, the animation trigger applies to every element repeated by an `ngFor`. Each of
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the repeated elements animates independently. The value of the
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attribute is bound to the expression `hero.state` and is always either `active` or `inactive`.
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With this setup, an animated transition appears whenever a hero object changes state.
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Here's the full component implementation:
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{@example 'animations/ts/src/app/hero-list-basic.component.ts'}
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## States and transitions
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Angular animations are defined as logical **states** and **transitions**
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between states.
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An animation state is a string value that you define in your application code. In the example
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above, the states `'active'` and `'inactive'` are based on the logical state of
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hero objects. The source of the state can be a simple object attribute, as it was in this case,
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or it can be a value computed in a method. The important thing is that you can read it into the
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component's template.
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You can define *styles* for each animation state:
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{@example 'animations/ts/src/app/hero-list-basic.component.ts' region='states'}
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These `state` definitions specify the *end styles* of each state.
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They are applied to the element once it has transitioned to that state, and stay
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*as long as it remains in that state*. In effect, you're defining what styles the element has in different states.
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After you define states, you can define *transitions* between the states. Each transition
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controls the timing of switching between one set of styles and the next:
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{@example 'animations/ts/src/app/hero-list-basic.component.ts' region='transitions'}
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<figure class='image-display'>
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<img src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active.png" alt="In Angular animations you define states and transitions between states" width="400"> </img>
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</figure>
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If several transitions have the same timing configuration, you can combine
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them into the same `transition` definition:
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{@example 'animations/ts/src/app/hero-list-combined-transitions.component.ts' region='transitions'}
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When both directions of a transition have the same timing, as in the previous
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example, you can use the shorthand syntax `<=>`:
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{@example 'animations/ts/src/app/hero-list-twoway.component.ts' region='transitions'}
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You can also apply a style during an animation but not keep it around
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after the animation finishes. You can define such styles inline, in the `transition`. In this example,
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the element receives one set of styles immediately and is then animated to the next.
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When the transition finishes, none of these styles are kept because they're not
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defined in a `state`.
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{@example 'animations/ts/src/app/hero-list-inline-styles.component.ts' region='transitions'}
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### The wildcard state `*`
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The `*` ("wildcard") state matches *any* animation state. This is useful for defining styles and
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transitions that apply regardless of which state the animation is in. For example:
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* The `active => *` transition applies when the element's state changes from `active` to anything else.
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* The `* => *` transition applies when *any* change between two states takes place.
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<figure class='image-display'>
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<img src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active_wildcards.png" alt="The wildcard state can be used to match many different transitions at once" width="400"> </img>
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</figure>
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### The `void` state
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The special state called `void` can apply to any animation. It applies
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when the element is *not* attached to a view, perhaps because it has not yet been
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added or because it has been removed. The `void` state is useful for defining enter and
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leave animations.
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For example the `* => void` transition applies when the element leaves the view,
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regardless of what state it was in before it left.
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<figure class='image-display'>
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<img src="/resources/images/devguide/animations/ng_animate_transitions_void_in.png" alt="The void state can be used for enter and leave transitions" width="400"> </img>
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</figure>
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The wildcard state `*` also matches `void`.
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## Example: Entering and leaving
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<figure>
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<img src="/resources/images/devguide/animations/animation_enter_leave.gif" alt="Enter and leave animations" align="right" style="width:250px;"> </img>
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</figure>
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Using the `void` and `*` states you can define transitions that animate the
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entering and leaving of elements:
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* Enter: `void => *`
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* Leave: `* => void`
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{@example 'animations/ts/src/app/hero-list-enter-leave.component.ts' region='animationdef'}
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Note that in this case the styles are applied to the void state directly in the
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transition definitions, and not in a separate `state(void)` definition. Thus, the transforms
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are different on enter and leave: the element enters from the left
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and leaves to the right.
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These two common animations have their own aliases:
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<code-example language="typescript">
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transition(':enter', [ ... ]); // void => *
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transition(':leave', [ ... ]); // * => void
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</code-example>
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## Example: Entering and leaving from different states
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<figure>
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<img src="/resources/images/devguide/animations/animation_enter_leave_states.gif" alt="Enter and leave animations combined with state animations" align="right" style="width:200px"> </img>
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</figure>
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You can also combine this animation with the earlier state transition animation by
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using the hero state as the animation state. This lets you configure
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different transitions for entering and leaving based on what the state of the hero
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is:
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* Inactive hero enter: `void => inactive`
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* Active hero enter: `void => active`
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* Inactive hero leave: `inactive => void`
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* Active hero leave: `active => void`
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This gives you fine-grained control over each transition:
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<figure class='image-display'>
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<img src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active_void.png" alt="This example transitions between active, inactive, and void states" width="400"> </img>
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</figure>
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{@example 'animations/ts/src/app/hero-list-enter-leave-states.component.ts' region='animationdef'}
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## Animatable properties and units
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Since Angular's animation support builds on top of Web Animations, you can animate any property
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that the browser considers *animatable*. This includes positions, sizes, transforms, colors,
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borders, and many others. The W3C maintains
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[a list of animatable properties](https://www.w3.org/TR/css3-transitions/#animatable-properties)
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on its [CSS Transitions page](https://www.w3.org/TR/css3-transitions).
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For positional properties that have a numeric value, you can define a unit by providing
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the value as a string with the appropriate suffix:
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* `'50px'`
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* `'3em'`
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* `'100%'`
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If you don't provide a unit when specifying dimension, Angular assumes the default of `px`:
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* `50` is the same as saying `'50px'`
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## Automatic property calculation
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<figure>
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<img src="/resources/images/devguide/animations/animation_auto.gif" alt="Animation with automated height calculation" align="right" style="width:220px;margin-left:20px"> </img>
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</figure>
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Sometimes you don't know the value of a dimensional style property until runtime.
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For example, elements often have widths and heights that
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depend on their content and the screen size. These properties are often tricky
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to animate with CSS.
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In these cases, you can use a special `*` property value so that the value of the
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property is computed at runtime and then plugged into the animation.
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In this example, the leave animation takes whatever height the element has before it
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leaves and animates from that height to zero:
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{@example 'animations/ts/src/app/hero-list-auto.component.ts' region='animationdef'}
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## Animation timing
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There are three timing properties you can tune for every animated transition:
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the duration, the delay, and the easing function. They are all combined into
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a single transition *timing string*.
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### Duration
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The duration controls how long the animation takes to run from start to finish.
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You can define a duration in three ways:
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* As a plain number, in milliseconds: `100`
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* In a string, as milliseconds: `'100ms'`
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* In a string, as seconds: `'0.1s'`
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### Delay
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The delay controls the length of time between the animation trigger and the beginning
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of the transition. You can define one by adding it to the same string
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following the duration. It also has the same format options as the duration:
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* Wait for 100ms and then run for 200ms: `'0.2s 100ms'`
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### Easing
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The [easing function](http://easings.net/) controls how the animation accelerates
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and decelerates during its runtime. For example, an `ease-in` function causes
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the animation to begin relatively slowly but pick up speed as it progresses. You
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can control the easing by adding it as a *third* value in the string after the duration
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and the delay (or as the *second* value when there is no delay):
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* Wait for 100ms and then run for 200ms, with easing: `'0.2s 100ms ease-out'`
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* Run for 200ms, with easing: `'0.2s ease-in-out'`
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<figure>
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<img src="/resources/images/devguide/animations/animation_timings.gif" alt="Animations with specific timings" align="right" style="width:220px;margin-left:20px"> </img>
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</figure>
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### Example
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Here are a couple of custom timings in action. Both enter and leave last for
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200 milliseconds but they have different easings. The leave begins after a
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slight delay:
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{@example 'animations/ts/src/app/hero-list-timings.component.ts' region='animationdef'}
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## Multi-step animations with keyframes
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<figure>
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<img src="/resources/images/devguide/animations/animation_multistep.gif" alt="Animations with some bounce implemented with keyframes" align="right" style="width:220px;margin-left:20px"> </img>
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</figure>
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Animation *keyframes* go beyond a simple transition to a more intricate animation
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that goes through one or more intermediate styles when transitioning between two sets of styles.
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For each keyframe, you specify an *offset* that defines at which point
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in the animation that keyframe applies. The offset is a number between zero,
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which marks the beginning of the animation, and one, which marks the end.
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This example adds some "bounce" to the enter and leave animations with
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keyframes:
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{@example 'animations/ts/src/app/hero-list-multistep.component.ts' region='animationdef'}
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Note that the offsets are *not* defined in terms of absolute time. They are relative
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measures from zero to one. The final timeline of the animation is based on the combination
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of keyframe offsets, duration, delay, and easing.
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Defining offsets for keyframes is optional. If you omit them, offsets with even
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spacing are automatically assigned. For example, three keyframes without predefined
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offsets receive offsets `0`, `0.5`, and `1`.
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## Parallel animation groups
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<figure>
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<img src="/resources/images/devguide/animations/animation_groups.gif" alt="Parallel animations with different timings, implemented with groups" align="right" style="width:220px;margin-left:20px"> </img>
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</figure>
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You've seen how to animate multiple style properties at the same time:
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just put all of them into the same `style()` definition.
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But you may also want to configure different *timings* for animations that happen
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in parallel. For example, you may want to animate two CSS properties but use a
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different easing function for each one.
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For this you can use animation *groups*. In this example, using groups both on
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enter and leave allows for two different timing configurations. Both
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are applied to the same element in parallel, but run independently of each other:
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{@example 'animations/ts/src/app/hero-list-groups.component.ts' region='animationdef'}
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One group animates the element transform and width; the other group animates the opacity.
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## Animation callbacks
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A callback is fired when an animation is started and also when it is done.
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In the keyframes example, you have a `trigger` called `@flyInOut`. There you can hook
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those callbacks like this:
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{@example 'animations/ts/src/app/hero-list-multistep.component.ts' region='template'}
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The callbacks receive an `AnimationTransitionEvent` which contains useful properties such as `fromState`,
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`toState` and `totalTime`.
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Those callbacks will fire whether or not an animation is picked up. |