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67 lines
2.9 KiB
Markdown
67 lines
2.9 KiB
Markdown
Timers are an important part of an application and React Native implements the [browser timers](https://developer.mozilla.org/en-US/Add-ons/Code_snippets/Timers).
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## Timers
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- setTimeout, clearTimeout
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- setInterval, clearInterval
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- setImmediate, clearImmediate
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- requestAnimationFrame, cancelAnimationFrame
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`requestAnimationFrame(fn)` is the exact equivalent of `setTimeout(fn, 0)`, they are triggered right after the screen has been flushed.
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`setImmediate` is executed at the end of the current JavaScript execution block, right before sending the batched response back to native. Note that if you call `setImmediate` within a `setImmediate` callback, it will be executed right away, it won't yield back to native in between.
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The `Promise` implementation uses `setImmediate` its asynchronicity primitive.
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## InteractionManager
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One reason why native apps feel so good performance wise is that barely any work is being done during an interaction/animation. In React Native, you can use `InteractionManager` that allows long-running work to be scheduled after any interactions/animations have completed.
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Applications can schedule tasks to run after interactions with the following:
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```javascript
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InteractionManager.runAfterInteractions(() => {
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// ...long-running synchronous task...
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});
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```
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Compare this to other scheduling alternatives:
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- requestAnimationFrame(): for code that animates a view over time.
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- setImmediate/setTimeout/setInterval(): run code later, note this may delay animations.
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- runAfterInteractions(): run code later, without delaying active animations.
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The touch handling system considers one or more active touches to be an 'interaction' and will delay `runAfterInteractions()` callbacks until all touches have ended or been cancelled.
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InteractionManager also allows applications to register animations by creating an interaction 'handle' on animation start, and clearing it upon completion:
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```javascript
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var handle = InteractionManager.createInteractionHandle();
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// run animation... (`runAfterInteractions` tasks are queued)
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// later, on animation completion:
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InteractionManager.clearInteractionHandle(handle);
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// queued tasks run if all handles were cleared
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```
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## TimerMixin
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We found out that the primary cause of fatals in apps created with React Native was due to timers firing after a component was unmounted. To solve this recurring issue, we introduced `TimerMixin`. If you include `TimerMixin`, then you can replace your calls to `setTimeout(fn, 500)` with `this.setTimeout(fn, 500)` (just prepend `this.`) and everything will be properly cleaned up for you when the component unmounts.
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```javascript
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var { TimerMixin } = React;
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var Component = React.createClass({
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mixins: [TimerMixin],
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componentDidMount: function() {
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this.setTimeout(
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() => { console.log('I do not leak!'); },
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500
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);
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}
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});
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```
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We highly recommend never using bare timers and always using this mixin, it will save you from a lot of hard to track down bugs.
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