forked from vergnet/application-amicale
70 lines
2.1 KiB
JavaScript
70 lines
2.1 KiB
JavaScript
// @flow
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import * as React from 'react';
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const speedOffset = 5;
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/**
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* Class used to detect when to show or hide a component based on scrolling
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*/
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export default class AutoHideHandler {
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lastOffset: number;
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isHidden: boolean;
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listeners: Array<Function>;
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constructor(startHidden: boolean) {
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this.listeners = [];
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this.isHidden = startHidden;
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}
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/**
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* Adds a listener to the hide event
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*
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* @param listener
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*/
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addListener(listener: Function) {
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this.listeners.push(listener);
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}
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/**
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* Notifies every listener whether they should hide or show.
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*
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* @param shouldHide
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*/
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notifyListeners(shouldHide: boolean) {
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for (let i = 0; i < this.listeners.length; i++) {
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this.listeners[i](shouldHide);
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}
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}
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/**
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* Callback to be used on the onScroll animated component event.
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*
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* Detects if the current speed exceeds a threshold and notifies listeners to hide or show.
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*
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* The hide even is triggered when the user scrolls down, and the show event on scroll up.
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* This does not take into account the speed when the y coordinate is negative, to prevent hiding on over scroll.
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* (When scrolling up and hitting the top on ios for example)
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*
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* //TODO Known issue:
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* When refreshing a list with the pull down gesture on ios,
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* this can trigger the hide event as it scrolls down the list to show the refresh indicator.
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* Android shows the refresh indicator on top of the list so this is not an issue.
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*
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* @param nativeEvent The scroll event generated by the animated component onScroll prop
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*/
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onScroll({nativeEvent}: Object) {
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const speed = nativeEvent.contentOffset.y < 0 ? 0 : this.lastOffset - nativeEvent.contentOffset.y;
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if (speed < -speedOffset && !this.isHidden) { // Go down
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this.notifyListeners(true);
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this.isHidden = true;
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} else if (speed > speedOffset && this.isHidden) { // Go up
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this.notifyListeners(false);
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this.isHidden = false;
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}
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this.lastOffset = nativeEvent.contentOffset.y;
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}
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}
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