95 lines
3 KiB
TypeScript
95 lines
3 KiB
TypeScript
/*
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* Copyright (c) 2019 - 2020 Arnaud Vergnet.
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*
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* This file is part of Campus INSAT.
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*
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* Campus INSAT is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Campus INSAT is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Campus INSAT. If not, see <https://www.gnu.org/licenses/>.
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*/
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import { NativeScrollEvent, NativeSyntheticEvent } from 'react-native';
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const speedOffset = 5;
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type ListenerFunctionType = (shouldHide: boolean) => void;
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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<ListenerFunctionType>;
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constructor(startHidden: boolean) {
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this.listeners = [];
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this.isHidden = startHidden;
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this.lastOffset = 0;
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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: (shouldHide: boolean) => void) {
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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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this.listeners.forEach((func: ListenerFunctionType) => {
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func(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 event The scroll event generated by the animated component onScroll prop
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*/
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onScroll(event: NativeSyntheticEvent<NativeScrollEvent>) {
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const { nativeEvent } = event;
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const speed =
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nativeEvent.contentOffset.y < 0
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? 0
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: this.lastOffset - nativeEvent.contentOffset.y;
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if (speed < -speedOffset && !this.isHidden) {
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// 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) {
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// 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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