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- /*
- * Copyright (c) 2019 - 2020 Arnaud Vergnet.
- *
- * This file is part of Campus INSAT.
- *
- * Campus INSAT is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Campus INSAT is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Campus INSAT. If not, see <https://www.gnu.org/licenses/>.
- */
-
- import {NativeScrollEvent, NativeSyntheticEvent} from 'react-native';
-
- const speedOffset = 5;
-
- type ListenerFunctionType = (shouldHide: boolean) => void;
-
- /**
- * Class used to detect when to show or hide a component based on scrolling
- */
- export default class AutoHideHandler {
- lastOffset: number;
-
- isHidden: boolean;
-
- listeners: Array<ListenerFunctionType>;
-
- constructor(startHidden: boolean) {
- this.listeners = [];
- this.isHidden = startHidden;
- this.lastOffset = 0;
- }
-
- /**
- * Adds a listener to the hide event
- *
- * @param listener
- */
- addListener(listener: (shouldHide: boolean) => void) {
- this.listeners.push(listener);
- }
-
- /**
- * Notifies every listener whether they should hide or show.
- *
- * @param shouldHide
- */
- notifyListeners(shouldHide: boolean) {
- this.listeners.forEach((func: ListenerFunctionType) => {
- func(shouldHide);
- });
- }
-
- /**
- * Callback to be used on the onScroll animated component event.
- *
- * Detects if the current speed exceeds a threshold and notifies listeners to hide or show.
- *
- * The hide even is triggered when the user scrolls down, and the show event on scroll up.
- * This does not take into account the speed when the y coordinate is negative, to prevent hiding on over scroll.
- * (When scrolling up and hitting the top on ios for example)
- *
- * //TODO Known issue:
- * When refreshing a list with the pull down gesture on ios,
- * this can trigger the hide event as it scrolls down the list to show the refresh indicator.
- * Android shows the refresh indicator on top of the list so this is not an issue.
- *
- * @param event The scroll event generated by the animated component onScroll prop
- */
- onScroll(event: NativeSyntheticEvent<NativeScrollEvent>) {
- const {nativeEvent} = event;
- const speed =
- nativeEvent.contentOffset.y < 0
- ? 0
- : this.lastOffset - nativeEvent.contentOffset.y;
- if (speed < -speedOffset && !this.isHidden) {
- // Go down
- this.notifyListeners(true);
- this.isHidden = true;
- } else if (speed > speedOffset && this.isHidden) {
- // Go up
- this.notifyListeners(false);
- this.isHidden = false;
- }
- this.lastOffset = nativeEvent.contentOffset.y;
- }
- }
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