/*
* 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 .
*/
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;
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) {
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;
}
}