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joplin/ReactNativeClient/lib/components/ItemList.js

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JavaScript
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const React = require('react');
const { Text, TouchableHighlight, View, StyleSheet, ScrollView } = require('react-native');
class ItemList extends React.Component {
constructor() {
super();
this.scrollTop_ = 0;
}
itemCount(props = null) {
if (props === null) props = this.props;
return this.props.items ? this.props.items.length : this.props.itemComponents.length;
}
updateStateItemIndexes(props = null, height = null) {
if (props === null) props = this.props;
if (height === null) {
if (!this.state) return;
height = this.state.height;
}
const topItemIndex = Math.max(0, Math.floor(this.scrollTop_ / props.itemHeight));
const visibleItemCount = Math.ceil(height / props.itemHeight);
let bottomItemIndex = topItemIndex + visibleItemCount - 1;
if (bottomItemIndex >= this.itemCount(props)) bottomItemIndex = this.itemCount(props) - 1;
this.setState({
topItemIndex: topItemIndex,
bottomItemIndex: bottomItemIndex,
});
}
UNSAFE_componentWillMount() {
this.setState({
topItemIndex: 0,
bottomItemIndex: 0,
height: 0,
itemHeight: this.props.itemHeight ? this.props.itemHeight : 0,
});
this.updateStateItemIndexes();
}
UNSAFE_componentWillReceiveProps(newProps) {
if (newProps.itemHeight) {
this.setState({
itemHeight: newProps.itemHeight,
});
}
this.updateStateItemIndexes(newProps);
}
onScroll(event) {
this.scrollTop_ = Math.floor(event.nativeEvent.contentOffset.y);
this.updateStateItemIndexes();
}
onLayout(event) {
this.setState({ height: event.nativeEvent.layout.height });
this.updateStateItemIndexes(null, event.nativeEvent.layout.height);
}
render() {
const style = this.props.style ? this.props.style : {};
const itemHeight = this.state.itemHeight;
//if (!this.props.itemHeight) throw new Error('itemHeight is required');
let itemComps = [];
if (this.props.items) {
const items = this.props.items;
const blankItem = function(key, height) {
return <View key={key} style={{height:height}}></View>
}
itemComps = [blankItem('top', this.state.topItemIndex * this.props.itemHeight)];
for (let i = this.state.topItemIndex; i <= this.state.bottomItemIndex; i++) {
const itemComp = this.props.itemRenderer(items[i]);
itemComps.push(itemComp);
}
itemComps.push(blankItem('bottom', (items.length - this.state.bottomItemIndex - 1) * this.props.itemHeight));
} else {
itemComps = this.props.itemComponents;
}
return (
<ScrollView scrollEventThrottle={500} onLayout={(event) => { this.onLayout(event); }} style={style} onScroll={ (event) => { this.onScroll(event) }}>
{ itemComps }
</ScrollView>
);
}
}
module.exports = { ItemList };