我对React-Native还是个新手,所以我很可能遗漏了一些核心概念。我想创建一个可拖动的元素,并能够将其移动回其原始位置。
第一部分没问题,但当我尝试更新位置时,它看起来像是在工作(因为当我再次单击时,元素将返回到其原始位置),但视图并未更新。
我尝试调用setState
和forceUpdate
,但没有更新视图。
你们知道为什么吗?
以下是我到目前为止所做的演示:
import React from 'react';
import {Button, StyleSheet, PanResponder, View, Animated} from 'react-native';
export default class Scene extends React.Component {
constructor(props) {
super(props)
const rectanglePosition = new Animated.ValueXY({ x: 0, y: 0 })
const rectanglePanResponder = this.createPanResponder();
this.state = {
rectanglePosition,
rectanglePanResponder
}
}
createPanResponder = () => {
return PanResponder.create({
onStartShouldSetPanResponder: () => true,
onPanResponderMove: (event, gesture) => {
this.state.rectanglePosition.setValue({ x: gesture.dx, y: gesture.dy });
},
onPanResponderRelease: () => {
this.state.rectanglePosition.flattenOffset();
},
onPanResponderGrant: () => {
this.state.rectanglePosition.setOffset({
x: this.state.rectanglePosition.x._value,
y: this.state.rectanglePosition.y._value
});
}
});
}
resetPosition = () => {
const newPosition = new Animated.ValueXY({ x: 0, y: 0 })
this.setState({ rectanglePosition: newPosition }) // I thought updating the state triggered a re-render
this.forceUpdate() // doesn't work either
}
getRectanglePositionStyles = () => {
return {
top: this.state.rectanglePosition.y._value,
left: this.state.rectanglePosition.x._value,
transform: this.state.rectanglePosition.getTranslateTransform()
}
}
render() {
return (
<View style={styles.container}>
<Animated.View
style={[styles.rectangle, this.getRectanglePositionStyles()]}
{...this.state.rectanglePanResponder.panHandlers}>
</Animated.View>
<View style={styles.footer}>
<Button title="Reset" onPress={this.resetPosition}></Button>
</View>
</View>
);
}
}
const styles = StyleSheet.create({
container: {
flex: 1,
borderColor: 'red',
backgroundColor: '#F5FCFF',
},
footer: {
borderWidth: 1,
width: '100%',
position: 'absolute',
bottom: 0,
left: 0,
backgroundColor: 'blue',
},
rectangle: {
position: 'absolute',
height: 50,
width: 50,
backgroundColor: 'red'
}
});
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