rn实现一个view的拖拽

// dx 和 dy：从触摸操作开始到现在的累积横向/纵向路程
//
// moveX 和 moveY：最近一次移动时的屏幕横/纵坐标
//
// numberActiveTouches：当前在屏幕上的有效触摸点的数量
//
// stated：和之前一样，用来识别手指的ID
//
// vx 和 vy：当前横向/纵向移动的速度
//
// x0 和 y0：当触摸操作开始时组件相对于屏幕的横/纵坐标

import React, {PureComponent, Component} from ‘react‘;
import {
    AppRegistry,
    StyleSheet,
    Text,
    View,
    PanResponder,
} from ‘react-native‘;

export default class TouchStartAndRelease extends PureComponent {
    constructor(props) {
        super(props);
        this.state = {
            backgroundColor: ‘red‘,
            marginTop: 100,
            marginLeft: 100,
        };
        this.lastX = this.state.marginLeft;
        this.lastY = this.state.marginTop;
    }

    componentWillMount(){
        this._panResponder = PanResponder.create({
            onStartShouldSetPanResponder: (evt, gestureState) => {
                return true;
            },
            onMoveShouldSetPanResponder:  (evt, gestureState) => {
                return true;
            },
            onPanResponderGrant: (evt, gestureState) => {
                this._highlight();
            },
            onPanResponderMove: (evt, gestureState) => {
                console.log(`gestureState.dx : ${gestureState.dx}   gestureState.dy : ${gestureState.dy}`);
                this.setState({
                    marginLeft: this.lastX + gestureState.dx,
                    marginTop: this.lastY + gestureState.dy,
                });
            },
            onPanResponderRelease: (evt, gestureState) => {
                this._unhighlight();
                this.lastX = this.state.marginLeft;
                this.lastY = this.state.marginTop;
            },
            onPanResponderTerminate: (evt, gestureState) => {
            },
        });
    }

    _unhighlight(){
        this.setState({
            backgroundColor: ‘red‘,
        });
    }

    _highlight(){
        this.setState({
            backgroundColor: ‘blue‘,
        });
    }

    render() {
        return (
            <View style={styles.container}>
                <View style={[styles.redView,
                    {
                        backgroundColor: this.state.backgroundColor,
                        marginTop: this.state.marginTop,
                        marginLeft: this.state.marginLeft,
                    }
                ]}
                      {...this._panResponder.panHandlers}
                />
            </View>
        );
    }
}

const styles = StyleSheet.create({
    container: {
        flex: 1,
    },
    redView: {
        width: 100,
        height: 100,
    },

});