PanResponder

PanResponder is a higher level abstraction that can be used to recognize simple touch gestures. It gives you access to both the raw nativeEvent and a gestureState object.

The nativeEvent provides you all the touches and their locations. Whereas, gestureState is a wrapper object that also tracks accumulated distance, velocity and the touch origin (coordinates where the touch was when the responder was granted access).

Example

Run the example: rnplay.org/apps/Sxb2tQ

import React, { Component } from 'react';
import {
  AppRegistry,
  PanResponder,
  StyleSheet,
  View,
  processColor,
} from 'react-native';

var CIRCLE_SIZE = 80;


class PanResponderExample extends Component {

  constructor(props) {
      super(props);
    this._panResponder = {};
    this._previousLeft = 0;
    this._previousTop = 0;
    this._circleStyles = {};
    this.circle = null;
    }

  componentWillMount() {
    this._panResponder = PanResponder.create({
      onStartShouldSetPanResponder: this._handleStartShouldSetPanResponder,
      onMoveShouldSetPanResponder: this._handleMoveShouldSetPanResponder,
      onPanResponderGrant: this._handlePanResponderGrant,
      onPanResponderMove: this._handlePanResponderMove,
      onPanResponderRelease: this._handlePanResponderEnd,
      onPanResponderTerminate: this._handlePanResponderEnd,
    });
    this._previousLeft = 20;
    this._previousTop = 84;
    this._circleStyles = {
      style: {
        left: this._previousLeft,
        top: this._previousTop,
        backgroundColor: 'green',
      }
    };
  }

    componentDidMount() {
    this._updateNativeStyles();
  }

    render() {
    return (
      <View style={styles.container}>
        <View style={styles.circle}
          ref={(circle) => {
            this.circle = circle;
          }}
          { ...this._panResponder.panHandlers }
        />
      </View>
    );
  }

  _highlight = () => {
    this._circleStyles.style.backgroundColor = 'blue';
    this._updateNativeStyles();
  }

  _unHighlight = () => {
    this._circleStyles.style.backgroundColor = 'green';
    this._updateNativeStyles();
  }

  _updateNativeStyles() {
    this.circle && this.circle.setNativeProps(this._circleStyles);
  }

  _handleStartShouldSetPanResponder() {
    return true;
  }

  _handleMoveShouldSetPanResponder() {
    return true;
  }

  _handlePanResponderGrant = (e, gestureState) => {
    this._highlight();
  }

    _handlePanResponderMove = (e, gestureState) => {
    this._circleStyles.style.left = this._previousLeft + gestureState.dx;
    this._circleStyles.style.top = this._previousTop + gestureState.dy;
    this._updateNativeStyles();
  }

  _handlePanResponderEnd = (e, gestureState) => {
    this._unHighlight();
    this._previousLeft += gestureState.dx;
    this._previousTop += gestureState.dy;
  }

}

var styles = StyleSheet.create({
  circle: {
    width: CIRCLE_SIZE,
    height: CIRCLE_SIZE,
    borderRadius: CIRCLE_SIZE / 2,
    position: 'absolute',
    left: 0,
    top: 0,
  },
  container: {
    flex: 1,
    paddingTop: 64,
  },
});