react-native/Examples/UIExplorer/PanResponderExample.js

/**
 * The examples provided by Facebook are for non-commercial testing and
 * evaluation purposes only.
 *
 * Facebook reserves all rights not expressly granted.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL
 * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * @flow-weak
 */
'use strict';

var React = require('react-native');
var {
  PanResponder,
  StyleSheet,
  View,
  processColor,
} = React;

var CIRCLE_SIZE = 80;
var CIRCLE_COLOR = 'blue';
var CIRCLE_HIGHLIGHT_COLOR = 'green';

var PanResponderExample = React.createClass({

  statics: {
    title: 'PanResponder Sample',
    description: 'Shows the use of PanResponder to provide basic gesture handling.',
  },

  _panResponder: {},
  _previousLeft: 0,
  _previousTop: 0,
  _circleStyles: {},
  circle: (null : ?{ setNativeProps(props: Object): void }),

  componentWillMount: function() {
    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
      }
    };
  },

  componentDidMount: function() {
    this._updatePosition();
  },

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

  _highlight: function() {
    this.circle && this.circle.setNativeProps({
      style: {
        backgroundColor: processColor(CIRCLE_HIGHLIGHT_COLOR)
      }
    });
  },

  _unHighlight: function() {
    this.circle && this.circle.setNativeProps({
      style: {
        backgroundColor: processColor(CIRCLE_COLOR)
      }
    });
  },

  _updatePosition: function() {
    this.circle && this.circle.setNativeProps(this._circleStyles);
  },

  _handleStartShouldSetPanResponder: function(e: Object, gestureState: Object): boolean {
    // Should we become active when the user presses down on the circle?
    return true;
  },

  _handleMoveShouldSetPanResponder: function(e: Object, gestureState: Object): boolean {
    // Should we become active when the user moves a touch over the circle?
    return true;
  },

  _handlePanResponderGrant: function(e: Object, gestureState: Object) {
    this._highlight();
  },
  _handlePanResponderMove: function(e: Object, gestureState: Object) {
    this._circleStyles.style.left = this._previousLeft + gestureState.dx;
    this._circleStyles.style.top = this._previousTop + gestureState.dy;
    this._updatePosition();
  },
  _handlePanResponderEnd: function(e: Object, gestureState: Object) {
    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,
    backgroundColor: CIRCLE_COLOR,
    position: 'absolute',
    left: 0,
    top: 0,
  },
  container: {
    flex: 1,
    paddingTop: 64,
  },
});

module.exports = PanResponderExample;