react-native/docs/panresponder.md

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PanResponder reconciles several touches into a single gesture. It makes single-touch gestures resilient to extra touches, and can be used to recognize simple multi-touch gestures.

By default, PanResponder holds an InteractionManager handle to block long-running JS events from interrupting active gestures.

It provides a predictable wrapper of the responder handlers provided by the gesture responder system. For each handler, it provides a new gestureState object alongside the native event object:

onPanResponderMove: (event, gestureState) => {}

A native event is a synthetic touch event with the following form:

• nativeEvent
  • changedTouches - Array of all touch events that have changed since the last event
  • identifier - The ID of the touch
  • locationX - The X position of the touch, relative to the element
  • locationY - The Y position of the touch, relative to the element
  • pageX - The X position of the touch, relative to the root element
  • pageY - The Y position of the touch, relative to the root element
  • target - The node id of the element receiving the touch event
  • timestamp - A time identifier for the touch, useful for velocity calculation
  • touches - Array of all current touches on the screen

A gestureState object has the following:

• stateID - ID of the gestureState- persisted as long as there at least one touch on screen
• moveX - the latest screen coordinates of the recently-moved touch
• moveY - the latest screen coordinates of the recently-moved touch
• x0 - the screen coordinates of the responder grant
• y0 - the screen coordinates of the responder grant
• dx - accumulated distance of the gesture since the touch started
• dy - accumulated distance of the gesture since the touch started
• vx - current velocity of the gesture
• vy - current velocity of the gesture
• numberActiveTouches - Number of touches currently on screen

Basic Usage

  componentWillMount: function() {
    this._panResponder = PanResponder.create({
      // Ask to be the responder:
      onStartShouldSetPanResponder: (evt, gestureState) => true,
      onStartShouldSetPanResponderCapture: (evt, gestureState) => true,
      onMoveShouldSetPanResponder: (evt, gestureState) => true,
      onMoveShouldSetPanResponderCapture: (evt, gestureState) => true,

      onPanResponderGrant: (evt, gestureState) => {
        // The gesture has started. Show visual feedback so the user knows
        // what is happening!

        // gestureState.d{x,y} will be set to zero now
      },
      onPanResponderMove: (evt, gestureState) => {
        // The most recent move distance is gestureState.move{X,Y}

        // The accumulated gesture distance since becoming responder is
        // gestureState.d{x,y}
      },
      onPanResponderTerminationRequest: (evt, gestureState) => true,
      onPanResponderRelease: (evt, gestureState) => {
        // The user has released all touches while this view is the
        // responder. This typically means a gesture has succeeded
      },
      onPanResponderTerminate: (evt, gestureState) => {
        // Another component has become the responder, so this gesture
        // should be cancelled
      },
      onShouldBlockNativeResponder: (evt, gestureState) => {
        // Returns whether this component should block native components from becoming the JS
        // responder. Returns true by default. Is currently only supported on android.
        return true;
      },
    });
  },

  render: function() {
    return (
      <View {...this._panResponder.panHandlers} />
    );
  },

Working Example

To see it in action, try the PanResponder example in RNTester

Methods

• create

---

Reference

Methods

create()

PanResponder.create(config)

Enhanced versions of all of the responder callbacks that provide not only the typical ResponderSyntheticEvent, but also the PanResponder gesture state. Simply replace the word Responder with PanResponder in each of the typical onResponder* callbacks.

For example, the config object would look like:

• onMoveShouldSetPanResponder: (e, gestureState) => {...}
• onMoveShouldSetPanResponderCapture: (e, gestureState) => {...}
• onStartShouldSetPanResponder: (e, gestureState) => {...}
• onStartShouldSetPanResponderCapture: (e, gestureState) => {...}
• onPanResponderReject: (e, gestureState) => {...}
• onPanResponderGrant: (e, gestureState) => {...}
• onPanResponderStart: (e, gestureState) => {...}
• onPanResponderEnd: (e, gestureState) => {...}
• onPanResponderRelease: (e, gestureState) => {...}
• onPanResponderMove: (e, gestureState) => {...}
• onPanResponderTerminate: (e, gestureState) => {...}
• onPanResponderTerminationRequest: (e, gestureState) => {...}
• onShouldBlockNativeResponder: (e, gestureState) => {...}

In general, for events that have capture equivalents, we update the gestureState once in the capture phase and can use it in the bubble phase as well.

Be careful with onStartShould* callbacks. They only reflect updated gestureState for start/end events that bubble/capture to the Node. Once the node is the responder, you can rely on every start/end event being processed by the gesture and gestureState being updated accordingly. (numberActiveTouches) may not be totally accurate unless you are the responder.