enable dragging of element in a ScrollView after long press

Question

I have implemented drag n drop list with panResponder and ScrollView. I want to be able to scroll the list even when I touch the item. Problem is that the item moves when I do the gesture to scroll. Of course I also want to be able to move the item but now it has the same gesture as scroll. I want to overcome it by enabling dragging the element only after it was long pressed (1,5 sec). How to implement it? I thought to use Touchable as an element with onPressIn / onPressOut just like described here: http://browniefed.com/blog/react-native-press-and-hold-button-actions/ and somehow to enable panResponder after the time period, but I don't know how to enable it programmatically.

Right now this is my code for element in the list:

class AccountItem extends Component {

  constructor(props) {
    super(props);
    this.state = {
      pan: new Animated.ValueXY(),
      zIndex: 0,
    }

    this.panResponder = PanResponder.create({
      onStartShouldSetPanResponder: () => true,
      onPanResponderGrant: (e, gestureState) => {
        this.setState({ zIndex: 100 });
        this.props.disableScroll();
      },
      onPanResponderMove: Animated.event([null, {
        dx: this.state.pan.x,
        dy: this.state.pan.y,
      }]),
      onPanResponderRelease: (e, gesture) => {
        this.props.submitNewPositions();
        Animated.spring(
          this.state.pan,
          {toValue:{ x:0, y:0 }}
        ).start();
        this.setState({ zIndex: 0 });
        this.props.enableScroll();
      }
    })
  }

  meassureMyComponent = (event) => {
    const { setElementPosition } = this.props;
    let posY = event.nativeEvent.layout.y;
    setElementPosition(posY);
  }

  render() {
    const {name, index, onChangeText, onRemoveAccount} = this.props;

    return (
        <Animated.View
          style={[this.state.pan.getLayout(), styles.container, {zIndex: this.state.zIndex}]}
          {...this.panResponder.panHandlers}
          onLayout={this.meassureMyComponent}
        >

some other components...

        </Animated.View>
    )
  }
}

export default AccountItem;

Answer 1

You can do this using a ref value to store if dragging should be enabled, and this can be accessed within the PanResponder. Using a ref ensures that the value won't be stale w.r.t the PanResponder; that is, the reference to the ref will be fixed at the initialisation of the PanResponder, but the underlying .current value can change. (This is unlike a useState value, which would be stale past the initialisation of the PanResponder.)

e.g.

const dragEnabledRef = useRef(false);

const pan = useRef(
  PanResponder.create({
     onStartShouldSetPanResponder: () => dragEnabledRef.current,
     onStartShouldSetPanResponderCapture: () => dragEnabledRef.current,
     onMoveShouldSetPanResponder: () => dragEnabledRef.current,
     onMoveShouldSetPanResponderCapture: () => dragEnabledRef.current,
     ...
     onPanResponderRelease: () => {
        ...
        dragEnabledRef.current = false
     }
  })
).current

return (
   <Pressable onLongPress={() => {
      dragEnabledRef.current = true
   }}>
      {children}
   </Pressable>
);

Answer 2

I met the same issue with you. My solution is to define 2 different panResponder handler for onLongPress and normal behaviour.

  _onLongPressPanResponder(){
    return PanResponder.create({
      onPanResponderTerminationRequest: () => false,
      onStartShouldSetPanResponderCapture: () => true,
      onPanResponderMove: Animated.event([
        null, {dx: this.state.pan.x, dy: this.state.pan.y},
      ]),
      onPanResponderRelease: (e, {vx, vy}) => {
        this.state.pan.flattenOffset()
        Animated.spring(this.state.pan, {         //This will make the draggable card back to its original position
           toValue: 0
        }).start();
        this.setState({panResponder: undefined})   //Clear panResponder when user release on long press
      }
    })
  }

  _normalPanResponder(){
    return PanResponder.create({
      onPanResponderTerminationRequest: () => false,
      onStartShouldSetPanResponderCapture: () => true,
      onPanResponderGrant: (e, gestureState) => {
        this.state.pan.setOffset({x: this.state.pan.x._value, y: this.state.pan.y._value});
        this.state.pan.setValue({x: 0, y: 0})
        this.longPressTimer=setTimeout(this._onLongPress, 400)  // this is where you trigger the onlongpress panResponder handler
      },
      onPanResponderRelease: (e, {vx, vy}) => {
        if (!this.state.panResponder) {
            clearTimeout(this.longPressTimer);   // clean the timeout handler
        }
      }
    })
  }

Define your _onLongPress function:

  _onLongPress(){
    // you can add some animation effect here as wll
    this.setState({panResponder: this._onLongPressPanResponder()})
  }

Define your constructor:

  constructor(props){
    super(props)
    this.state = {
      pan: new Animated.ValueXY()
    };
    this._onLongPress = this._onLongPress.bind(this)
    this._onLongPressPanResponder = this._onLongPressPanResponder.bind(this)
    this._normalPanResponder = this._normalPanResponder.bind(this)
    this.longPressTimer = null
  }

Finally, before you render, you should switch to different panResponder handlers according to the state:

  let panHandlers = {}
    if(this.state.panResponder){
      panHandlers = this.state.panResponder.panHandlers
    }else{
      panHandlers = this._normalPanResponder().panHandlers
    }

Then attach the panHandlers to your view {...panHandlers} You can even change the css for different panHandlers to show different effect.

Answer 3

If your only issue is that ScrollView scrolls when moving item, then I'll suggest simply to disable scrolling of parent for movement period. Like:

//component with ScrollView:
...
constructor() {
   super()
   this.state = {scrolling: true}
   this.enableScroll = this.enableScroll.bind(this)
   this.disableScroll = this.disableScroll.bind(this)
}

// inject those methods into Drag&Drop item as props:
enableScroll() {
  this.setState({scrolling: true})
} 
disableScroll() {
  this.setState({scrolling: false})
} 

...
<ScrollView scrollEnabled={this.state.scrolling} ... />
...

//component with drag&drop item:
...
onPanResponderGrant() {
  ... 
  this.props.disableScroll() 
  ...
}
onPanResponderRelease() {
  this.props.enableScroll() 
}

Make sure to cover all cases of release gesture (like onPanResponderTerminate etc.)