panResponder 每次触摸都从开始位置开始

Question

Trying to make swiper with React Native PanResponder. When I click again to button after release button starts at begining position. I tried using setOffset in onPanResponderGrant but that makes button exceeds parent container when you scroll it. If sser scrolled 45% of the containers half width I'm animating button to that halfs end.

Here is a link for my code https://snack.expo.io/@sargnec/react-native-swiper

Answer 1

I think I made it work, with a few changes:

1. I kept

   onPanResponderGrant: () => {
   this.pan.setOffset({x: this.pan.x._value});
   },handlePanResponderMove This is important so that, when a user click a second time on your button and make gestureState.dx = 10, you do read 10px, not dx since initial position (after first click)

2. on handlePanResponderMove, I commented "// this.setState({ xPosition: gestureState.dx })" Your "xPosition" is useful to know where was your point in the beginning, so xPosition + dx move past the limit or not. If you update it on panResponderMove, if you make many very small dx steps, you will reach DRAG_TOP_LIMIT before the end

3. on onPanResponderRelease: (a) Here, I changed the xPosition, and (b) I do not make a test "gesture.dx > DRAG_TOP_LIMIT", but "xPosition + gesture.dx > DRAG_TOP_LIMIT"

4. (optional) Actually, your xPosition is not used (and not useful) for the render, so you should remove it from the state and just make this._xPosition

So, here is the code

pan = new Animated.ValueXY();                                                                        
handlePanResponderMove = (e, gestureState) => {                                                      
    const currentValue = this.state.xPosition + gestureState.dx                                      
    if (currentValue > DRAG_TOP_LIMIT) {                                                             
        this.pan.setValue({ x: DRAG_TOP_LIMIT })                                                     
    } else if (currentValue < DRAG_ALT_LIMIT) {                                                      
        this.pan.setValue({ x: DRAG_ALT_LIMIT })                                                     
    } else {                                                                                         
        this.pan.setValue({ x: gestureState.dx })                                                    
    }                                                                                                
};                                                                                                                                                                                                       
panResponder = PanResponder.create({                                                                 
    onMoveShouldSetPanResponder: () => true,                                                         
    onPanResponderGrant: () => {                                                                     
        this.pan.setOffset({x: this.pan.x._value});                                                  
    },                                                                                               
    onPanResponderMove: (e, gestureState) => this.handlePanResponderMove(e, gestureState),           
    onPanResponderRelease: (e, gestureState) => {                                                    
        this.pan.flattenOffset();                                                                    
        const currPosition = gestureState.dx + this.state.xPosition                                  
        if (currPosition >= DRAG_TOP_LIMIT * 0.45) {                                                 
            Animated.timing(this.pan.x, {                                                            
                toValue: DRAG_TOP_LIMIT,                                                             
                duration: 100                                                                        
            }).start()                                                                               
            this.setState({xPosition: DRAG_TOP_LIMIT})                                               
        } else if (currPosition <= DRAG_ALT_LIMIT * 0.45) {                                          
            Animated.timing(this.pan.x, {                                                            
                toValue: DRAG_ALT_LIMIT,                                                             
                duration: 100                                                                        
            }).start()                                                                               
            this.setState({xPosition: DRAG_ALT_LIMIT})                                               
        } else {                                                                                     
          this.setState({xPosition: this.state.xPosition + gestureState.dx })                        
        }                                                                                            
    }                                                                                                
})