onStartShouldSetPanResponder: (evt, gestureState) => evt. nativeEvent.touches.length is always equal to 1

[qiaolin-pan]

this._panResponder = PanResponder.create({
    ...
    onStartShouldSetPanResponder: (evt, gestureState) => {
        // When I use two fingers, it is also equal to 1
        console.log(evt.nativeEvent.touches.length);
    },
    ...
});

<View {...this._panResponder.panHandlers}>
    <PhotoView />
</View>

How can I resolve this ? Sorry, my English is not good