React-Native : onPanResponderGrant Vs onPanResponderStart

Question

PanResponder.create() has many callbacks and two of them are onPanResponderGrant and onPanResponderStart. Both callbacks getting triggered as soon as screen is touched.react-native official documentation doesn't have much information about these callbacks.

Can anybody let me know the difference between these two callbacks and when to use which one?

Answer 1

onPanResponderGrant is called when a gesture is "started" while onPanResponderStart is called on additional gesture events.

For example, if you were to place one finger on the screen, onPanResponderGrant would fire, then, if a second finger is placed without removing the first onPanResponderStart would fire.

You can view some logic regarding this in the RN repo: https://github.com/facebook/react-native/blob/master/Libraries/Interaction/PanResponder.js