Inconsistent documentation: onShouldBlockNativeResponder works on iOS

[elliottkember]

Summary:

This line of the documentation says that onShouldBlockNativeResponder in PanResponder only works on Android. However, I just tried it and it seems to be working very nicely on iOS.

Changelog:

[IOS] [FIXED] - Inconsistent documentation: onShouldBlockNativeResponder works on iOS

Test Plan:

Code comment change only. No functional changes should require no testing

[javache]

While you can definitely set the property, the result is ignored on iOS.

• Old arch: https://github.com/facebook/react-native/blob/main/packages/react-native/React/Modules/RCTUIManager.m#L1448
• New arch: https://github.com/facebook/react-native/blob/main/packages/react-native/React/Fabric/Mounting/RCTMountingManager.mm#L284

[github-actions]

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[elliottkember]

@javache This prop is not being completely ignored, as changing it to return true or false directly alters the behaviour in iOS.

For context, I am using a PanResponder inside a react-navigation native modal stack, and this allows me to use pan responders there. Without setting this property, the gestures bubble up to the (RNScreens) native modal view. Without this callback, the modal is dismissed if I pull down. The events are bubbling up to the native view.

It may be ignored at the native level, but is this perhaps related to these lines which handle this in the JS level? I don't know enough about the workings to be absolutely sure. I may even be using the wrong prop – but so far this callback works for me on iOS and is extremely useful!

[elliottkember]

OK, I've got it @javache – I figured out what caused this to work for me!

It turns out I was using a library that implements react-native-gesture-handler and this was handling the gestures for me. I don't know how yet, but using onShouldBlockNativeResponder made that PanGestureHandler reliably pick up and handle the events, which I thought was really strange.

For now, the solution will be to wrap my pan responder in a PanGestureHandler so that I can use pan responders in modals. I'll see if there is any other documentation on it.

[elliottkember]

Yep – react-native-gesture-handler overrides setJSResponder which causes this prop to start working. (Relevant issue props to @thomasttvo for finding it).

Last question – is there a deliberate reason this isn't implemented? Can/should it be? It's nice to finally be able to put pan responders into modal views like this. The gesture handler is a fine workaround, just wondering whether there's some deliberate decision not to implement this in RN itself.

Thank you!

[javache]

Yep – react-native-gesture-handler overrides setJSResponder which causes this prop to start working. (Relevant issue props to @thomasttvo for finding it).

Overriding UIManager methods like this is extremely fragile. This is guaranteed to break in the new architecture.

Last question – is there a deliberate reason this isn't implemented? Can/should it be? It's nice to finally be able to put pan responders into modal views like this. The gesture handler is a fine workaround, just wondering whether there's some deliberate decision not to implement this in RN itself.

I think iOS' model for blocking other gestures is significantly different from how Android approaches this, it would be great to unify it though. We currently just have ad-hoc logic checking for responders, eg https://github.com/facebook/react-native/blob/main/packages/react-native/React/Views/ScrollView/RCTScrollView.m#L65-L75