Why measure on Android doesn't calculate relative position?

[janlat]

measure on Android is hardcoded to return 0 for both x and y. Are there any technical reasons why this wasn't implemented?

[tomekzaw]

How do you know it's hardcoded to return 0? As far as I know it's not.

[janlat]

It always returns 0 for me, so I tried debugging a bit and found this:

react-native-reanimated/android/src/main/java/com/swmansion/reanimated/NativeMethodsHelper.java

Lines 32 to 34 in 8933a00

	float result[] = new float[6];
	result[0] = result[1] = 0;
	for (int i = 2; i < 6; ++i) result[i] = PixelUtil.toDIPFromPixel(buffer[i - 2]);

but maybe I'm missing something here

[tomekzaw]

Well, didn't notice this before 😅 I will investigate this further and I will let you know.

[tomekzaw]

I'm back with the results.

Example:

Library:

• React Native - ref.current.measure(...), https://reactnative.dev/docs/direct-manipulation#measurecallback
• Reanimated - measure(animatedRef), https://docs.swmansion.com/react-native-reanimated/docs/api/nativeMethods/measure/

Platform	Architecture	Library	Result
Android	Paper	React Native	{"height": 80, "pageX": 20, "pageY": 256, "width": 80, "x": 0, "y": 0}
Android	Paper	Reanimated	{"height": 80, "pageX": 20, "pageY": 256, "width": 80, "x": 0, "y": 0}
Android	Fabric	React Native	{"height": 80, "pageX": 20, "pageY": 256, "width": 80, "x": 20, "y": 30.18181800842285}
Android	Fabric	Reanimated	{"height": 80, "pageX": 20, "pageY": 256, "width": 80, "x": 20, "y": 30.18181800842285}
iOS	Paper	React Native	{"height": 80, "pageX": 20, "pageY": 263, "width": 80, "x": 20, "y": 30}
iOS	Paper	Reanimated	{"height": 80, "pageX": 20, "pageY": 263, "width": 80, "x": 20, "y": 30}
iOS	Fabric	React Native	{"height": 80, "pageX": 20, "pageY": 263, "width": 80, "x": 20, "y": 30}
iOS	Fabric	Reanimated	{"height": 80, "pageX": 20, "pageY": 263, "width": 80, "x": 20, "y": 30}

It looks like in each case Reanimated matches the output from React Native, which is the expected behavior.

[janlat]

Huh, interesting. Another reason to migrate to the new architecture I guess 😄
Do you think it's worth mentioning in the docs?

[tomekzaw]

Huh, interesting. Another reason to migrate to the new architecture I guess 😄

Maybe it's worth submitting an issue in react-native repo? Technically, the behaviour should be consistent across the architectures.

Do you think it's worth mentioning in the docs?

Since the behavior is identical to the original from React Native, I don't think it's urgent. But feel free to open a PR if you find this piece of information useful.