JNI can't find some Kotlin functions for SDK 24-26

[jpudysz]

What's happening?

Hey,

for older Android SDKs 24-26 JNI struggles to get class method. It throws error that there is no such method, which is obviously not true. It works fine for SDK greater than 26+.

I was able to reproduce it locally, but can't with Nitro example.
I use C++ bindings to store C++ lambda on Kotlin side. I'm using it for sync callbacks.

Removing private from registerPlatformListener_cxx fixes the issue.

Reproduceable Code

void JHybridNativePlatformSpec::registerPlatformListener(const std::function<void(const std::vector<UnistyleDependency>& /* dependencies */, const UnistylesNativeMiniRuntime& /* miniRuntime */)>& callback) {
    static const auto method = _javaPart->getClass()->getMethod<void(jni::alias_ref<JFunc_void_std__vector_UnistyleDependency__UnistylesNativeMiniRuntime::javaobject> /* callback */)>("registerPlatformListener_cxx"); // <- crashes here
    method(_javaPart, JFunc_void_std__vector_UnistyleDependency__UnistylesNativeMiniRuntime_cxx::fromCpp(callback));
  }

Relevant log output

Exception in HostObject::get for prop 'Unistyles': java.lang.NoSuchMethodError: no non-static method "Lcom/unistyles/NativePlatformAndroid;.registerPlatformListener_cxx

Device

Android Emulator with SDK 24-26

Nitro Modules Version

0.22.1

Nitrogen Version

0.22.1

Can you reproduce this issue in the Nitro Example app here?

No, I cannot reproduce the issue in the Example app

Additional information

• I am using Expo
• I am using Nitrogen (nitro-codegen)
• I have read and followed the Troubleshooting Guide.
• I created a reproduction PR to reproduce this issue here in the nitro repo. (See Contributing for more information)
• I searched for similar issues in this repository and found none.

[mrousavy]

Hm, I wouldn't understand why this suddenly fails. You can call private methods through JNI, that shouldn't make a difference at all.
In fact, I am doing it in NitroExample (in the react-native-nitro-image TestObject) quite a lot, and I even have an example that is almost identical to yours - a function with a callback:

nitro/packages/react-native-nitro-image/nitrogen/generated/android/kotlin/com/margelo/nitro/image/HybridTestObjectSwiftKotlinSpec.kt

Lines 246 to 251 in 4907639

	@DoNotStrip
	@Keep
	private fun callCallback_cxx(callback: Func_void): Unit {
	val __result = callCallback(callback)
	return __result
	}

That's private and can be called from C++/JNI just fine.

[mrousavy]

Why are you saying SDK 24-26 explicitly - does this not happen on minSdk 26 or higher?

Ah - so it works on minSdk 26+... That is even more weird, lol.

[mrousavy]

@jpudysz can you add @JvmName("registerPlatformListener_cxx") to your private func to see if that makes it work?

[mrousavy]

Potential fix: #534

[mrousavy]

And the last thing you can try is to add a @DoNotInline annotation to your private fun. See if that changes anything.

Appreciate your help here

[mrousavy]

I just merged this - but pls still try if @JvmName OR @DoNotInline work for you.

[jpudysz]

@JvmName + private didn't work.

same for @DoNotInline. It's getting weird. No idea why it fails for older SDKs.

[mrousavy]

Ah, shit.

[mrousavy]

I would need to reproduce this here in the example app, can I just set minSdk to 24 and it will be reproduceable?

[jpudysz]

You can repro it with my example on main branch. You can use expo-example. Adding private in generated files + prebuilding causes the issue.