Android on BlueHour

C#, Java, and Cpp Communication in Unity

Thu, 12 Sep 2024 00:00:00 +0000

This post covers four things:

How C# calls Java functions in Unity.
How Java calls C++ through JNI.
How C++ under JNI calls Java.
How Java calls Unity’s C#.

CSharp Call Java

Use Unity’s AndroidJavaObject, and pass the Java class object into the constructor. The format is the package name followed by the class name.

For example, in Java:

package com.example.jni;

public class ExampleJavaClass {
	// Function with no return value
	void TestFuncVoid(int a) { /* ... */ }
	// Function with a return value
	int TestFuncInt(int a) { /* ... */ }
}

In CSharp, write it like this:

Cross-Compiling C++ for Android Without Android Studio

Sun, 17 Dec 2023 00:00:00 +0000

AndroidCppCrossCompile

Android Studio has quite a few bugs, and the C++ development experience is not exactly great. A lot of the time, when we need to do JNI development or pure C++ development, we do not really want to do it inside Android Studio. So we need an environment for cross-compiling C++ programs for Android without relying on Android Studio.

Next, I will use CMake to build the whole workflow. First, the preparation: you must download the NDK, because we need to use the NDK toolchain. The version I use here is r23c.

Using Arm64 Assembly on Android

Mon, 16 Oct 2023 00:00:00 +0000

AndroidAsm

First, create an Android Studio JNI project. By default, the project will generate a C++ file that calls a native function from the Java side to display a string.

The function generated on the Cpp side uses static binding, so the function name is extremely long and not very pleasant to look at. Let’s change it to dynamic binding first. Start by renaming that verbose function.

JNIEXPORT jstring JNICALL StringFromJNI(JNIEnv *env, jclass clazz)
{
    std::string hello { "Hello World From JNI" };
    return env->NewStringUTF(hello.c_str());
}

Next, implement dynamic binding. Add a function called JniOnLoad to the Cpp file, and load the native function from the Java side inside this function.