如何在Android项目中复用Windows平台C#类库，避免大量代码转译？

Great question! I’ve helped several developers tackle this exact problem—you absolutely don’t have to rewrite all that C# code to Java. Let’s walk through the most practical ways to reuse your classLibrary.dll in an Android project:

1. Go with .NET for Android (Formerly Xamarin.Android) #

This is the smoothest path if you’re okay sticking with the .NET ecosystem. Here’s how it works:

• First, adjust your C# library to target a cross-platform framework like .NET Standard 2.0+ (or .NET 6+/Android if you want to go all-in). Strip out any Windows-specific code (like stuff using System.Windows or Windows-only Bluetooth APIs) since those won’t run on Android.
• Create a .NET for Android project and reference your C# library directly. For platform-specific gaps (like the Bluetooth functionality you already built in Java), use interface-based design or dependency injection to swap in the Android-compatible implementation.
• Build the .NET for Android project into an Android Archive (.aar) file. This is the standard library format Android Studio uses, so you can import it directly into your Android Studio project as a dependency—no complex setup required.
• Bonus: .NET for Android uses Mono under the hood, so performance is on par with Java for most use cases, and you can debug your C# code directly in Visual Studio if you prefer that over Android Studio.

2. Compile C# to Native Android Libraries with Mono AOT #

If you want to avoid the .NET runtime overhead (or need tighter integration with native Android code), try Ahead-of-Time (AOT) compilation:

• Prep your C# library: Remove all Windows-specific dependencies and ensure your code is either platform-agnostic or uses conditional compilation for Android-specific logic.
• Use Mono’s tools to compile your DLL into a native .so library (Android’s equivalent of Windows DLLs). Tools like mkbundle or the Mono AOT compiler can convert your C# code into ELF-format shared libraries that Android can load natively.
• Write JNI bindings in Java: Create Java wrapper classes that use the Java Native Interface (JNI) to call into the compiled .so library. Package these Java classes and the .so file into an Android library module for use in Android Studio.
• Note: This approach requires some low-level JNI work, but it gives you full control over how your C# code interacts with Android’s native environment.

3. Leverage Unity as a Bridge (Since You Already Use It) #

Since you’ve already tested your Java Bluetooth plugin in Unity, this could be a quick win:

• Add your classLibrary.dll to your Unity project and make sure it plays nice with your existing Java Bluetooth plugin (Unity supports seamless interop between C# and Java).
• Export your Unity project as an Android Library (.aar) instead of a full app. This AAR will include both your C# code (compiled to Mono bytecode) and your Java Bluetooth plugin.
• Import the AAR into Android Studio as a dependency. You can then call into your C# library from Android Java/Kotlin code using Unity’s interop APIs, like AndroidJavaClass or AndroidJavaObject, to expose specific methods from your C# code to the Android layer.
• Heads-up: This adds the Unity runtime to your app, which increases the app size a bit, but it’s a great option if you’re already familiar with Unity’s Android build pipeline.

Key Things to Keep in Mind #

• Windows-Specific APIs: Any parts of your C# library that rely on Windows-only features (like Microsoft.Win32 or Windows Bluetooth APIs) won’t work on Android. You’ll need to abstract these sections and replace them with Android-compatible code (like your existing Java Bluetooth implementation).
• Performance: For computationally heavy tasks, the AOT compilation approach (option 2) will give you the best performance. For most general-purpose code, .NET for Android or Unity will perform just fine.
• Debugging: Debugging C# code in Android Studio can be trickier than Java/Kotlin. If you use .NET for Android, you can debug your C# code directly in Visual Studio. For Unity-based solutions, stick with Unity’s built-in debugger.

内容的提问来源于stack exchange，提问作者jib fashr