Hey there! I totally get that integrating a JNI-based .so file when you don’t have native code experience can feel super overwhelming—especially after digging through tons of resources that don’t quite fit your scenario. Let’s break this down step by step, using the original app’s code as your cheat code to make this smooth.

First, dig into the original app’s project structure to find where the .so files live. In Android projects, they’re usually in either src/main/jniLibs (the standard location) or a libs folder. You’ll see subfolders for different CPU architectures like armeabi-v7a, arm64-v8a, x86, etc.

• Copy all these architecture folders (and the .so files inside) into your own app’s src/main/jniLibs directory. If that folder doesn’t exist, just create it.
• Make sure you don’t mix up architectures—if the original app only includes arm64-v8a and armeabi-v7a, don’t add extra ones your app doesn’t need.

JNI works by binding Java native methods to the code in the .so file, and that binding relies on the exact package name, class name, and method signatures from the original app. So:

• Search the original app’s code for any Java class that has the native keyword. It’ll look something like this:

package com.originalapp.nativeutils; // This package name MUST stay the same!

public class NativeHelper {
    // Load the .so file—note the name here is the .so filename without "lib" prefix and ".so" suffix
    // e.g., if your file is libmylibrary.so, use "mylibrary"
    static {
        System.loadLibrary("mylibrary");
    }

    // These are the native methods you’ll call from your app
    public native String fetchSecretValue();
    public native void initialize(String appId, Context context);
}

• Copy this entire class (and any related helper classes it uses) into your own app, keeping the package name identical. If you change the package name, the JNI binding will break, and you’ll get an UnsatisfiedLinkError—trust me, this is a super common pitfall.

The .so file might depend on specific app settings or permissions that the original app uses. Check these places:

• AndroidManifest.xml: Look for permissions the original app declares (like READ_EXTERNAL_STORAGE, INTERNET) and add any that are relevant to your use case of the .so file. Also, check if there are any <meta-data> tags that the native code relies on.
• build.gradle (Module level): Look for NDK-related configs, like:

android {
    defaultConfig {
        ndk {
            abiFilters 'armeabi-v7a', 'arm64-v8a' // Match this to the architectures of your .so files
        }
    }
}

Copy this NDK config into your own build.gradle to ensure your app only builds for architectures you have .so files for.

Now, figure out how the original app actually calls those native methods. For example:

• Does it initialize the native code in the Application class’s onCreate() method?
• Does it pass specific parameters (like an app key, context, or file path) to the native methods?
• Are there any setup steps (like creating a specific folder, loading a resource file) that happen before calling native methods?

Copy this exact flow into your app. If the original app calls NativeHelper.initialize("XYZ123", getApplicationContext()) on startup, you need to do the same—using the same parameters if they’re required for the .so to work.

If you run into crashes or errors, here are the most common fixes:

• UnsatisfiedLinkError: This means the app can’t find the native method. Double-check:
  • The package name/class name/method signatures match the original app exactly.
  • The System.loadLibrary call uses the correct name (no lib prefix or .so suffix).
  • The .so file is in the right architecture folder for your test device.
• Native Crash (SIGSEGV): This usually means the native code is getting invalid input (like a null context, wrong parameter type). Make sure you’re passing the same data types and values as the original app.
• Missing Dependencies: Sometimes .so files depend on other .so files. Check the original app’s jniLibs folder for any other .so files you might have missed, and copy those over too.

You’ve got this—since you have the original app’s code, you’re already ahead of the game. Just mirror what they did, and you’ll have that .so integrated in no time.

内容的提问来源于stack exchange，提问作者nevsnirG