Method 1. Non-inheriting the main Activity

1. Writing JAR file in Android Studio

• 1. Create a new class and write your own method (here’s how to create the file and update the media library

package com.pico.jartest;
import …;

public class JarClass {
    public void updateFile(Context context, String fullFileName) {
            Log.e(TAG, "updateFile: ");
            Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
            intent.setData(Uri.fromFile(new File(fullFileName)));
            context.sendBroadcast(intent);
    }
 }

• 2. Add the following code on the app-> build.gradle root node, which is the same level as android and dependencies

task createJarDebug(type: Jar,dependsOn: ['build']) {
  baseName "test"
  from 'build/intermediates/javac/debug/compileDebugJavaWithJavac/classes'
  include('**')
  exclude('**/R.class')
  exclude('**/R$*.class')
  exclude('**/BuildConfig.class')
  exclude('**/MainActivity.class')
  exclude('**/MainActivity$*.class')
}

• 3. In Terminal, type gradlew createJarDebug (you need to generate the obguile package, type gradlew createJarDebug proguard)

If prompted build success, the package succeeds

Jar package path: app/build/libs/test.jar

Copy to Unity engineer and tell them package name. Class name, interface name

2. Use the JAR file in Unity project

• 1. Copy the Jar package to the Assets/Plugins/Android/ directory
• 2. Create a new script, use “PackageName.ClassName” to initialize object of the class defined in JAR file.

public class filetest : MonoBehaviour {
  string fullFileName;
  AndroidJavaObject updateFileManager;
  AndroidJavaObject ActivityContext;

  private void Start()
  {
    fullFileName = "/storage/emulated/0/Download/update.txt";
    updateFileManager = new AndroidJavaObject("com.picovr.updateanyfile.UpdateManager");
    ActivityContext = new AndroidJavaClass("com.unity3d.player.UnityPlayer").GetStatic<AndroidJavaObject>("currentActivity");
  }
  public void updateFile()
  {
    updateFileManager.Call("updateFile", ActivityContext, fullFileName);
  }
}