Get current Android activity and init an Android object from Unity

unityPlayer.cs

AndroidJavaObject localMediaPlayer = null;

using (AndroidJavaClass javaUnityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer"))
{
    using (currentActivity = javaUnityPlayer.GetStatic<AndroidJavaObject>("currentActivity"))
    {
        localMediaPlayer = new AndroidJavaObject("my/plugin/vr/ExoPlayerBridge", currentActivity);

        if (localMediaPlayer != null)
        {
            // Do some work with your java object outside the Android UI thread
            localMediaPlayer.Call("addSubtitles", subtitleURL);
            
            currentActivity.Call("runOnUiThread", new AndroidJavaRunnable(() =>
            {
                // Do some work on Android UI thread
                localMediaPlayer.Call("prepare", true);
            }));
        }
    }
}