How to use callback function of Android?

I have known use AndroidJavaObject and AndroidJavaClass to call Android API, but how to use callback function of Android, For example ‘onActivityResult’? Thank you.

I already find a way to implement this function: build a new android project and import the libmono.so and libunity.so, now you can call callback function in new project, and in unity project, use AndroidJavaObject and AndroidJavaClass to get the results.