Control over app activities in android

As far as I know, there is no way to control over the activities occurring in an app in android phones unless the application that you want to log/monitor is written by you.

I wonder is it really like that or is there any possible way to do this? For example, is it possible 开发者_如何学编程to control over emails which, let's say, who I sent an email to in an android phone?

It is not possible to "just log it". Some events are possible to catch in broadcast receivers in a logging application. The user will get notified by particular event sniffing when installing such an application, by approving the permissions request.

It's generally possible to add instrumentation for security purposes to apps where they interface to the sdk api's, either by modifying the platform (rooted phone) or by decompiling, modifying, and recompiling the app using apktool.

possible of course does not mean trivially easy.