能够显示所有活动，但无法仅显示关注用户的活动。未定义的方法

I followed Michael Hartl's Rails Tutorial to implement a follower system similar to Twitter's (railstutorial.org). For now, I want to use this follower system to only display activities of users followed by the user currently logged in. I'm able to display all activities in the system on the /activities page with no issue. The Activities controller code that works is as follows:I followed Michael Hartl's Rails Tutorial to im