为什么我必须单击该行以显示图像，因为它已被加载？

I am on the assignment 4 of Stanford Course "Developing iOS 8 Apps With Swift" by Paul Hegarty. The assignment is developing an app searching Twitter to get some tweets and display them in a tweets table view. And if i click one row of the tweets table view, it segues to a detail table view which displays the hashtag, urls, user mentioned and attached media photos of the tweet in four sections. I am on the assignment 4 of Stanford Course "De