Any idea why doesn't the "Main" screen work properly?

Vocaloid_Wallpapers.aia (1.7 MB)

Hello, I’m new to Android Builder. I know this is basically asking others to do the work for me, but I’m terribly confused here and don’t know what to do. The Main screen is supposed to be a two-column wallpaper gallery, but only the background appears. I would really appreciate some help on how to make it work, thank you.