Windows应用商店应用，网格视图项目不显示

i'm working on a windows 8 app but i'm new to WPF. I've spend a good day on this but can't figure out why it doesn't work. Basically I am trying to create a grid view of some images with text at the top. But only a gradient filled box is displayed, no text or image.i'm working on a windows 8 app but i'm new to W