开发人员android OPENGL ES教程 - 黑屏

I am trying to learn about opengl es and followed the tutorial att android developer. First one really small example - they said that the screen would turn to a grey color. When I replicated the example and launced the app om my Samsung galaxy SIII - the screen become totaly black and the action bar on the topscreen where the app-name can be seen. So - no error - just a black colour covering almost the whole screen except the actionbar. Then on the extended example on developer android where shapes are supposed to be drawn - EXACTLY the same scenario - just a black screen - no errors.I am trying to learn about opengl es and follow