无法在旋转时获得背景渐变填充整个屏幕?

I have a background gradient that draws nicely when the screen is initially rendered in portrait mode. However, when the device is rotated to landscape mode, the right 40% of the screen is black (i.e. the background is not drawn on the part of the screen that wasn't previously drawn). I don't know how to get the background to redraw to fill the entire screen.I have a background gradient that draws nicely