Android : How Can I Get A Dialog Style Activity Window To Fill Screen?

I am using an activity with the dialog theme set, and I want it to be full screen. I tried all sorts of things, even going through the WindowManager to expand the window to full width and height manually, but nothing works. Apparently, a dialog window (or an activity with the dialog theme) will only expand according to its contents, but even that doesn't always work. For instance, I show a progress bar circle which has width and height set to FILL_PARENT (so does its layout container), but still, the dialog wraps around the much smaller progress bar instead of filling the screen. There must be a way of displaying something small inside a dialog window but have it expand to full screen size without its content resizing as well?