Create Circles on a Map dynamically

Hello guys, I need to create dynamically circles (but may be interesting also for polygons and rectangles) on a map as is possible to do with markers. In the mean time I am searchin examples about how to loading features using a GEOJson, a url containing GEOJson data and loading a description to see if in practice it may be a viable solution also because from the help seems that can not create circles using Featurecollection1.FeatureFromDescription.
At the moment I create some circles, more then I think I will use, setting them to the North Pole coordinates and then, instead to create dynamically the circle when needed, I find the first not used circle and modify its coordinates and other needed data. But... it is not a very elegant solution.
N.B. I use an extension to create dynamically AI2 components as buttons, labels and so on but unfortunately it does not work with circles on a map.

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An alternative might be to create a runtime marker, and set it's image to an image of a circle and set its size accordingly. You could do the same for rectangles and other shapes.