Android 'Unable to add window — token null is not for an application' exception

Question

I get the following Android exception when I try to open a dialog. Can someone please help me understand what is going on and how can I fix this problem?

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Answer 1

I tried with this in the context field:

this.getActivity().getParent()

and it works fine for me. This was from a class which extends from "Fragment":

public class filtro extends Fragment{...