There is a function for that in System.Windows.Input.KeyInterop static class. Try:
var inputKey = KeyInterop.KeyFromVirtualKey((int)formsKey);
It works because System.Windows.Forms.Keys enumeration members and Win32 virtual key codes has the same numerical values (by design), while WPF's System.Windows.Input.Key do not (also by design).
This will definitly work much faster than Matt's format-then-parse method. And probably more correct in corner cases, like when literal names of the same logical key might differ slightly in the two enums.
Finally if you need to convert in the opposite direction use:
var formsKey = (System.Windows.Forms.Keys)KeyInterop.VirtualKeyFromKey(inputKey);
Regards,
- Levi