addWeeks method
Implementation
void addWeeks(int weeks) {
final hr = ptr.ref.vtable
.elementAt(48)
.cast<Pointer<NativeFunction<HRESULT Function(Pointer, Int32 weeks)>>>()
.value
.asFunction<int Function(Pointer, int weeks)>()(ptr.ref.lpVtbl, weeks);
if (FAILED(hr)) throw WindowsException(hr);
}