Welcome to the Wefugees community and thank you for your question.
I'm not sure if this is going to work. In order to come to Germany you need a visa. Having someone that invites you, might give you a better chance to get such a visa because they will work a guarantor that covers expenses that might arise during your stay. But since you are a refugee in Uganda, German authorities might assume that you don't intend to go back after your visa expired. In this case it can happen that they refuse to give you a visa even though you are having an invitation and a guarantor.