[wix-users] Check if product is installed when using custom UI

[Хакер Математики]

Hello,

I am writing a MSI installer using WixSharp.

Standard behavior (when using built-in UI) is, when the same version 
installed, to abort setup and display warning message. When I re-build 
installer AND application, the installer with built-in UI does an upgrade.

Now I'm moving to a custom UI. However, even if the same version of 
product is already installed, the installer still runs my custom UI. So 
I have to somehow re-create or emulate standard check and display the 
warning message I am so happy with.

How do I do such a check with custom UI?

BR,
Andrei Samoylov