Get keyWindow from UIApplication, not AppDelegate.

[Moriquendi]

There's no requirement that AppDelegate should have window property. It's how Xcode project is generated by it's not mandatory.
In my case, the app crashes because I hold window somewhere else and SVProgressHUD accesses unavailable selector.

[honkmaster]

We had this solution a few releases / a few years ago. However, we switch to using delegate.window as .keyWindow may not always be the delegate's window, where we want to add the hud. You can search closed issues for this. An option would be to make the window property accessible, with .window as default.