Presented when the controller's view background color alpha is not 1 o'clock, why does the new controller turn into a black background?

Navigationcontroller and the View Controllers is designed in such a-in-one view controller may show at a time. When a new view controller is pushed/presented the previous view controller would be hidden by the system. So when you reduce the modal view's alpha you'll possibly see the window's BackgroundColor (the black color you see NOW) .

If you want a translucent view to slide-in over the main view, you can add the view as the SubView of main view and Animat E it using UIView animations.

Presented a new controller if the controller's view background color alpha is not 1 o'clock, why it becomes a black background.