little tips to close overlay on SwiftUI

 This is about the architecture of SwiftUI.

Objective: I want to open and close little overlay message box.

When closed, I don't want to use system resource, and additionally I'll be happy if I can use onAppear and onDisappear.

Also, I want my closing animation work properly.

Implementation:

1. Use complete object destruction by defining 

func View.overlay(_ view: View?) -> View {
    if view == nil{

        self

    }else{

        self.overlay(view)

    }

}

In this way, when I started closing animation by withAnimation{overlayView = nil}, the screen shows preview of the main view, so I see all the blinks and glitches.

2. opacity -> 0

By this method, I am worried that I cannot achieve the objective. It is wasting my resources and I think I cannot use onDisappear.

3. hidden(_ bool: Bool)

Define this function for View. This worked perfectly so I did not tested 2nd option. I think this is supposed to do, designed by Apple developers.

In this way, onAppear is called *when the mainview.overlay() is called * when overlay is unhidden *but not when overlay is not completely hidden but new appearance is called. onDisappear is called *when overlay is completely hidden (end of animation) *but not when overlay hiding animation is over but new overlay unhiding is called.