Perform functions during screen transition with swift

For modal screen transitions, the transition source ViewController can be retrieved in the UIViewController class property presentingViewController.
If the transition source ViewController is BaseViewController and the method you want to call baseViewController is func doAnything(),

 iflet controller=self.presentingViewController as? BaseViewController {
    controller.doAnyThing()
}

I want to run the function of screen A when I return to screen A from screen B

Strictly speaking, it does not meet your requirements, as the code above will be executed before returning.I don't think that's a problem, but if there is a situation where it has to be "after closing", use the argument completion in dismissViewControllerAnimated().

let controller=self.presentingViewController as? BaseViewController
self.dismissViewControllerAnimated(true, completion:{
    controller?.doAnything()
})

If you use self.presentingViewController in the closure, it doesn't work well, so this is how it is written.

I think you can do it with the viewWillAppear function.

class ViewController:UIViewController {
    Override func viewWillAppear(_animated:Bool) {// Runs on return
        super.viewWillAppear(animated)
        // Code here
    }
}

Note: However, with this method, it will also be executed when screen A is first displayed.
Therefore,

class ViewController:UIViewController {
    varisBack=false
    Override func viewWillAppear(_animated:Bool) {// Runs on return
        super.viewWillAppear(animated)
        // Code here
        ifisBack{
            // Code here
        }
        isBack.toggle()
    }
}

As shown in , you can define the variables and make sure that you returned using the conditional branch.
However, in this way,

C->A->B

C->*A->C->*/A

If you transition in this order, you will see WillAppear with the * mark, but if you return to the / mark, you will have to do something else, such as pass the value from B.