顶层ViewController的获取

在开发的时候，为了减少耦合，将View进行拆分时，有时候会碰到ViewController上加载另一个ViewController的View。这时我们需要获取当前最上层的ViewController，在最上层的ViewController进行push，present等操作。

import Foundation
import UIKit

extension UIApplication {
    
    static func topViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController)-> UIViewController? {
        
        if let navi = base as? UINavigationController {
            return topViewController(base:navi.visibleViewController)
        }
        
        if let tab = base as? UITabBarController {
            let moreNavigationController = tab.moreNavigationController
            
            if let top = moreNavigationController.topViewController, top.view.window != nil {
                return topViewController(base:top)
            } else if let selected = tab.selectedViewController {
                return topViewController(base:selected)
            }
        }
        
        if let presented = base?.presentedViewController {
            return topViewController(base:presented)
        }
        
        return base
    }
}