脱Auto Layout モーダル遷移編

## はじめに

最近コードでレイアウトを組んでいるのでその備忘録。ネット上にあまり情報がなかったので残しときます。改善点などがあればコメントして欲しいです。🙇‍♂️なお、外部ライブラリの`SnapKit`を使っています。

完成するアプリの動きとしては

![Simulator Screen Shot - iPod touch (7th generation) - 2020-12-18 at 02.32.11.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/549093/d1b74dc3-cc5d-6fe9-8be3-aad99a9d93ce.png) ![Simulator Screen Shot - iPod touch (7th generation) - 2020-12-18 at 02.32.18.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/549093/fd32fb1d-579e-ca2d-45a5-8c9ef4877660.png)


こんな感じになります。

## 一つ目の画面

中央にボタンを配置し、`present`でモーダル遷移するように`addTarget`の中に入れています。


`button`を`lazy`で遅延処理させているのは`buttonTapped`を読み込んでからインスタンス化させているからです。
```swift
import UIKit
import SnapKit

final class ViewController: UIViewController {

    lazy var button: UIButton = {
        let button = UIButton()
        button.setTitle("移動する", for: .normal)
        button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
        return button
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .blue
        navigationItem.title = "Left"
        self.view.addSubview(button)
        button.snp.makeConstraints { make in
            make.size.equalTo(100)
            make.center.equalToSuperview()
        }
    }
    
    @objc func buttonTapped() {
        print("ボタンが押された")
        let leftSecondVC = SecondViewController()
        self.present(leftSecondVC, animated: true, completion: nil)
    }
}

```

## 二つ目の画面

```swift
import UIKit

class SecondViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = .purple
    }

}
```

特に何もしてないです。が、`backgroundColor`で背景色を指定しないと挙動がわかりにくくなるので注意が必要です。

## SceneDelegate

コードが全部載っていると読みやすいと思うので全部載せます。(笑)

```swift
import UIKit

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let _ = (scene as? UIWindowScene) else { return }
        
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = ViewController()
            
            self.window = window
            window.makeKeyAndVisible()
        }
    }
//ここから変えてない
    func sceneDidDisconnect(_ scene: UIScene) {
        // Called as the scene is being released by the system.
        // This occurs shortly after the scene enters the background, or when its session is discarded.
        // Release any resources associated with this scene that can be re-created the next time the scene connects.
        // The scene may re-connect later, as its session was not necessarily discarded (see `application:didDiscardSceneSessions` instead).
    }

    func sceneDidBecomeActive(_ scene: UIScene) {
        // Called when the scene has moved from an inactive state to an active state.
        // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
    }

    func sceneWillResignActive(_ scene: UIScene) {
        // Called when the scene will move from an active state to an inactive state.
        // This may occur due to temporary interruptions (ex. an incoming phone call).
    }

    func sceneWillEnterForeground(_ scene: UIScene) {
        // Called as the scene transitions from the background to the foreground.
        // Use this method to undo the changes made on entering the background.
    }

    func sceneDidEnterBackground(_ scene: UIScene) {
        // Called as the scene transitions from the foreground to the background.
        // Use this method to save data, release shared resources, and store enough scene-specific state information
        // to restore the scene back to its current state.
    }
}


```