UIViewController中的集合視圖可選的展開崩潰

Question

Swift還很新，閱讀了解「最佳實踐」，我試圖重構一些簡單的代碼，但無法繞過選項並將簡單的UICollectionView放在一個簡單的代碼中UIViewController。

我有什麼，它的工作原理

class AddFriendsController: UIViewController { 

    fileprivate let cellId = "cellId" 

    override func viewDidLoad() { 
     super.viewDidLoad() 

     navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(handleCancel)) 

     let layout = UICollectionViewFlowLayout() 
     layout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10) 
     layout.itemSize = CGSize(width: 111, height: 111) 

     let collectionViewTest = UICollectionView(frame: self.view.frame, collectionViewLayout: layout) 
     collectionViewTest.delegate = self 
     collectionViewTest.dataSource = self 
     collectionViewTest.register(UserFriendCell.self, forCellWithReuseIdentifier: cellId) 

     view.addSubview(collectionViewTest) 
     collectionViewTest.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true 
     collectionViewTest.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true 
     collectionViewTest.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true 
     collectionViewTest.heightAnchor.constraint(equalTo: view.heightAnchor).isActive = true 
    } 

    @objc private func handleCancel() { 

     self.dismiss(animated: true, completion: nil) 
    } 

} 

extension AddFriendsController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout { 

    func numberOfSections(in collectionView: UICollectionView) -> Int { 

     return 2 
    } 

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int { 

     return 9 
    } 

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 

     let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! UserFriendCell 

     return cell 
    } 
} 

我想什麼它是像

class AddFriendsController: UIViewController { 

    fileprivate let cellId = "cellId" 
    private weak var collectionViewTest: UICollectionView? 
    private weak var layout: UICollectionViewFlowLayout? 

    override func viewDidLoad() { 
     super.viewDidLoad() 

     navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(handleCancel)) 

     layout = UICollectionViewFlowLayout() 
     layout!.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10) 
     layout!.itemSize = CGSize(width: 111, height: 111) 

     collectionViewTest = UICollectionView(frame: self.view.frame, collectionViewLayout: layout!) 
     collectionViewTest!.delegate = self 
     collectionViewTest!.dataSource = self 
     collectionViewTest!.register(UserFriendCell.self, forCellWithReuseIdentifier: cellId) 

     view.addSubview(collectionViewTest!) 
     collectionViewTest!.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true 
     collectionViewTest!.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true 
     collectionViewTest!.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true 
     collectionViewTest!.heightAnchor.constraint(equalTo: view.heightAnchor).isActive = true 
    } 

    @objc private func handleCancel() { 

     self.dismiss(animated: true, completion: nil) 
    } 
} 

extension AddFriendsController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout { 

    func numberOfSections(in collectionView: UICollectionView) -> Int { 

     return 2 
    } 

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int { 

     return 9 
    } 

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 

     let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! UserFriendCell 

     return cell 
    } 
} 

這樣做是因爲我想嘗試從應用「最佳實踐」開始學習斯威夫特，即從我所瞭解的這種情況下儘可能多的東西private和weak ify /「optionalize」views/outlets，以避免保留c ycles。

問題

應用崩潰，因爲爆炸在layout!.sectionInset水平展開一個零。

任何善良的靈魂願意開導我嗎？

在此先感謝。

Answer 1

看起來像你聲稱你佈局爲弱。如果你改變它強壯，即只是刪除弱，那麼你應該沒問題。

同樣適用於您的CollectionView。

同樣作爲一種風格問題，你可以聲明你的佈局和你的collectionView被隱式解開，而不是每次解開包裝。

因此，像private var layout: UICollectionViewFlowLayout!

Answer 2

沒有與你的代碼的問題。

如果你正在服用的變量作爲可選像

private weak var layout: UICollectionViewFlowLayout? 

然後用力才解開你應該確認這是不爲零。所以在這條線上它會導致崩潰，因爲你正在試圖強行解開一個實際上爲零的變量。

layout!.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10) 

因此，如果你想要這樣做，而不添加非零檢查比你應該寫。

layout?.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10) 

但在這裏你的代碼也是錯誤的，因爲，因爲弱引用是隻是一個指向對象，不保護對象由ARC被釋放你不應該採取變量弱。

在這裏你想UICollectionViewFlowLayout和UICollectionView通過了UIViewController的生命週期，所以你不應該把它當成弱。

所以你應該將兩者都定義爲under。

private var collectionViewTest: UICollectionView! 
    private var layout: UICollectionViewFlowLayout! 

OR

private var collectionViewTest: UICollectionView? 
    private var layout: UICollectionViewFlowLayout?