【发布时间】：2017-02-16 10:51:05
【问题描述】：
对于 Swift 来说还是很陌生，并且已经阅读/了解了“最佳实践”，我正在尝试重构一些简单的代码，但无法将我的头脑围绕可选选项并将简单的 UICollectionView 放在 UIViewController 中。
我有什么，什么有效
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
}
}
我希望它是什么样的
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
}
}
这样做是因为我想在学习 Swift 时从一开始就尝试应用“最佳实践”，即根据我在这种情况下的理解，尽可能多地制作 private 和 weakify/"optionalize" 视图/outlets 以避免保留循环。
问题
由于 bang 在 layout!.sectionInset 级别展开 nil，应用程序崩溃。
哪位好心人愿意开导我？
提前致谢。
【问题讨论】：
-
为什么你的布局属性很弱？它是否保留了视图控制器？为什么不从声明中初始化它？所以你不需要强制解包：
private let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
标签： ios swift uiviewcontroller swift3 uicollectionview