Swift 编译器警告：调用'save(defaults:)'的结果未使用

Question

所以我的表视图没有加载任何内容，我认为这是因为我得到的这个警告。它说保存功能没有被使用，所以它怎么能加载没有保存的东西。我保存的是用户通过行中的按钮操作选择的行的索引路径和部分。

警告：

调用"保存（默认值：）"的结果未使用

法典：

func saveSorting(_ dataIdBlock: (Any) -> String) {
    guard let items = self.items else { return }
    for (section, rows) in items.enumerated() {
        for (row, item) in rows.enumerated() {
            let indexPath = IndexPath(row: row, section: section)
            let dataId = dataIdBlock(item)
            let ordering = DataHandling(dataId: dataId, indexPath: indexPath)
            // Warning is here
            ordering.save(defaults: indexPath.defaultsKey)
            }
        }
    }
}

NSCoder 类用于数据处理/排序.save

DataHandling.swift
class DataHandling: NSObject, NSCoding {
var indexPath: IndexPath?
var dataId: String?
init(dataId: String, indexPath: IndexPath) {
    super.init()
    self.dataId = dataId
    self.indexPath = indexPath
}
required init(coder aDecoder: NSCoder) {
    if let dataId = aDecoder.decodeObject(forKey: "dataId") as? String {
        self.dataId = dataId
    }
    if let indexPath = aDecoder.decodeObject(forKey: "indexPath") as? IndexPath {
        self.indexPath = indexPath
    }
}
func encode(with aCoder: NSCoder) {
    aCoder.encode(dataId, forKey: "dataId")
    aCoder.encode(indexPath, forKey: "indexPath")
}
func save(defaults box: String) -> Bool {
    let defaults = UserDefaults.standard
    let savedData = NSKeyedArchiver.archivedData(withRootObject: self)
    defaults.set(savedData, forKey: box)
    return defaults.synchronize()
}
convenience init?(defaults box: String) {
    let defaults = UserDefaults.standard
    if let data = defaults.object(forKey: box) as? Data,
        let obj = NSKeyedUnarchiver.unarchiveObject(with: data) as? DataHandling,
        let dataId = obj.dataId,
        let indexPath = obj.indexPath {
        self.init(dataId: dataId, indexPath: indexPath)
    } else {
        return nil
    }
}
class func allSavedOrdering(_ maxRows: Int) -> [Int: [DataHandling]] {
    var result: [Int: [DataHandling]] = [:]
    for section in 0...1 {
        var rows: [DataHandling] = []
        for row in 0..<maxRows {
            let indexPath = IndexPath(row: row, section: section)
            if let ordering = DataHandling(defaults: indexPath.defaultsKey) {
                rows.append(ordering)
            }
            rows.sort(by: { $0.indexPath! < $1.indexPath! })
        }
        result[section] = rows
    }
    return result
  }
}

我正在使用的其他代码：

// Number of Rows in Section
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return self.items?[section].count ?? 0
}
// Number of Sections
func numberOfSections(in tableView: UITableView) -> Int {
    return self.items?.count ?? 0
}

保存方式：

saveSorting() { "($0)" }

在ViewDidLoad中加载它：

func fetchData() {
    // Load Data from Server to testArray
    retrieveData()
    // request from remote or local
    data = [testArray]
    // Update the items to first section has 0 elements,
    // and place all data in section 1
    items = [[], data ?? []]
    // apply ordering
    applySorting() { "($0)" }
    // save ordering
    saveSorting() { "($0)" }
    // refresh the table view
    myTableView.reloadData()
}

加载代码：

// Loading
func applySorting(_ dataIdBlock: (Any) -> String) {
    // get all saved ordering
    guard let data = self.data else { return }
    let ordering = DataHandling.allSavedOrdering(data.count)
    var result: [[Any]] = [[], []]
    for (section, ordering) in ordering {
        guard section <= 1 else { continue } // make sure the section is 0 or 1
        let rows = data.filter({ obj -> Bool in
            return ordering.index(where: { $0.dataId == .some(dataIdBlock(obj)) }) != nil
        })
        result[section] = rows
    }
    self.items = result
}

Answer 1

从技术上讲，DataHandling实例的 save(defaults:) 函数会返回一个值，即使您不使用它也是如此。要使此警告静音，请将其分配给_以表示您不打算使用结果值，例如：

_ = ordering.save(defaults: indexPath.defaultsKey)

或

let _ = ordering.save(defaults: indexPath.defaultsKey)

需要明确的是，这几乎肯定不是您的表视图不加载数据的原因。它应该是微不足道的。正在保存indexPath.defaultsKey（假设 API 有效）。