Swift編譯器警告：調用'save（defaults :)'的結果未被使用

Question

所以我的表視圖沒有加載任何東西，我認爲這是因爲我得到這個警告。它說save函數沒有被使用，所以它如何加載一些沒有保存的東西。我保存的是用戶通過行中的按鈕操作選擇的行的indexPath和Section部分。

警告：

調用的結果 '保存（默認:)' 是未使用的

代碼：

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班DataHandling/ordering.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 

    } 

} 

其他代碼我使用：

saveSorting() { "\($0)" } 

在viewDidLoad中加載它：

// 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 
} 

與保存它

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() 
} 

加載代碼：

// 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

的DataHandling研究所ance的save(defaults:)函數在技術上會返回一個值，即使您不使用它。要消除此警告，將其分配給_，以表示你不打算使用的結果值，例如：

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

或

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

只是要清楚，這幾乎是肯定不會爲什麼你的tableview沒有加載數據。它應該是非常微不足道的。 indexPath.defaultsKey是正在保存（假設API工作）。