Swift Compiler Warning : Result of call to 'save(defaults:)' is unused - ios

Question

So my table view is not loading anything and I think it's because of this warning that I get. It saids the save function is not being used so how can it load something that is not saved. What I am saving is the indexPath and Section of the row that the user selected via a button action in the row.
Warning:
Result of call to 'save(defaults:)' is unused
Code:
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 Class for 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
}
}
Other code I'm using:
// 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
}
Saving it with:
saveSorting() { "\($0)" }
Loading it in ViewDidLoad:
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()
}
Loading Code:
// 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

The DataHandling instance's save(defaults:) function technically returns a value, even if you don't use it. To silence this warning, assign it to _ to signify that you don't intend to use the result value, e.g.:
_ = ordering.save(defaults: indexPath.defaultsKey)
or
let _ = ordering.save(defaults: indexPath.defaultsKey)
Just to be clear, this is almost definitely not why your tableview is not loading data. It should be pretty insignificant. The indexPath.defaultsKey is being saved (assuming the API works).