Userdefaults Tableview placemark Swift 3 - swift

Question

I am using uitableview. I am trying to save the placemark when i have selected a cell. From the code below i have added a tableview and when i select a cell the placemark will be shown. But i'm having trouble saving it because when i go to another view controller and go back it doesn't show. I have researched and find that i need to use UserDefaults but i have no clue how to use it. can someone point me how can i achieve this. Thanks
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell")
let contactsCell = app.helper.contacts[indexPath.row]
cell!.textLabel?.text = contactsCell
return cell!
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let contactToCall = app.helper.contacts[indexPath.row]
app.helper.contactSelected = contactToCall
if let cell = tableView.cellForRow(at: indexPath) {
if cell.isSelected {
cell.accessoryType = .checkmark
}
}
}
func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
if let cell = tableView.cellForRow(at: indexPath) {
cell.accessoryType = .none
}
}

Answer 1

You don't need UserDefaults unless you want to maintain state after the app has been closed and restarted, and once you start storing user defaults, you're likely to want to store more - so it makes sense to create a defaults data class to store the selected index and any other 'stuff' you may need.
In this example, I'm going to load the defaults on viewDidLoad and store the defaults on each select / deselect. If you have other values stored, you should have additional storage calls.
Create a class for storing your data
class MyDefaultsData : NSObject, NSCoding
{
var selectedIndexPath : IndexPath?
var otherStuff : String?
override init()
{
// you can set up default values here if you need them
selectedIndexPath = nil
otherStuff = nil
}
// archiving code
func encode(with aCoder: NSCoder)
{
// you can't store IndexPath directly, so split it into row and section
if selectedIndexPath == nil
{
// set invalid values which we can identify later
aCoder.encode(-1, forKey: "indexSection")
aCoder.encode(-1, forKey: "indexRow")
}
else
{
aCoder.encode(selectedIndexPath!.section, forKey: "indexSection")
aCoder.encode(selectedIndexPath!.row, forKey: "indexRow")
}
aCoder.encode(otherStuff, forKey: "otherStuff")
}
required init(coder aDecoder: NSCoder)
{
let indexSection = aDecoder.decodeInteger(forKey: "indexSection")
let indexRow = aDecoder.decodeInteger(forKey: "indexRow")
if indexSection != -1 && indexRow != -1 // if no row is selected, these values will both be -1
{
selectedIndexPath = IndexPath(row: indexRow, section: indexSection)
}
else
{
selectedIndexPath = nil
}
self.otherStuff = aDecoder.decodeObject(forKey: "otherStuff") as? String
}
}
Define a variable of your default data within the ViewController
var defaultData = MyDefaultsData()
Load the data in your viewDidLoad
override func viewDidLoad()
{
loadDefaults()
}
func loadDefaults()
{
var dataDefaults : MyDefaultsData?
if let data = UserDefaults.standard.object(forKey: "NSDefaultsTest") as? Data
{
dataDefaults = NSKeyedUnarchiver.unarchiveObject(with: data) as? MyDefaultsData
self.defaultData.otherStuff = dataDefaults?.otherStuff ?? "No value found"
self.defaultData.selectedIndexPath = dataDefaults?.selectedIndexPath
}
}
then you use that default data within cellForRowAt
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell")
let contactsCell = app.helper.contacts[indexPath.row]
cell!.textLabel?.text = contactsCell
// set or clear the checkmark
if selectedIndexPath == indexPath
{
cell.accessoryType = .checkmark
}
else
{
cell.accessoryType = .none
}
return cell!
}
When you change the selected row, you need to reload both the previous selected row (if any) and the currently selected row, to get the checkmark drawn
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)
{
let previousIndexPath = defaultData.selectedIndexPath
if previousIndexPath != indexPath
{
defaultData.selectedIndexPath = indexPath
}
else
{
defaultData.selectedIndexPath = nil
}
storeDefaults()
if previousIndexPath != nil
{
tableView.reloadRows(at: [previousIndexPath!], with: .automatic)
}
if defaultData.selectedIndexPath != nil
{
tableView.reloadRows(at: [defaultData.selectedIndexPath!], with: .automatic)
}
}