Proper way to get swift dictionary item index - ios

Question

I have dictionary in my app written in Swift
var cities: [String: String] = ["":"not specified", "ny":"New York", "la":"Los Angeles", "sf":"San Francisco"]
I use this dictionary to build pickerView. When user selects one of this items - city code is saving to device memory.
When user opens app next time I want pickerView to show saved city. How should i do it?

Answer 1

You can find the index of a key in a dictionary with higher-order functions:
let desiredKey = "ny"
let pos = x.enumerate().filter { (pair: (index: Int, element: (String, String))) -> Bool in
return pair.element.0 == desiredKey
}.map { (pair: (index: Int, element: (String, String))) -> Int in
return pair.index
}
pos is an Optional(Int) containing the position of "ny" in the current iteration order of the dictionary.
Store the value of the key somewhere (say, in user defaults), then retrieve it, get the index of the key-value pair using the code above, and pass to selectedRowInComponent: of your picker view.
Note: The problem with using a dictionary alone as a backing for your picker is that the order is not specified explicitly. Adding or removing keys may change the order of existing keys. In addition, existing keys may not end up in places that you want them to be - for example, your "" - "not specified" pair may end up in the middle of the picker.
To fix this problem, keep a separate array of city keys in the proper order that you wish to follow. Use this array to decide the picker row in which a city is to be displayed, and look up the actual city using the dictionary.

Answer 2

You can use NSUserDefaults to insure the persistency of your cityCode.
Copy an paste this sample in a playground.
var cities: [String: String] = ["":"not specified", "ny":"New York", "la":"Los Angeles", "sf":"San Francisco"]
let cityCodeIndexKey="cityCodeIndexKey"
/**
Selects and saves the cityCode
- parameter cityCode: a cityCode String
- returns: true if the code exists.
*/
func selectCity(cityCode:String)->Bool{
if let _ = cities.indexForKey(cityCode){
NSUserDefaults.standardUserDefaults().setObject(cityCode, forKey:cityCodeIndexKey)
NSUserDefaults.standardUserDefaults().synchronize()
return true
}else{
return false
}
}
selectCity("ny") // Returns true
selectCity("pr") // Returns false
NSUserDefaults.standardUserDefaults().valueForKey(cityCodeIndexKey) // returns "ny"

Answer 3

Get key,
var cityLongName <- user selected one
var key = dict.first((key,value) In{
If (value == cityLongName ){
return true
}else{
return false
}
}).key!
Get values ,
var value = dict[“city sort name”]