I have an array of dictionaries inside a dictionary. I initialize it like this:
var fillups:[NSMutableDictionary] = []
Then I load it like this:
fillups = userDefaults.object(forKey: car) as! NSArray as! [NSMutableDictionary]
Then when I try to update a dictionary element in the array I get the "mutating method sent to immutable object" error. Here's my code to update the record:
let dict=fillups[row]
dict.setValue(odometerField.text, forKey: "odometer")
dict.setValue(gallonsField.text, forKey: "gallons")
fillups[row]=dict
The error occurs in my first setValue line.
Objects that you retrieve from NSUserDefaults are immutable even if they were mutable when they were inserted. You need to take the immutable objects you get from defaults and create mutable versions of them. You also shouldn't force unwrap everywhere if you don't want your app to crash.
if let array = userDefaults.object(forKey: car) as? [NSDictionary] {
fillups = array.map { ($0.mutableCopy() as! NSMutableDictionary) }
}
You also don't need the fillips[row] = dict line since NSMutableDictionary is a reference type and editing the reference you pull out of the array is already editing the one inside the array.
If you want to mutate your dict, you need to declare it with 'var' not with 'let'; 'let' is for constants. Also fix the unwrapping problems pointed out by the comment
let dict=fillups[row]
should be
var dict=fillups[row]
Related
I have an dictionary and the value containts the array of string as follows
arr = ["key":"["a","b","c","d","e","f","g"]"]
I want the new array to be like
let array = ["a","b","c","d","e","f","g"]
How to parse it
You can access dictionary items in few different ways, the easiest is:
let array = arr["key"]
You may need to conditionally unwrap it
if let array = arr["key"] as? [String] {
// rest of code with array
}
I have a json.I am trying to parse that with that code.But its says
Could not cast value of type '__NSArrayM' to 'NSDictionary'
do {
let dataDictionary: NSDictionary = try NSJSONSerialization.JSONObjectWithData(responseObject as! NSData, options: NSJSONReadingOptions.MutableContainers) as! NSDictionary // <------ Error
if let customerArray = dataDictionary.valueForKey("cart") as? NSArray {
for js in customerArray {
let nameArray = js.valueForKey("name")
let idArray = js.valueForKey("id")
}
}
}
Thank you for your helps
The root object in your data is an array, not a object (dictionary).
You need to dynamically decide how to handle your JSON depending on the deserialized object.
What it's telling you is that the JSON object that you're parsing is not a dictionary, it's an array. So if you change it so that you treat its value as an array instead of a dictionary, you'll be able to iterate over that.
You need to reevaluate your JSON to ensure that it's structured the way you think it is. It would also be useful if you posted the JSON that you're trying to parse so that we can see it's structure as well.
I have put an array into NSUserDefaults() like so:
NSUserDefaults.standardUserDefaults().setObject(users, forKey: "usersArray")
NSUserDefaults.standardUserDefaults().synchronize()
Then I pull it out like so:
fetchedUserArray = NSUserDefaults.standardUserDefaults().objectForKey("usersArray")
The problem I am facing is that once it is removed from NSUserDefaults it is of type NSArray, preventing me from manipulating it like a Swift array. I have tried this to convert the type, however the compiler does not recognize the variable "castedUsersArray" when it is used later in the code despite not raising any errors upon type casting:
var fetchedArray = NSUserDefaults.standardUserDefaults().objectForKey("usersArray") as? NSArray
var castedUsersArray = fetchedArray as AnyObject as [String]
I have spent a very long time on this with no success. The type constraints of Swift are driving me nuts.
Thank you,
Nick
You almost had it. Don't cast the objectForKey to an Array but rather an Array containing a certain type like you did with castedUsersArray. Don't throw away type information like you did with fetchedArray.
let users = ["Amy", "Bill", "Cindy"]
NSUserDefaults.standardUserDefaults().setObject(users, forKey: "usersArray")
NSUserDefaults.standardUserDefaults().synchronize()
let fetched = NSUserDefaults.standardUserDefaults().objectForKey("usersArray") as? [String] ?? []
The nil coalescing at the end of the line handles the empty NSUserDefaults case.
NSUserDefaults has a specific method to get your stored string arrays called stringArrayForKey:
let stringArray = ["Hello","playground"]
store your string array
NSUserDefaults.standardUserDefaults().setObject(stringArray, forKey: "stringArray")
load it when needed
if let loadedStringArray = NSUserDefaults.standardUserDefaults().stringArrayForKey("stringArray") {
print(loadedStringArray) // ["Hello", "playground"]
}
In the Swift PDF file released by Apple i came thorough this code
To create an empty array or dictionary, use the initializer syntax.
let emptyArray = [String]()
let emptyDictionary = [String: Float]()
Here what is the use of creating a let (constant) object with empty array, where we cannot insert any values into it in next line ??!!
while teaching objective- c they start teaching like
NSArray *arrayObj = [[NSArray alloc] init]
if we declare like this we cannot add objects after initialisation
similarly they are teaching us how to initialise an array or dictionary objects
one more difference is if we allocate an empty array then we can assign another array with this.
let will not allow you to assign another array to it also
let emptyArray = [String]()
let/var filledArray = ["stack", "overflow"]
emptyArray = filledArray // will give you an error
Not much use, but the value can be copied:
let emptyDictionary = [String: Float]()
var otherDictionary = emptyDictionary
otherDictionary["a"] = 0.5
The property declaration sets them to a default, but you could actually change the value to something else in init. This would only be the case for class properties, not inline properties though.
Here's an example in a class scope where a let property can have a default but be changed:
class Whatever {
let testArray = [Int]()
init() {
testArray = [0,1,2]
}
}
I am having a devil of a time trying to work with Dictionaries in Swift. I have created the following Dictionary of Dictionaries but I am unable to unpack it.
var holeDictionary = Dictionary<String,Dictionary<String,Dictionary<String,Int>>>()
I can get the first Dictionary out with:
var aDictionary = holeDictionary["1"]
But trying to access the next Dictionary within it gives me an error as follows:
var bDictionary = aDictionary["key"] // [String : Dictionary<String, Int>]?' does not have a member named 'subscript'
I know what the contents of the Dictionaries are and can verify them with a println(aDictionary). So how can I get to the Dictionaries buried deeper down?
The key subscript on Dictionary returns an optional, because the key-value pair may or may not exist in the dictionary.
You need to use an if-let binding or force unwrap the optional before you can access it to subscript it further:
if let aDictionary = holeDictionary["1"] {
let bDictionary = aDictionary["key"]
}
Edit, to add forced unwrap example:
If you're sure that the key "1" exists, and you're okay with assert()ing at runtime if the key doesn't exist, you can force-unwrap the optional like this:
let bDictionary = holeDictionary["1"]!["key"]
And if you're sure that the key "key" will exist, you'd do this instead:
let bDictionary = holeDictionary["1"]!["key"]!
Accordingly to the swift documentation:
Because it is possible to request a key for which no value exists,
a dictionary’s subscript returns an optional value of the dictionary’s
value type
When you retrieve an item from a dictionary you have an optional value returned. The correct way to handle your case is:
var holeDictionary = Dictionary<String,Dictionary<String,Dictionary<String,Int>>>()
if let aDictionary = holeDictionary["1"] {
var bDictionary = aDictionary["key"]
}