I'm trying to save a dictionary to NSUserDefaults using the setObject() function but when I use the objectForKey() function to retrieve the dictionary it returns nil. Why is this happening?
var data = NSUserDefaults.standardUserDefaults();
var scoreboard = [Int : String]()
let scores = "scoresKey"
scoreboard[3] = "spencer"
scoreboard[6] = "brooke"
scoreboard[11] = "jason"
data.setObject(scoreboard, forKey: scores)
data.objectForKey(scores) // Returns nil
The first problem was that it's not possible to use NSUserDefaults in a Playground.
See: https://stackoverflow.com/a/31210205/3498950
A second problem is found when the code above runs in a normal iOS project. It throws an NSInvalidArgumentException since the dictionary was a non-property list object because the keys needed to be of type String.
Although NSDictionary and CFDictionary objects allow their keys to be
objects of any type, if the keys are not string objects, the
collections are not property-list objects.
See: "What is a Property List?" in the Apple Docs
Related
Is this proper syntax for this line of code? If not what would be the correct syntax and why so?
UserDefaults.standard.dictionary(forKey: "mainDict")?.updateValue(subDict, forKey: "subDictTitle")
First, you have to store Userdefault dictionary to a temporary dictionary. Then you have to add data to a temporary dictionary.
No need to update the dictionary to Userdefault. When you store Dictionary to the Usedefault with the same key, it will replace the older dictionary to the new one.
UserDefaults.standard.set(YOUR_TEMPORARY_DICTIONARY, forKey: YOUR_KEY_NAME)
The updateValue(_:forKey:) is a mutating instance method for the dictionary, which means that it updates the value of the dictionary. Obviously, In order to mutate an instance, it has to be mutable, which is not the case when calling UserDefaults.standard.dictionary(forKey: "mainDict").
Even if you did:
let myDict = ["k1": "Hello"]
UserDefaults.standard.register(defaults: ["myDict": myDict])
var mutable = UserDefaults.standard.dictionary(forKey: "myDict")!
mutable["k1"] = "HEY"
print(UserDefaults.standard.dictionary(forKey: "myDict")) // Optional(["k1": Hello])
the value of the dictionary set in the user default won't change because simply mutable is a copy of it.
To clarify, it's similar to implementing:
UserDefaults.standard.register(defaults: ["k2": "this is my string"])
UserDefaults.standard.string(forKey: "k2") = "new string"
which generates the error of
Expression is not assignable: function call returns immutable value
So, in order to resolve this issue, what you should do is to set a new value (updated dictionary) to the user defaults with the same key:
var myDict = UserDefaults.standard.dictionary(forKey: "myDict")
myDict?.updateValue("Hey", forKey: "k1")
UserDefaults.standard.set(myDict, forKey: "myDict")
NSArray.init(array: [Any])
NSArray has an initial function whose parameter is [Any]. But not [Any?], so, how to add a nil value to this array?
NSArray/NSMutableArray don't allow you to store nil values in the array. This is why none of the Swift APIs allow optional values.
If you really need to something for nil, use NSNull() though I'm not 100% sure how that will work with Core Data.
And Swift actually does this for you. If you pass a Swift array of optionals, any nil values get converted to NSNull. Example:
var array = [Int?]()
array.append(4)
array.append(nil)
let nsa = array as NSArray
print(nsa) // (4, "<null>")
print(type(of: nsa[1])) // NSNull
Note that using let nsa = NSArray(array: array) instead of let nsa = array as NSArray worked without warning under Swift 4.0 but gives a warning as of Swift 4.1.
I have a variable set of objects that I need to place in a dictionary. I'm trying to add them to the dictionary in a for loop but from what I'm understanding dictionaries are immutable so they need to be declared immediately. How do I create a dictionary list of items that are not predetermined?
var newItems = [:]
for item in self.items{
newItems["\(item.key)"]["name"] = "A new item"
}
does not use the second value
var newItems : [String:String] = [:]
for i in 1..10{
newItems[i.description] = "A new item"
}
for more information https://www.weheartswift.com/dictionaries/
The problem with your original code is that dictionaries only have one key, so this construct newItems["\(item.key)"]["name"] is syntactically incorrect. If you had a fixed number of properties you could use a struct and put that in a dictionary. As you posed the question, though, you need to create a dictionary where the stored elements themselves are dictionaries. So, although I didn't actually put this into Xcode, it's a template for what you need to do:
var newItems = [:[:]]()
for item in self.items {
var itemDict = [:]()
for prop in whereeveryourpropertiescomefrom {
itemDict[prop] = valueforthisproperty
}
newItems["\(item.key)"] = itemDict
}
Of course, if your properties were initially stored in a dictionary unique to this item (equivalent of the inner loop), just store it directly into newItems.
Then, you could reference things as
let value = newItems["\(item.key)"]?.["property key"]
Notice the dictionary retrieval returns an optional you have to deal with.
The solution was when initializing the dictionary to create another dictionary
var newItems: [String:[String:AnyObject]]()
I've a mutable dictionary (in form of [Int:Int]) and want that to save it. I would use NSUserDefaults like that:
var myDic: NSMutableDictionary = [:]
myDic = [1:2]
NSUserDefaults.standardUserDefaults().setObject(myDic, forKey: "myDic")
but with that I get an error:
Thread 1: signal SIGABRT
I have no idea why.
setObject(_:forKey:) can’t accept Dictionary with a key which is integer type. The method requires property-list objects, but myDic = [1:2] is not property-list object.
There are two documents about it.
setObject(_:forKey:) of NSUserDefaults
The value parameter can be only property list objects: NSData,
NSString, NSNumber, NSDate, NSArray, or NSDictionary. For
NSArray and NSDictionary objects, their contents must be property
list objects.
About Property Lists
And although NSDictionary and CFDictionary objects allow their keys to
be objects of any type, if the keys are not string objects, the
collections are not property-list objects.
If you set a integer-key to Dictionary, the Dictionary object cannot be used for a value of setObject. You have to use a string for the key like this:
myDic = ["1": 2]
I have been porting some objective-c code over into swift and I am trying to get the result set as a dictionary and then pack each dictionary (equivalent to a row from the db) into an array. But I am getting this error message "Dictionary cannot be bridged from Objective-C". I have read this from apple but still I am no further along towards a solution. Any ideas? Thanks.
This is the line where the error is:
resultsArray.append(resultSet!.resultDictionary() as Dictionary<String,String>)
From the awesome robertmryan reposted here for convenience:
This will happen if your database has an null values (which return [NSNull null] objects) or numeric values (which return NSNumber objects). You can fix this by defining resultsArray as:
var resultsArray = Array<Dictionary<String,AnyObject>>()
Or, I personally prefer:
var resultsArray = [[String: AnyObject]]()
And then when adding objects, I'd
resultsArray.append(resultSet!.resultDictionary() as Dictionary<String, AnyObject>)
or
resultsArray.append(resultSet!.resultDictionary() as [String: AnyObject])