func exercise() {
var stockTickers: [String: String] = [
"APPL" : "Apple Inc",
"HOG": "Harley-Davidson Inc",
"BOOM": "Dynamic Materials",
"HEINY": "Heineken",
"BEN": "Franklin Resources Inc"
]
stockTickers["WORK"] = ["Slack Technologies Inc"]
stockTickers["BOOM"] = ["DMC Global Inc"]
print(stockTickers["WORK"]!)
print(stockTickers["BOOM"]!)
}
Error: Cannot assign value of type '[String]' to subscript of type 'String'
I do not understand the error, I'm new to swift, can someone guide me through this and tell mw why I see this error.
Alexander explained what you need to do in abstract terms. (Voted)
Specifically, change
stockTickers["WORK"] = ["Slack Technologies Inc"]
stockTickers["BOOM"] = ["DMC Global Inc"]
To
stockTickers["WORK"] = "Slack Technologies Inc"
stockTickers["BOOM"] = "DMC Global Inc"
The expression ["Slack Technologies Inc"] defines a String array containing a single string. That's not what you want. you defined a dictionary of type [String:String]
If you wanted your dictionary to have String keys and values that contained arrays of strings, you'd have to change the way you declared your dictionary:
var stockTickers: [String: [String]] = [
"APPL" : ["Apple Inc"],
"HOG": ["Harley-Davidson Inc"],
"BOOM": ["Dynamic Materials"],
"HEINY": ["Heineken"],
"BEN": ["Franklin Resources Inc"]
]
["DMC Global Inc"] is an array literal containing a string. It evaluates to a value of type [String] (a.k.a. Array<String>).
Thus the error makes sense: you’re trying to a assign an array of strings in a place where only a String is expected.
Just remove the square brackets.
Related
I'm really new to swift and spent whole day trying to parse simple json, received thought websockets. Finally I got parsed (kinda), but many things still lay way beyond my understanding and I ask for some explanation.
Ok, here is what I have got so far
First of all I declare variable QUOTES, which will be Dictionary, same as in json
var QUOTES: Dictionary<String, Dictionary<String, Any>>
I want my QUOTES var look like this at the end:
{
"AAPL": {name: "Apple Comp", "price": 100},
"F": {name: "Ford Comp", "price": 200}
}
When my websocket receives data, I want to populate QUOTES with received data.
socket.on("q"){data, ack in
//data looks like this: [{q:[{c: "AAPL", price: 100}, {c: "F", price: 100}]}]
//I convert first element of received [Any] to dictionary
let object = data[0] as! Dictionary<String, NSArray>
//I get array of quotes out of received data
let quotes = object["q"] as! [Dictionary<String, Any>]
//Now I want to iterate through received quotes to fill me QUOTES variable declared in the very beginning
for quote in quotes {
//I know ticker of current quote
let ticker = quote["c"] as! String
//Not sure if I have to do it - if QUOTES does not have current ticker in dictionary, I create it as empty dictionary
if (QUOTES[ticker] == nil) {
QUOTES[ticker] = [String: Any]()
}
//Now I iterate properties of received quote
for(k,v) in quote {
//And I want to fill my QUOTES dictionary,
// but I get compile error
//Value of optional type '[String : Any]?' not unwrapped; did you mean to use '!' or '?'?
//I don't understand what compiler wants me to do?
QUOTES[ticker][k] = v
}
}
}
but I get compile error
Value of optional type '[String : Any]?' not unwrapped; did you mean to use '!' or '?'?
I don't understand what compiler wants me to do?
For the following variable
var dict2 = ["key1" : "value1", "key2" : [ "value1" , "value2" ]]
How to add a third value for the second key of the following dictionary?
If I can reformulate your dict2 declaration slightly:
var dict2 = ["key1" : ["value1"], "key2" : [ "value1" , "value2" ]]
then you can append an extra item to key2 like this:
dict2["key2"]?.append("value3")
However, you will probably need to be careful to check that key2 was already present. Otherwise, the above statement will do nothing. In which case you can write:
if dict2["key2"]?.append("value3") == nil {
dict2["key2"] = ["value3"]
}
Why did I change the original declaration? With the version I gave, dict2 will be of type [String:[String]]. But with your version, what Swift is doing is declaring a much more loosely typed [String:NSObject]. This compiles, but behaves very differently (contents will have reference not value semantics, you will have to do type checks and casts frequently etc), and is probably best avoided.
#AirspeedVelocity provides a working solution, but requiring a small change to the way the data is defined - but that is what I would do myself, if possible.
However if you have to stick with the original data format, you can use this code:
var dict2: [String : AnyObject] = ["key1" : "value1", "key2" : [ "value1" , "value2" ]]
var array = dict2["key2"] as? [String]
array?.append("value3")
dict2["key2"] = array
First we make explicit the dict2 type, a dictionary using strings as keys and AnyObject as values.
Next we extract the value for the key2 key, and attempt to cast to an array of strings - note that this returns an optional, so the type of array is [String]?
In the next line we add a new element to the array - note that if array is nil, the optional chaining expression evaluates to nil, and nothing happens
In the last line, we set the new array value back to the corresponding key - this step is required because the array is a value type, so when we extract it from the dictionary, we actually get a copy of it - so any update made on it won't be applied to the original array.
I've been through similar questions but still do not understand why my code is throwing an error.
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
dict["participants"][0] = "baz"
The error is on line 3: (String: AnyObject) does not have a member named 'subscript'
I'm setting the participants key to an array and then trying to update the first element of it without any luck. The code above is shortened for example purposes, but I am using [String:AnyObject] because it is not only arrays that are stored in the dictionary.
It's probably something really trivial but I am still new to Swift. Thanks for any help in advance!
The error message tells you exactly what the problem is. Your dictionary values are typed as AnyObject. I know you know that this value is a string array, but Swift does not know that; it knows only what you told it, that this is an AnyObject. But AnyObject can't be subscripted (in fact, you can't do much with it at all). If you want to use subscripting, you need to tell Swift that this is not an AnyObject but rather an Array of some sort (here, an array of String).
There is then a second problem, which is that dict["participants"] is not in fact even an AnyObject - it is an Optional wrapping an AnyObject. So you will have to unwrap it and cast it in order to subscript it.
There is then a third problem, which is that you can't mutate an array value inside a dictionary in place. You will have to extract the value, mutate it, and then replace it.
So, your entire code will look like this:
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
var arr = dict["participants"] as [String] // unwrap the optional and cast
arr[0] = "baz" // now we can subscript!
dict["participants"] = arr // but now we have to write back into the dict
Extra for experts: If you want to be disgustingly cool and Swifty (and who doesn't??), you can perform the mutation and the assignment in one move by using a define-and-call anonymous function, like this:
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
dict["participants"] = {
var arr = dict["participants"] as [String]
arr[0] = "baz"
return arr
}()
I have the following swift dictionary
var List = [
2543 : [ "book", "pen" ],
2876 : [ "school", "house"]
]
How can i access the array values ?
println(List[2543][0])
The above code gives error "could not find member subscript"
and it should print "book"
Note that subscript returns an optional. We have to force unwrapping:
println(list[2543]![0])
Or use optional chaining
println(list[2543]?[0])
println(list[2543]![0])
Remember, dictionary subscript returns an Optional, not an array or whatever is inside the dictionary value.
Just try with following code:
var dic = List[0];
println("values \(dic)")
OR
println(list[2543]![0])
Swift only allows a dictionary to contain a single type.
Here's the definition that is taken from the Swift book:
A dictionary is a container that stores multiple values of the same type
[...]
They differ from Objective-C’s NSDictionary and NSMutableDictionary classes, which can use any kind of object as their keys and values and do not provide any information about the nature of these objects.
If that’s the case then how are we going to create nested dictionaries?
Imagine we have a plist that holds String, Array and Dictionary items in it . If I’m allowed to hold only the same of type of items (either string, array etc.) then how am I going to use different types of items stored in the plist?
How do I put different types in the same dictionary in Swift?
You can achieve plist-like nested structures using Any type for dictionary values which is Swift's somewhat counterpart to Objective-C's id type but can also hold value types.
var response = Dictionary<String, Any>()
response["user"] = ["Login": "Power Ranger", "Password": "Mighty Morfin'"]
response["status"] = 200
EDIT:
Any seems to be better than AnyObject because in the above code response["status"] is of type Swift.Int, while using value type of AnyObject it is __NSCFNumber.
As has been suggested, you can use the Any type to represent a plist dictionary's values. But then how do you work with the data? Cast every value any time you look it up from the dictionary? That's really messy. A better, more type-safe way to model a plist would be to take advantage of Swift's enums, also known as algebraic data types or discriminated unions. They let you specify exactly what types are permitted in the dictionary and avoid ever having to cast. Here's an implementation, explained:
// An atomic (i.e. non-collection) data type in a plist.
enum PListNode {
case PLN_String(String)
case PLN_Integer(Int)
case PLN_Float(Double)
case PLN_Bool(Bool)
case PLN_Date(CFDate)
case PLN_Data(CFData)
}
At the most atomic level, only the above data types may be stored in a plist. Each 'node' in the plist can ultimately can only be one of these types. So we create an enum which lets us specify this.
// A value that can be stored in a plist Dictionary's key-value pair.
enum PListValue {
case PLV_Node(PListNode)
case PLV_Array(PListNode[])
case PLV_Dictionary(Dictionary<String, Box<PListValue>>)
}
typealias PList = Dictionary<String, Box<PListValue>>
A plist is basically a dictionary of key-value pairs, and each value can be either an atomic (i.e. non-collection) value; or it can be an array of atomic values; or it can be a dictionary of string-plist value pairs. The above enum expresses these constraints, and the typealias gives the plist type an easy-to-remember name.
Given the above types, we can completely express any given plist in a type-safe way, e.g.:
// Example translated from
// https://developer.apple.com/library/Mac/documentation/Darwin/Reference/ManPages/man5/plist.5.html
let myPlist: PList = [
"Year Of Birth": Box(PLV_Node(PLN_Integer(1965)))
, "Pets Names": Box(PLV_Array([]))
, "Picture": Box(PLV_Node(PLN_Data(...)))
, "City of Birth": Box(PLV_Node(PLN_String("Springfield")))
, "Name": Box(PLV_Node(PLN_String("John Doe")))
, "Kids Names": Box(
PLV_Array([PLN_String("John"), PLN_String("Kyra")])
)
]
What it means to be type-safe here is that you can process any given plist using a switch statement and cover all possibilities without the need for any casting. You're eliminating a whole class of potential runtime errors. E.g.:
// See https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Enumerations.html#//apple_ref/doc/uid/TP40014097-CH12-XID_189 for explanation
switch myPlist["Year Of Birth"] {
case Box(.PLV_Node(let plvNodeValue)):
...
case Box(.PLV_Array(let plvArrayValue)):
...
case Box(.PLV_Dictionary(let plvDictionaryValue)):
...
}
Note that it's necessary to wrap up recursive data structures in a 'box' (a pointer to the actual value) to keep their sizes finite.
NSObject works for my case while "Any" does not
var d:Dictionary<String,NSObject> = [:]
d["key1"] = "ddd"
d["key2"] = 111 //OK
NSLog("%#", d) //OK
var d2:Dictionary = Dictionary<String,Any>()
d2["key1"] = "ddd"
d2["key2"] = 111
NSLog("%#", d2) //I got error here
Use NSMutableDictionary like this :
var dictInfo : NSMutableDictionary = [ "lang_key": "1"]
dictInfo["food_type"] = lbl_TypeOfFood.text
dictInfo["search_text"] = txt_Search.text
dictInfo["date"] = lbl_Date.text
dictInfo["opening_hours"] = lbl_OpeningHours.text
hope this will work fine .
Use: Dictionary<String, AnyObject>
var dict: Dictionary<String, AnyObject> = [
"number": 1,
"string": "Hello",
]
NSMutableDictionary to Dictionary works like a charm and will allow you to put different types in a Dictionary in the Swift Language:
let nsMutableDictionary = NSMutableDictionary()
nsMutableDictionary[NSFontAttributeName] = UIFont(name: "HelveticaNeue", size: 12.0)!
nsMutableDictionary[NSForegroundColorAttributeName] = UIColor.redColor()
let dictionary: Dictionary<NSObject, AnyObject> = nsMutableDictionary
self.attributedPlaceholder = NSAttributedString(string: textParam, attributes: dictionary)
let dictionary : Dictionary = [
"key": "value",
"key2": 2,
"key3": NSString(),
2: "test",
]
One can specify types which restricts the dictionary
let dictionary : Dictionary<String, String> = [
"key": "value",
"key2": 2, // This errors
]