What is the right way to cast Dictionary in Swift 3 to a CFDictionary? Is it legal to write like this?
var dictionary:Dictionary<NSString, Int> = [:]
and then
dictionary as CFDictionary
Yes you can do that. your solution will work and you can also do it like this.
var dictionary = [
key:value
] as CFDictionary
You can refer further from here
Related
I have a dictionary, something like this
var dict = [String : [String]]()
The functionality I want to achieve is that, I have a hashtable which I can quick get the list of data from.
In my code, I use a dictionary and an array.
I am not very good with algorithem and data structure, so I am wondering if there is any better data structure that is suitable for something like this?
Use:
var dict = [String : [String]]()
Swift already has built in search algorithms that allow you you to retrieve data inside of your dictionary with simple subscript syntax like so
dict["element"]
You will use it in this way -
Declaration:
var dict: [String: [String]] = [:]
Initialise:
dict["element"] = myArray
I need to read and write some data from CFDictionary instances (to read and update EXIF data in photos). For the life of me, I cannot figure out how to do this in Swift 3. The signature for the call I want is:
func CFDictionaryGetValue(CFDictionary!, UnsafeRawPointer!)
How the heck do I convert my key (a string) to an UnsafeRawPointer so I can pass it to this call?
If you don't have to deal with other Core Foundation functions expecting an CFDictionary, you can simplify it by converting to Swift native Dictionary:
if let dict = cfDict as? [String: AnyObject] {
print(dict["key"])
}
Be careful converting a CFDictionary to a Swift native dictionary. The bridging is actually quite expensive as I just found out in my own code (yay for profiling!), so if it's being called quite a lot (as it was for me) this can become a big issue.
Remember that CFDictionary is toll-free bridged with NSDictionary. So, the fastest thing you can do looks more like this:
let cfDictionary: CFDictionary = <code that returns CFDictionary>
if let someValue = (cfDictionary as NSDictionary)["some key"] as? TargetType {
// do stuff with someValue
}
What about something like:
var key = "myKey"
let value = withUnsafePointer(to: &key){ upKey in
return CFDictionaryGetValue(myCFDictionary, upKey)
}
You can write something like this:
let key = "some key" as NSString
if let rawResult = CFDictionaryGetValue(cfDictionary, Unmanaged.passUnretained(key).toOpaque()) {
let result = Unmanaged<AnyObject>.fromOpaque(rawResult).takeUnretainedValue()
print(result)
}
But I guess you would not like to write such thing at any time you retrieve some data from that CFDictionary. You better convert it to Swift Dictionary as suggested in Code Different's answer.
I was having trouble storing a Dictionary in the NSUserDefaults, and then I had trouble retrieving the values. After a failed search on the web, I finally figured it out and so I hope this helps you with this same issue.
Define your variables for NSUserDefaults, Dictionary and key:
let defaults = NSUserDefaults.standardUserDefaults()
var myDictionary = Dictionary<String, Int>()
let myKey = "Key"
How to save your dictionary:
defaults.setObject(myDictionary, forKey: myKey)
How to retrieve your dictionary:
myDictionary = defaults.dictionaryForKey(myKey) as! Dictionary<String, Int>
NOTE: make sure that your data types are the same as the way you set them up.
*** FYI, this is using Xcode 6.3.2
Hello Everyone I am new in swift and In my app I declare a dictionary like this :
var imageDict : Dictionary<String, String> = [:]
and I want to set values for that dictionary like this :
imageDict.setValue(NSStringFromCGPoint(frame), forKey: NSString.stringWithString("/(tagValue)"));
But I got error like this :
Dictonary <String, String> does not have a member named 'setValue'
This question is from my previous question and can enybody explain my why I can not set value for that dictionar and can enybody tell me any other way to do that?
Thanks In advance.
Swift dictionary does not have method like setValue:forKey:. Only NSMutableDictionary has such methods. If you wish to assign value for key in swift, you should use subscripting. Here is the correct way to do it, if you wish to do it with swift dictionary.
var imageDict:[String: String] = [:]
imageDict["\(tagValue)"] = NSStringFromCGRect(frame)
Or if you wish to use NSMutableDictionary then, it looks like this,
var imageDict = NSMutableDictionary()
imageDict.setObject(NSStringFromCGRect(frame), forKey: "\(tagValue)")
I guess you need to use NSMutableDictionary.
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
]