ios Swift：声明一个空字典

Swift: declare an empty dictionary

提问by z22

I am beginning to learn swiftby following the iBook-The Swift Programming Languageon Swift provided by Apple. The book says to create an empty dictionary one should use [:]same as while declaring array as []:

我开始学习Apple 提供swift的 iBook- The Swift Programming Languageon Swift。这本书说要创建一个空字典，应该使用[:]与将数组声明为相同的方法[]：

I declared an empty array as follows :

我声明了一个空数组，如下所示：

let emptyArr = [] // or String[]()

But on declaring empty dictionary, I get syntax error:

但是在声明空字典时，我收到语法错误：

let emptyDict = [:]

How do I declare an empty dictionary?

如何声明一个空字典？

回答by damirstuhec

var emptyDictionary = [String: String]()

­

­

var populatedDictionary = ["key1": "value1", "key2": "value2"]

Note: if you are going to change the contents of the dictionary over time then declare it as a var(variable). You candeclare an empty dictionary as a let(constant) but it is pointless if you have the intention of changing its contents over time, since constant can't be changed after it has been initialized.

注意：如果您打算随时间更改字典的内容，请将其声明为var（变量）。您可以将空字典声明为let（常量），但如果您打算随时间更改其内容，则毫无意义，因为常量在初始化后无法更改。

---

---

Old answer:

旧答案：

Creating an empty dictionary of type <String, String>would look as follows:

创建类型为空的字典<String, String>如下所示：

var emptyDictionary = Dictionary<String, String>()

回答by Gabriele Petronella

You can't use [:]unless type information is available.

[:]除非类型信息可用，否则您不能使用。

You need to provide it explicitly in this case:

在这种情况下，您需要明确提供它：

var dict = Dictionary<String, String>()

varmeans it's mutable, so you can add entries to it. Conversely, if you make it a letthen you cannot further modify it (letmeans constant).

var意味着它是可变的，所以你可以向它添加条目。相反，如果您将其设为 a，let则无法进一步修改它（let表示常量）。

You can use the [:]shorthand notation if the type information can be inferred, for instance

[:]例如，如果可以推断类型信息，则可以使用速记符号

var dict = ["key": "value"]

// stuff

dict = [:] // ok, I'm done with it

In the last example the dictionary is known to have a type Dictionary<String, String>by the first line. Note that you didn't have to specify it explicitly, but it has been inferred.

在最后一个例子中Dictionary<String, String>，第一行就知道字典有一个类型。请注意，您不必明确指定它，但它已被推断出来。

回答by Suragch

The Swift documentationrecommends the following way to initialize an empty Dictionary:

在斯威夫特文档建议采取以下方法来初始化一个空字典：

var emptyDict = [String: String]()

I was a little confused when I first came across this question because different answers showed different ways to initialize an empty Dictionary. It turns out that there are actually a lot of ways you can do it, though some are a little redundant or overly verbose given Swift's ability to infer the type.

当我第一次遇到这个问题时，我有点困惑，因为不同的答案显示了初始化空字典的不同方法。事实证明，实际上有很多方法可以做到，尽管鉴于 Swift 推断类型的能力，有些方法有点多余或过于冗长。

var emptyDict = [String: String]()
var emptyDict = Dictionary<String, String>()
var emptyDict: [String: String] = [:]
var emptyDict: [String: String] = [String: String]()
var emptyDict: [String: String] = Dictionary<String, String>()
var emptyDict: Dictionary = [String: String]()
var emptyDict: Dictionary = Dictionary<String, String>()
var emptyDict: Dictionary<String, String> = [:]
var emptyDict: Dictionary<String, String> = [String: String]()
var emptyDict: Dictionary<String, String> = Dictionary<String, String>()

After you have an empty Dictionary you can add a key-value pair like this:

在你有一个空的 Dictionary 之后，你可以像这样添加一个键值对：

emptyDict["some key"] = "some value"

If you want to empty your dictionary again, you can do the following:

如果要再次清空字典，可以执行以下操作：

emptyDict = [:]

The types are still <String, String>because that is how it was initialized.

类型仍然<String, String>是因为它是如何初始化的。

回答by Lim Thye Chean

Use this will work.

使用这个会起作用。

var emptyDict = [String: String]()

回答by Jio

You can simply declare it like this:

你可以简单地像这样声明它：

var emptyDict:NSMutableDictionary = [:]

回答by nevan king

You have to give the dictionary a type

你必须给字典一个类型

// empty dict with Ints as keys and Strings as values
var namesOfIntegers = Dictionary<Int, String>()

If the compiler can infer the type, you can use the shorter syntax

如果编译器可以推断类型，则可以使用较短的语法

namesOfIntegers[16] = "sixteen"
// namesOfIntegers now contains 1 key-value pair
namesOfIntegers = [:]
// namesOfIntegers is once again an empty dictionary of type Int, String

回答by Juan Boero

Swift:

迅速：

var myDictionary = Dictionary<String, AnyObject>()

回答by Lorem Ipsum Dolor

You need to explicitly tell the data type or the type can be inferred when you declare anything in Swift.

当你在 Swift 中声明任何东西时，你需要明确地告诉数据类型或者类型可以被推断出来。

Swift 3

斯威夫特 3

The sample below declare a dictionary with key as a Inttype and the value as a Stringtype.

下面的示例声明了一个字典，键是Int类型，值是String类型。

Method 1: Initializer

方法一：初始化器

let dic = Dictionary<Int, String>()

Method 2: Shorthand Syntax

方法 2：速记语法

let dic = [Int:String]()

Method 3: Dictionary Literal

方法 3：字典字面量

var dic = [1: "Sample"]
// dic has NOT to be a constant
dic.removeAll()

回答by Shakeel Ahmed

Swift 4

斯威夫特 4

let dicc = NSDictionary()

//MARK: - This is empty dictionary
let dic = ["":""]

//MARK:- This is variable dic means if you want to put variable 
let dic2 = ["":"", "":"", "":""]

//MARK:- Variable example
let dic3 = ["name":"Shakeel Ahmed", "imageurl":"https://abc?abc.abc/etc", "address":"Rawalpindi Pakistan"]

//MARK: - This is 2nd Variable Example dictionary
let dic4 = ["name": variablename, "city": variablecity, "zip": variablezip]

//MARK:- Dictionary String with Any Object
var dic5a = [String: String]()
//MARK:- Put values in dic
var dic5a = ["key1": "value", "key2":"value2", "key3":"value3"]

var dic5b = [String:AnyObject]()
dic5b = ["name": fullname, "imageurl": imgurl, "language": imgurl] as [String : AnyObject]

or
//MARK:- Dictionary String with Any Object
let dic5 = ["name": fullname, "imageurl": imgurl, "language": imgurl] as [String : AnyObject]

//MARK:- More Easy Way
let dic6a = NSDictionary()
let dic6b = NSMutalbeDictionary()

回答by Lee Probert

I'm playing with this too. It seems strange that you can just declare an empty dictionary and then add a key/value pair to it like so :

我也在玩这个。你可以声明一个空字典，然后像这样添加一个键/值对，这似乎很奇怪：

var emptyDictionary = Dictionary<String, Float>()
var flexDictionary = [:]
emptyDictionary["brian"] = 4.5
flexDictionary["key"] = "value" // ERROR : cannot assign to the result of this expression

But you can create a Dictionary that accepts different value types by using the "Any" type like so :

但是您可以使用“Any”类型创建一个接受不同值类型的字典，如下所示：

var emptyDictionary = Dictionary<String, Any>()
emptyDictionary["brian"] = 4.5
emptyDictionary["mike"] = "hello"