斯威夫特词典 [英] Dictionary in Swift

问题描述

我真的很混淆我们在swift中创建字典的方式。那么可以请你告诉我有什么不同之处吗？

  var myDic3 = [String：AnyObject]（）
  

和

  var myDic2 = Dictionary< Int，AnyObject>（）
  

和

  var myDic4 = [：] 
  

当我声明像myDic4时，我无法添加键值和值：

  myDic4 [001] =ABC
  

错误是无法分配给此表达式的结果

解决方案

您可以通过四种不同的方式声明并初始化Swift中的一个空字典：

1. var myDic1 = [String：AnyObject]（）


2. var myDic2 = Dictionary< String：AnyObject>（）


3. var myDic3：[String：AnyObject] = [：]


4. var myDic4：Dictionary< String：AnyObject& GT; = [：]

这些都会给你相同的结果，这是一个具有 String 作为键， AnyObject 作为值。

[String：AnyObject] 只是 Dictionary< String，AnyObject> 的缩写。他们的意思是同样的事情。

在上述情况1和2中，变量的类型由Swift从分配给它们的值推断出来。在上述情况3和4中，类型被明确地分配给变量，然后用空字典初始化 [：] 。

当您创建这样的字典时：

  var myDic5 = [：] 
  

Swift没有什么可做的，它推断你的字典是类型 NSDictionary 。问题是 NSDictionary 是一个不可变类型（你不能改变它）。可变等价物是一个 NSMutableDictionary ，所以这将工作：

  var myDic6：NSMutableDictionary = [：] 
  

但是，您应该更喜欢使用上面的案例1或3，因为 NSMutableDictionary 不是Swift类型，而是来自Foundation框架。事实上，你甚至可以做 var myDic = [：] 的唯一原因是因为你已经导入了基础框架（使用 import UIKit ， import Cocoa 或 import Foundation ）。没有导入基础，这是一个语法错误。

I really confuse with the way we create dictionary in swift. So could you please tell me what is the different between

var myDic3 = [String : AnyObject]()

and

var myDic2 = Dictionary <Int,AnyObject>()

and

var myDic4 = [ : ]

When i declare like myDic4 I cannot add key and value for it:

myDic4["001"] = "ABC"

And the error is "Cannot assign to the result of this expression"

解决方案

You can declare and initialize an empty Dictionary in Swift in 4 different ways:

1. var myDic1 = [String : AnyObject]()
2. var myDic2 = Dictionary<String: AnyObject>()
3. var myDic3: [String: AnyObject] = [:]
4. var myDic4: Dictionary<String: AnyObject> = [:]

These will all give you the same result which is a Dictionary with Strings as the keys and AnyObjects as the values.

[String: AnyObject] is just shorthand for Dictionary<String, AnyObject>. They mean the same thing.

In cases 1 and 2 above, the types of the variables are inferred by Swift from the values being assigned to them. In cases 3 and 4 above, the types are explicitly assigned to the variables, and then they are initialized with an empty dictionary [:].

When you create a dictionary like this:

var myDic5 = [:]

Swift has nothing to go on, and it infers your dictionary to be of type NSDictionary. The problem is that NSDictionary is an immutable type (you can't change it). The mutable equivalent is an NSMutableDictionary, so this would work:

var myDic6: NSMutableDictionary = [:]

but you should prefer using cases 1 or 3 above since NSMutableDictionary isn't a Swift type but instead comes from the Foundation framework. In fact, the only reason you can even do var myDic = [:] is because you have imported the Foundation framework (with import UIKit, import Cocoa, or import Foundation). Without importing Foundation, this is a syntax error.

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