在Swift中初始化字典的空数组 [英] Initialising empty arrays of dictionaries in Swift

问题描述

对于一个字符串数组，它很简单：

  var myStringArray：String [] = [] 
 myStringArray + =a
 myStringArray + =b
 
  - > [a，b] 
  

和整数

  var myIntArray：Int [] = [] 
 myIntArray + = 1 
 myIntArray + = 2 
 
  - > ; [1，2] 
  

它还适用于其他类型的对象，如NSImage对象：

  let path =/ Library / Application Support / Apple / iChat图标/标志/
 let image1 = NSImage（byReferencingFile：路径+Brazil.png）
 let image2 = NSImage（byReferencingFile：path +Chile.png）
 
 var myImageArray：NSImage [] = [] 
 myImageArray + = image1 
 myImageArray + = image2 
 
  - > [< NSImage 0x7fe371c199f0 ...>，< NSImage 0x7fe371f39ea0 ...>] 
  

但是，我无法使用语法来初始化一个空的数组字典。

我知道您可以拥有一系列的字典，因为初始化具有初始值：

  let myDict1 = [someKey：someValue] 
 let myDict2 = [anotherKey：anotherValue] 
 
 var myDictArray = [myDict1] 
 myDictArray + = myDict2 
 
  - > [[someKey：someValue]，[anotherKey：anotherValue]] 
  

编辑：在下面的代码中有一个错误（混合myNewDictArray和myDictArray），当更正它不工作，就像我说的那样。

这样做：

  let myDict1 = [someKey：someValue] 
 let myDict2 = [anotherKey：anotherValue] 
 
 var myNewDictArray：AnyObject = [] 
 myDictArray + myDict1 
 myDictArray + = myDict2 
 
  - > [[someKey：someValue]，[anotherKey：anotherValue]] 
  

然而（你希望语法是）会失败：

  var myNewDictArray：Dictionary [] = [] 
  

code>不能将表达式的类型'Dictionary []转换为'Hashable'类型

所以问题是什么是正确的初始化一个空数组的字典项目的方式，为什么这个语法不是 var myNewDictArray：Dictionary [] = [] work？

解决方案

你需要给字典类型：

  var myNewDictArray ：[Dictionary< String，Int>] = [] 
  

或

  var myNewDictArray = [Dictionary< String，Int>]（）
  

编辑：您也可以使用较短的语法：

  var myNewDictArray：[[String：Int]] = [] 
  

或

  var myNewDictArray = [[String：Int]]（）
  

I'm trying to wrap my head around initialising empty arrays in Swift.

For an array of strings it's pretty straight forward :

var myStringArray: String[] = []
myStringArray += "a"
myStringArray += "b"

-> ["a", "b"]

and for integers

var myIntArray: Int[] = []
myIntArray += 1
myIntArray += 2

-> [1, 2]

it also works for other types of object such as NSImage objects :

let path = "/Library/Application Support/Apple/iChat Icons/Flags/"
let image1 = NSImage(byReferencingFile: path + "Brazil.png")
let image2 = NSImage(byReferencingFile: path + "Chile.png")

var myImageArray: NSImage[] = []
myImageArray += image1
myImageArray += image2

-> [<NSImage 0x7fe371c199f0 ...>, <NSImage 0x7fe371f39ea0 ...>]

However I can't work out the syntax to initialise an empty array of Dictionaries.

I know you can have an array of Dictionaries because initialising with an initial value works :

let myDict1 = ["someKey":"someValue"]
let myDict2 = ["anotherKey":"anotherValue"]

var myDictArray = [myDict1]
myDictArray += myDict2

-> [["someKey": "someValue"], ["anotherKey": "anotherValue"]]

EDIT : There was an error in the following code (mixing myNewDictArray and myDictArray) and when corrected it doesn't work as I said it did.

as does this :

let myDict1 = ["someKey":"someValue"]
let myDict2 = ["anotherKey":"anotherValue"]

var myNewDictArray: AnyObject = []
myDictArray += myDict1
myDictArray += myDict2

-> [["someKey": "someValue"], ["anotherKey": "anotherValue"]]

This however (which you'd expect the syntax to be) fails :

var myNewDictArray: Dictionary[] = []

with the error Cannot convert the expression's type 'Dictionary[]' to type 'Hashable'

So the question is what is the correct way to initialise a empty array of Dictionary Items and why doesn't this syntax var myNewDictArray: Dictionary[] = [] work?

解决方案

You need to give types to the dictionaries:

var myNewDictArray: [Dictionary<String, Int>] = []

or

var myNewDictArray = [Dictionary<String, Int>]()

Edit: You can also use the shorter syntax:

var myNewDictArray: [[String:Int]] = []

or

var myNewDictArray = [[String:Int]]()

这篇关于在Swift中初始化字典的空数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！