如何在Swift字典中添加nil值? [英] How to add nil value to Swift Dictionary?

问题描述

我已经在我的应用中向服务器提出了请求.然后像这样发布数据.服务器端正在等待所有参数，即使它们为零.但是我无法将nil值添加到字典中.

I have made a request to my server in my app. And posted data something like this.Server side is waiting for all parameters even they are nil. But i couldn't add nil values to dictionary.

 var postDict = Dictionary<String,AnyObject>
 postDict[pass]=123
 postDict[name]="ali"
 postDict[surname]=nil // dictionary still has only pass and name variables.

有没有一种方法可以将nil值添加到字典中?

Is there a way to add nil value to dictionary ?

推荐答案

如何在Swift字典中添加nil值?

基本上与您将其他任何值添加到字典的方式相同.您首先需要一个字典，该字典的值类型可以保存您的值.类型AnyObject不能具有值nil.因此，类型为[String : AnyObject]的字典不​​能具有值nil.

Basically the same way you add any other value to a dictionary. You first need a dictionary which has a value type that can hold your value. The type AnyObject cannot have a value nil. So a dictionary of type [String : AnyObject] cannot have a value nil.

如果您的字典的值类型是可选类型，例如[String : AnyObject?]，则它可以容纳nil值.例如，

If you had a dictionary with a value type that was an optional type, like [String : AnyObject?], then it can hold nil values. For example,

let x : [String : AnyObject?] = ["foo" : nil]

如果您要使用下标语法来分配元素，则有些棘手.请注意，类型[K:V]的下标具有类型V?.可选的是，当您找到它时，它指示是否有该键的条目，如果有，则指示该值；并将其放入后，您可以设置一个值或删除该条目(通过分配nil).

If you want to use the subscript syntax to assign an element, it is a little tricky. Note that a subscript of type [K:V] has type V?. The optional is for, when you get it out, indicating whether there is an entry for that key or not, and if so, the value; and when you put it in, it allows you to either set a value or remove the entry (by assigning nil).

这意味着对于我们的类型为[String : AnyObject?]的字典，下标的类型为AnyObject??.同样，当您在下标中输入值时，外部"可选选项允许您设置值或删除条目.如果我们只是写

That means for our dictionary of type [String : AnyObject?], the subscript has type AnyObject??. Again, when you put a value into the subscript, the "outer" optional allows you to set a value or remove the entry. If we simply wrote

x["foo"] = nil

编译器推断出它是类型为AnyObject??的nil(外部可选)，这意味着删除键"foo"的条目.

the compiler infers that to be nil of type AnyObject??, the outer optional, which would mean remove the entry for key "foo".

为了将键"foo"的值设置为AnyObject?值nil，我们需要传入一个非nil外部可选内容，其中包含一个内部可选内容(值nil的AnyObject?类型).为此，我们可以

In order to set the value for key "foo" to the AnyObject? value nil, we need to pass in a non-nil outer optional, containing an inner optional (of type AnyObject?) of value nil. In order to do this, we can do

let v : AnyObject? = nil
x["foo"] = v

或

x["foo"] = nil as AnyObject?

表明我们的nil为AnyObject?而不是AnyObject??的任何内容.

Anything that indicates that we have a nil of AnyObject?, and not AnyObject??.

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