将非可选的 Any 与 nil 进行比较总是错误的？

Question

I'm iterating through a dictionary of [String: Any]<\/code> , looking for nil<\/code> s, so I can replace them with NSNull<\/code> for a JSON write. My precompiler warning is telling me that comparing an Any<\/code> to a nil<\/code> will always be false, but I know it contains at least two nils which are never found. Is there a way to check is an Any<\/code> is nil?

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Answer 1

An Optional can be nil . Anything else can never be nil . An Any is not an Optional. Thus there is no point comparing an Any to nil . The test will never succeed.

If you know that these things might be Optionals, you should have typed this as Any? . That is an Optional and can be compared to nil . Here's a simple example:

    let s : String? = nil
    let any : Any? = s
    if any == nil {
        print("nil") // nil
    }

As you can see, the test succeeds.

(Still, if at all possible, it would be even better to type things more precisely.)

Answer 2

我已经使用波纹管表达式解决了这个问题：

let filteredResult = dictionary.filter { !(($0.value as AnyObject) is NSNull) }

Answer 3

if(object_getClass(yourVariable)?.description() == "NSNull")可以是检查的方法之一。

Answer 4

Objective-c property in swift. If you're using some objective c property in swift and it says something like "Comparing non-optional value of type 'XYZ' to 'nil' always returns true" you have to make that objective c property to "_Nullable" so that property may not be optional anymore. Like @property (strong,nonatomic) NSString *_Nullable someString;