如何将NSMutableArray转换为特定类型的Swift数组？ [英] How can I cast an NSMutableArray to a Swift array of a specific type?

问题描述

我正在将我的iOS项目迁移到Swift。我是按班做的。当我从Swift调用Objective C方法时，很多Objective C类型被转换为它们的Swift对应物。

I am migrating my iOS project to Swift. I am doing this class by class. When I call Objective C methods from Swift, a lot of Objective C types are converted to their Swift counterparts.

在我的例子中，Objective C NSMutableArray 转换为Swift的数组< AnyObject> 。现在我的问题来了。在我的Swift类中，我从Objective C对象中获取了这样一个数组。现在我在Swift世界中，我想将此数组转换为特定类型而不是 AnyObject ，因为我确定该数组中存在哪种对象。

In my case an Objective C NSMutableArray gets converted to Swift's Array<AnyObject>. Now here comes my problem. Within my Swift class, I get such an array back from an Objective C object. Now that I am in the Swift world, I would like to cast this array to a specific type instead of AnyObject, because I know for sure what kind of objects exist in this array.

编译器不允许我这样做！让我通过说我想要转换为包含字符串的数组来简化我的问题。这就是我试过的：

The compiler won't let me do that! Let me simplify my problem by saying I want to cast to an array containing strings. This is what I tried:

var strings = myObjcObject.getStrings() as [String]

我从编译器收到以下错误：

I get the following error from the compiler:

'String'与'AnyObject'不相同

'String' is not identical to 'AnyObject'

我必须同意编译器，因为String确实不相同到AnyObject。但我不明白为什么这是一个问题。如果我愿意，我可以将AnyObject转发给String，对吗？

I would have to agree with the compiler, since String is indeed not identical to AnyObject. But I don't see why that is a problem. I can downcast AnyObject to String if I want, right?

我也尝试过：

var strings = myObjcObject.getStrings() as? [String]

这似乎是朝着正确方向迈出的一步，但getStrings（）返回一个 NSMutableArray 所以我收到以下错误：

This seems to be a step in the right direction, but getStrings() returns an NSMutableArray so I get the following error:

'NSArray'不是子类型'NSMutableArray'

'NSArray' is not a subtype of 'NSMutableArray'

有什么方法可以做我想在这里做的事情吗？

Is there any way to do what I am trying to do here?

推荐答案

你可以使用双向下转换，首先到 NSArray ，再到 [String] ：

You can make this work with a double downcast, first to NSArray, then to [String]:

var strings = myObjcObject.getStrings() as NSArray as [String]

在游乐场测试：

import Foundation

var objCMutableArray = NSMutableArray(array: ["a", "b", "c"])
var swiftArray = objCMutableArray as NSArray as [String]

更新：

在Swift的后续版本（至少1.2）中，编译器会抱怨为[String] 。相反，你应该使用如果让与条件下击一样？：

In later versions of Swift (at least 1.2), the compiler will complain about as [String]. Instead you should use an if let with a conditional downcast as?:

import Foundation

var objCMutableArray = NSMutableArray(array: ["a", "b", "c"])
if let swiftArray = objCMutableArray as NSArray as? [String] {
    // Use swiftArray here
}

如果你是 绝对 确保您的 NSMutableArray 可以投放到 [String] ，然后你可以使用作为！（但在大多数情况下你可能不应该使用它）：

If you are absolutely sure that your NSMutableArray can be cast to [String], then you can use as! instead (but you probably shouldn't use this in most cases):

import Foundation

var objCMutableArray = NSMutableArray(array: ["a", "b", "c"])
var swiftArray = objCMutableArray as NSArray as! [String]

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