如何将NSDictionary转换为Swift字典< String，NSObject&gt ;? [英] How do I convert an NSDictionary to a Swift Dictionary<String, NSObject>?

问题描述

我在Swift中重写一个Objective-C类，以获得对语言的感觉。在Objective-C我的类包括以下方法：

I am rewriting an Objective-C class in Swift to get a feel for the language. In Objective-C my class included the following method:

- (id) initWithCoder:(NSCoder *)aDecoder
{
    return [self initWithActionName:[aDecoder decodeObjectOfClass:[NSString class] forKey:@"actionName"]
                            payload:[aDecoder decodeObjectOfClass:[NSDictionary class] forKey:@"payload"]
                          timestamp:[aDecoder decodeObjectOfClass:[NSDate class] forKey:@"timestamp"]];
}

在编译器尝试和错误之后，我设法重写它：

After some trial and error with the compiler, I managed to rewrite it like this:

convenience init(aDecoder: NSCoder) {
    let actionName = aDecoder.decodeObjectOfClass(NSString.self, forKey: "actionName") as NSString
    let payload = aDecoder.decodeObjectOfClass(NSDictionary.self, forKey: "payload") as NSDictionary
    let timestamp = aDecoder.decodeObjectOfClass(NSDate.self, forKey: "timestamp") as NSDate
    self.init(actionName: actionName, payload: payload, timestamp: timestamp)
}

b $ b

但是，这仍然给我最后一行的错误：找不到重载 init ，接受提供的参数。方法签名 init 是

However, this still gives me an error on the last line: "Could not find an overload for init that accepts the supplied arguments." The method signature of init is

init(actionName: String, payload: Dictionary<String, NSObject>, timestamp: NSDate)

所以我假设问题是我试图通过 NSDictionary 而不是 Dictionary< String，NSObject> 。如何在这两个不完全等价类型之间进行转换？我应该对所有必须与其他Objective-C组件交互的代码使用 NSDictionary 吗？

so I assume the problem is that I am trying to pass an NSDictionary instead of a Dictionary<String, NSObject>. How can I convert between these two not-quite-equivalent types? Should I just be using NSDictionary for all of the code that has to interact with other Objective-C components?

推荐答案

将字典解码为 Dictionary< String，NSObject> ，而不是 NSDictionary 。

Decode your dictionary as Dictionary<String, NSObject> instead of NSDictionary.

let payload = aDecoder.decodeObjectOfClass(NSDictionary.self, forKey: "payload") as! Dictionary<String, NSObject>

由于您使用Cocoa Touch进行序列化和反序列化，所以序列化为 NSDictionary ，但是你可以将它转换为Swift 字典<，> ，根据WWDC 2014 中介Swift

Since you are using Cocoa Touch to serialize and deserialize, they are serialized as NSDictionary, but you can cast it to a Swift Dictionary<,>, as per WWDC 2014 Intermediary Swift and Advanced Swift videos.

您还可以解码为 NSDictionary ，然后显式强制转换对象如下：

You can also decode as NSDictionary and then explicitly cast the object like so:

self.init(actionName: actionName, payload: payload as! Dictionary<String, NSObject>, timestamp: timestamp)

基本上，你在这里玩协方差/逆变。

Basically, you are playing here with covariance/contravariance.

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