Swift：“这个类不符合关键值编码......”对于Double值 [英] Swift: "This class is not key value coding-compliant..." for Double values

问题描述

我有一个场景，我在Swift中有一个简单的数据对象，包含多个属性变量。它们是 String？和 Double？值类型的混合。我正在尝试使用 valueForKey 检索每个属性的值。我的代码看起来像这样......

I have a scenario in which I have a simple data object in Swift, containing multiple property variables. They are a mix of String? and Double? value types. I'm trying to retrieve the values for each property using valueForKey. My code looks something like this...

let myDataObj = ...
let stringKeyName = "myStringProperty"
let doubleKeyName = "myDoubleProperty"

guard let stringPropertyValue = myDataObj.valueForKey(stringKeyName) else {
    return
}
guard let doublePropertyValue = myDataObj.valueForKey(doubleKeyName) else {
    return
}

第一次获得 stringPropertyValue 工作正常，我能够按预期检索值。但是，检索 doublePropertyValue 的第二次调用失败，并出现例外情况，此类不符合键值myDoubleProperty的键值编码。 / code>

The first call to get stringPropertyValue works fine, and I am able to retrieve the value as expected. However, the second call to retrieve doublePropertyValue fails with an exception saying, "this class is not key value coding-compliant for the key myDoubleProperty.'"

我知道属性名称是正确的，我也知道为此属性设置了一个值。为什么 valueForKey 适用于 String 对象，但不适用于 Double 对象？

I know that the property name is correct, and I also know that a value is set for this property. Why is it that valueForKey works on String objects, but not Double objects?

推荐答案

正确，您只能对可以在Objective-C中表示的类型进行键值编码。不幸的是，在Objective-C中表示为原始数据类型的那些类型（例如Swift的 Int 和 Double 表示为分别在Objective-C中的NSInteger 和 double 如果是选项，则不能这样表示。在Objective-C中，选项只对类类有意义，而不是基本数据类型。

Correct, you can only do key value coding for types that can be represented in Objective-C. Unfortunately, those types that are represented as primitive data types in Objective-C (e.g. Swift's Int and Double are represented as NSInteger and double in Objective-C, respectively) can not be presented as such if they are optionals. In Objective-C, optionals only make sense with class types, not fundamental data types.

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