“强制转换为Any"，但属性的类型为UIColor [英] 'coerced to Any' but property is of type UIColor

问题描述

此

NSAttributedString.Key.foregroundColor: view.tintColor

触发此警告

Expression implicitly coerced from 'UIColor?' to 'Any'

但警告不应该

Expression implicitly coerced from 'UIColor?' to 'UIColor'

由于此属性

NSAttributedString.Key.foregroundColor

是UIColor类型吗?

注意:仅在更新为 Swift 5 ， Xcode 10.2 后才开始发生.

Note: This only started happening after updating to Swift 5, Xcode 10.2.

更多内容:

override func viewDidLoad() {
        super.viewDidLoad()
        UIBarButtonItem.appearance().setTitleTextAttributes(
            [
             NSAttributedString.Key.font: UIFont.systemFont(ofSize: 40),
             NSAttributedString.Key.foregroundColor: view.tintColor
            ], for: .normal)
    }

推荐答案

这与.foregroundColor无关.它与.tintColor和setTitleTextAttributes有关.

This has nothing to do with .foregroundColor. It has everything to do with .tintColor and setTitleTextAttributes.

此参数的类型为[NSAttributedString.Key : Any].绝不考虑每个密钥的文档.它不知道也不在乎这应该是UIColor.如果您通过了"squid"，它将在没有警告的情况下进行编译(虽然不起作用，但会编译):

This parameter is of type [NSAttributedString.Key : Any]. It is not in any way considering the documentation for each key. It doesn't know or care that this should be a UIColor. If you passed "squid", this would compile without warning (it wouldn't work, but it would compile):

UIBarButtonItem.appearance().setTitleTextAttributes(
    [
        .font: UIFont.systemFont(ofSize: 40),
        .foregroundColor: "squid",
    ], for: .normal)

所要查看的是您正在将view.tintColor分配给类型为Any的值.

All it's looking at is that you're assigning view.tintColor to a value of type Any.

问题是view.tintColor不是UIColor，它是UIColor!. .tintColor实际上不可能为nil，但是可以将其设置为nil:

The problem is that view.tintColor is not UIColor, it's UIColor!. It's not actually possible for .tintColor to be nil, but it's possible to set it to nil:

view.tintColor        // r 0.0 g 0.478 b 1.0 a 1.0
view.tintColor = .red
view.tintColor        // r 1.0 g 0.0 b 0.0 a 1.0
view.tintColor = nil
view.tintColor        // r 0.0 g 0.478 b 1.0 a 1.0

在ObjC中有意义，但是在Swift中表达它的唯一方法是使用!类型.当您将!类型分配给其他事物时，它们将成为?类型.这意味着您在接受Any(字典值)的地方使用UIColor?.

That makes sense in ObjC, but the only way to express it in Swift is to use a ! type. When you assign ! types to other things, they become ? types. And that means that you're using UIColor? in a place that accepts Any (the value of the dictionary).

使用可选的Any可能很危险，因为它会产生很多奇怪的极端情况.例如，您不能通过Any来回传递可选内容；它被压缩为基本类型:

Using an optional as Any can be dangerous because it creates a lot of weird corner cases. For example, you can't round-trip an optional through Any; it gets squashed into its base type:

let x: Any = Optional(1)
x as? Int? // Cannot downcast from 'Any' to a more optional type 'Int?'
x as? Int  // 1

与Any一起使用时，会有很多这类小尖锐的边缘.

There are a lot of these kinds of little sharp-edges when working with Any.

当然，您不是平均值与Any一起工作.这不是你的错.但这就是Swift抱怨的原因.

Of course you didn't mean to work with Any. It's not your fault. But this is why Swift is complaining.

有多种解决方案，具体取决于您的喜好.您可以使用!:

There are several solutions, depending on what you like. You can use a !:

    .foregroundColor: view.tintColor!

您可以添加as Any来使警告静音:

You can add as Any to silence the warning:

    .foregroundColor: view.tintColor as Any

我个人会使用as Any.

或者您可以详细说明并更早地卸载该值(我不建议这样做):

Or you can be elaborate and unload the value earlier (I don't recommend this):

let tintColor = view.tintColor ?? .blue

UIBarButtonItem.appearance().setTitleTextAttributes(
    [
        .font: UIFont.systemFont(ofSize: 40),
        .foregroundColor: tintColor,
    ], for: .normal)

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