Swift：计算属性的默认初始化程序 [英] Swift: Default Initializer for Computed Property

问题描述

似乎我无法使用可用于存储属性的Default Initializers方法为计算属性提供默认值。这是一个用例，我需要这个：

It seems like I can't give a computed property a default value using the Default Initializers method that can be used for Stored Properties. Here's a use case where I would need this:

@IBDesignable public class MyRoundedCornersView: UIView {

    @IBInspectable var cornerRadius: CGFloat {
        get {
            return self.layer.cornerRadius
        }
        set {
            self.layer.cornerRadius = newValue
        }
    }

}

我想给cornerRadius是一个默认值。但以下不起作用（只需添加 = 8.0 ）：

I'd like to give the cornerRadius a default value. But the following doesn't work (just added = 8.0):

@IBDesignable public class MyRoundedCornersView: UIView {

    @IBInspectable var cornerRadius: CGFloat = 8.0 {
        get {
            return self.layer.cornerRadius
        }
        set {
            self.layer.cornerRadius = newValue
        }
    }

}

我得到的不太有用'（（） - >（） - > $ T1） - > $ T2'与'Double'错误不同。我查了一下这里以了解如何执行此操作，但Apple似乎不支持计算属性的默认值。至少我找不到任何东西。

I get the not so useful '(() -> () -> $T1) -> $T2' is not identical to 'Double' error. I looked up here to find out how to do this but it seems Apple doesn't support default values for computed properties. At least I couldn't find anything.

那么我怎样才能确保我的财产有默认值？ 此主题表示在init方法中无法实现要么 - 但即使我想保持默认值接近我的属性定义。有没有人有想法？

So how can I still make sure that I have a default value for my property? This thread says it isn't possible within the init method either – but even if, I'd like to keep the default value near my property definition. Does anyone have an idea?

推荐答案

将默认值设置为计算属性因为它没有正确的值：

It doesn't make sense to set a default value to a computed property because it doesn't have a proper value :

[...]计算属性，它们实际上并不存储值。相反，它们提供了一个getter和一个可选的setter来间接检索和设置其他属性和值。

[...] computed properties, which do not actually store a value. Instead, they provide a getter and an optional setter to retrieve and set other properties and values indirectly.

也许你想设置默认值在图层类型中，例如：

Maybe you want to set the default in the layer type, like :

class Layer { // <- The type of layer
    var cornerRadius: CGFloat = 8.0
    // ...
}

另一个解决方案是使用这样的存储属性：

Another solution is to use a stored property like this :

var cornerRadius:CGFloat = 8.0
{
    didSet
    {
        self.layer.cornerRadius = self.cornerRadius
    }
}

编辑：这不保证layer.cornerRadius == self.cornerRadius，特别是如果直接设置了layer.cornerRadius

This does not guarantee that layer.cornerRadius == self.cornerRadius, especially if the layer.cornerRadius is set directly

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