如何在Swift中测试变量的类? [英] How to test for the class of a variable in Swift?

问题描述

我想检查数组的元素是否是Swift中UILabel的子类:

I want to check if the elements of an Array are a subclass of UILabel in Swift:

import UIKit

var u1 = UILabel()
u1.text="hello"
var u2 = UIView(frame: CGRectMake(0, 0, 200, 20))
var u3 = UITableView(frame: CGRectMake(0, 20, 200, 80))

var myArray = [u1, u2, u3]

var onlyUILabels = myArray.filter({"what to put here?"})

不与目标c搭桥.

推荐答案

Swift具有is运算符来测试值的类型:

Swift has the is operator to test the type of a value:

var onlyUILabels = myArray.filter { $0 is UILabel }

作为旁注，这仍将生成Array<UIView>，而不是Array<UILabel>.从Swift 2 beta系列开始，您可以为此使用flatMap:

As a side note, this will still produce an Array<UIView>, not Array<UILabel>. As of the Swift 2 beta series, you can use flatMap for this:

var onlyUILabels = myArray.flatMap { $0 as? UILabel }

以前(快速1)，您可以投射，虽然可以，但是感觉有点难看.

Previously (Swift 1), you could cast, which works but feels a bit ugly.

var onlyUILabels = myArray.filter { $0 is UILabel } as! Array<UILabel>

否则，您需要某种方式来构建仅包含标签的列表.不过，我看不到任何标准.也许像这样:

Or else you need some way to build a list of just the labels. I don't see anything standard, though. Maybe something like:

extension Array {
    func mapOptional<U>(f: (T -> U?)) -> Array<U> {
        var result = Array<U>()
        for original in self {
            let transformed: U? = f(original)
            if let transformed = transformed {
                result.append(transformed)
            }
        }
        return result
    }
}
var onlyUILabels = myArray.mapOptional { $0 as? UILabel }

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