ios 如何在 Swift 中测试变量的类？
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How to test for the class of a variable in Swift?
提问by ielyamani
I want to check if the elements of an Array are a subclass of UILabel in Swift:
我想检查 Array 的元素是否是 Swift 中 UILabel 的子类：
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?"})
Without bridging to objective-c.
没有桥接到objective-c。
回答by Jesse Rusak
Swift has the isoperator to test the type of a value:
Swift 有一个is操作符来测试一个值的类型：
var onlyUILabels = myArray.filter { var onlyUILabels = myArray.flatMap { var onlyUILabels = myArray.filter { 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 { var (a,b,c,d) = ("String", 42, 10.0, "secondString")
let myArray: Array<Any> = [a,b,c,d]
var onlyStrings = myArray.filter({ return let objectClass: AnyClass = object_getClass(object) as AnyClass
let objectClassName = NSStringFromClass(objectClass)
println("Class = \(objectClassName)")
is String })
onlyStrings // ["String", "secondString"]
as? UILabel }
is UILabel } as! Array<UILabel>
as? UILabel }
is UILabel }
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:
作为旁注，这仍然会产生一个Array<UIView>，而不是Array<UILabel>。从 Swift 2 beta 系列开始，您可以为此使用 flatMap：
UILabel // UILabel
Swift._NSSwiftArrayImpl //Swift Array
MyProject.Customer_Customer_ //for a CoreData class named Customer
Previously (Swift 1), you could cast, which works but feels a bit ugly.
以前（Swift 1），您可以投射，这有效但感觉有点难看。
return object.dynamicType == otherObject.dynamicType
Or else you need some way to build a list of just the labels. I don't see anything standard, though. Maybe something like:
否则，您需要某种方法来构建仅包含标签的列表。不过，我看不出任何标准。也许是这样的：
##代码##回答by wottpal
In Swift you should do the iskeyword if you are wondering about the according class. In the filter-closure you can use $0to specify the first parameter.
在 Swift 中，is如果您想知道相应的类，您应该使用关键字。在filter-closure 中，您可以$0用来指定第一个参数。
Sample
样本
##代码##回答by eharo2
Without getting to the object.class( ) nirvana, in Swift, we can still use the Objective-C Runtime to get some useful information about the object′s class as follows (and not exactly bridging to Objective-C):
没有进入 object.class() 的必杀技，在 Swift 中，我们仍然可以使用 Objective-C 运行时来获取有关对象类的一些有用信息，如下所示（并不完全桥接到 Objective-C）：
##代码##Note that we get the "MyProject." or (sometimes) the "Swift." prefix, depending if you refer to your own classes or Swift classes:
请注意，我们得到了“MyProject”。或（有时）“斯威夫特”。前缀，取决于您是指自己的类还是 Swift 类：
##代码##回答by TheCodingArt
You may compare classes using the following in swift:
您可以在 swift 中使用以下内容比较类：
##代码##dynamicType will return an instance of Class which you may compare
dynamicType 将返回一个您可以比较的 Class 实例
