Question

我正在尝试确定类层次结构中对象的类。我很想解释为什么下面例子中的测试失败。

    class BasicLocation {}
        class AddressLocation : BasicLocation {}
        class ContactLocation : BasicLocation {}

        func mapView(_ mapView : MKMapView, viewFor: MKAnnotation)
        ->MKAnnotationView?{
        if let test = viewFor as? BasicLocation {
            let basicType = BasicLocation()
            let a = type(of:test)
            let b = type(of:basicType)
            let c = type(of:test)
            NSLog("a=\(a), type of a=\(type(of:a))")
            NSLog("b=\(b), type of b=\(type(of:b))")
            NSLog("c=\(c), type of b=\(type(of:c))")
            if a == b {
                NSLog("passed a and b")
            } else {
               NSLog("a and b do not match match")
            }
            if a == c {
                NSLog("passed a and c")
            }

output

>a=BasicLocation, type of a=BasicLocation.Type  
>b=BasicLocation, type of b=BasicLocation.Type  
>c=BasicLocation, type of b=BasicLocation.Type  
>a and b do not match match  
>a and c natch

Answer 1

说完后

if let test = viewFor as? BasicLocation

......如果该测试通过，请停止。您现在知道test是BasicLocation实例，或者我们不会通过测试。

你正在做的其他事情都很愚蠢。元类型之间的平等比较是不确定的。

确定Swift类的类型

1 个答案: