swift – 协议只能用作通用约束

对不起,我犯了错误.但是没有办法使用相关类型转换协议.

希望这会有所帮助.

据我所知,routePresentable.getRouteLOCATIOns与协议MapPresentable无关.

因此,您可以将RoutePresentable划分为两个协议：

protocol MapPresentable {
    associatedtype AnnotationElement: MKAnnotation
    var Annotations: [AnnotationElement] { get }
}

class MapViewController<M: MapPresentable>: UIViewController {
    var mapPresentable: M!

}

protocol RoutePresentable: MapPresentable,CanGetRouteLOCATIOns {}

protocol CanGetRouteLOCATIOns {
    var getRouteLOCATIOns: [CLLOCATIOn] { get }
}


if let routePresentable = mapPresentable as? CanGetRouteLOCATIOns {
    showRoute(routePresentable.getRouteLOCATIOns)
}

原版的

因为routePresentable.Annotations的类型未提供,

您可以删除关联类型AnnotationElement：MKAnnotation.

或者用户通用结构代替：

struct MapPresentable<AnnotationElement: MKAnnotation> {
    var Annotations: [AnnotationElement] = []
}

struct RoutePresentable<AnnotationElement: MKAnnotation> {
    var mapPresentable: MapPresentable<AnnotationElement>
    var getRouteLOCATIOns: [CLLOCATIOn] = []
}

class MapViewController<AnnotationElement: MKAnnotation>: UIViewController {

    var mapPresentable: MapPresentable<AnnotationElement>!

}

if let routePresentable = mapPresentable as? RoutePresentable<MKAnnotation> {
    showRoute(routePresentable.getRouteLOCATIOns)
}