swift – 协议只能用作通用约束

概述我有一个MapViewController用于在地图上显示注释.它包含一个 MapPresentable类型的对象. protocol MapPresentable { associatedtype AnnotationElement: MKAnnotation var annotations: [AnnotationElement] { get }}class MapVie 我有一个MapVIEwController用于在地图上显示注释.它包含一个
MapPresentable类型的对象. @H_419_8@

@H_419_8@

protocol MapPresentable {    associatedtype AnnotationElement: MKAnnotation    var annotations: [AnnotationElement] { get }}class MapVIEwController<M: MapPresentable>: UIVIEwController {    var mapPresentable: M!}

@H_419_8@如果mapPresentable符合RoutePresentable协议,MapVIEwController还可以在地图上显示路线.

@H_419_8@

protocol RoutePresentable: MapPresentable {    var getRouteLocations: [CLLocation] { get }}

@H_419_8@但是在MapVIEwController中进行检查时

@H_419_8@

if let routePresentable = mapPresentable as? RoutePresentable {    showRoute(routePresentable.getRouteLocations)}

@H_419_8@我有这个错误：

@H_419_8@

Protocol 'RoutePresentable' can only be used as a generic constraint because it has Self or associated type requirements

解决方法 更新 @H_419_8@

@H_419_8@对不起,我犯了错误.但是没有办法使用相关类型转换协议.

@H_419_8@希望这会有所帮助.

@H_419_8@据我所知,routePresentable.getRouteLocations与协议MapPresentable无关.

@H_419_8@因此,您可以将RoutePresentable划分为两个协议：

@H_419_8@

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)}

@H_419_8@原版的

@H_419_8@因为routePresentable.annotations的类型未提供,

@H_419_8@您可以删除关联类型AnnotationElement：MKAnnotation.

@H_419_8@或者用户通用结构代替：

@H_419_8@

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)}

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