Delphi SysUtils。支持意外返回true

发生这种情况的原因是,如果在泛型接口上放置guid,则该接口的每个专门化都将具有相同的guid,而不管其泛型类型参数如何。

我通常通过在界面中提供相关信息来解决这个问题(如 Spring.Collections.IEnumerable 具有 ElementType 属性来获取 IEnumerable<T> ).

因此,实现如下所示:

program GenericEventPublisher;

{$APPTYPE CONSOLE}

uses
  Spring,
  Spring.Collections,
  System.SysUtils;

type
  IEventHandler = interface
    ['{2E4BD8F4-4EB8-4B33-84F4-B70F42EF9208}']
    procedure Handle(const event: TObject);
  end;

  IEventHandler<T: class> = interface
    ['{82B7521E-D719-4051-BE2C-2EC449A92B22}']
    procedure Handle(const event: T);
    function GetHandledClass: TClass;
  end;

  IEventPublisher = interface
    ['{2A460EF0-AE27-480F-ACEA-1B897F2DE056}']
    procedure Subscribe(const subscriber: IEventHandler);
    procedure Publish(const event: TObject; ownsObject: Boolean = True);
  end;

  TEventHandlerBase<T: class> = class(TInterfacedObject, IEventHandler, IEventHandler<T>)
  private
    function GetHandledClass: TClass;
    procedure Handle(const event: TObject); overload;
  public
    procedure Handle(const event: T); overload; virtual; abstract;
  end;

  TEvent1 = class
  end;

  TEvent2 = class
  end;

  TMyEventHandler1 = class(TEventHandlerBase<TEvent1>)
  public
    procedure Handle(const event: TEvent1); override;
  end;

  TMyEventHandler2 = class(TEventHandlerBase<TEvent2>)
  public
    procedure Handle(const event: TEvent2); override;
  end;

  TEventPublisher = class(TInterfacedObject, IEventPublisher)
  private
    fSubscribers: IList<IEventHandler>;
  public
    constructor Create;
    procedure Subscribe(const subscriber: IEventHandler);
    procedure Publish(const event: TObject; ownsObject: Boolean = True);
  end;

{ TEventPublisher }

constructor TEventPublisher.Create;
begin
  fSubscribers := TCollections.CreateList<IEventHandler>;
end;

procedure TEventPublisher.Publish(const event: TObject; ownsObject: Boolean);
var
  subscriber: IEventHandler;
  eventSubscriber: IEventHandler<TObject>;
begin
  for subscriber in fSubscribers do
    if Supports(subscriber, IEventHandler<TObject>, eventSubscriber)
      and (eventSubscriber.GetHandledClass = event.ClassType) then
        eventSubscriber.Handle(event);

  if ownsObject then
    event.Free;
end;

procedure TEventPublisher.Subscribe(const subscriber: IEventHandler);
begin
  fSubscribers.Add(subscriber)
end;

{ TEventHandlerBase<T> }

function TEventHandlerBase<T>.GetHandledClass: TClass;
begin
  Result := T;
end;

procedure TEventHandlerBase<T>.Handle(const event: TObject);
begin
  Assert(event is T);
  Handle(T(event));
end;

{ TMyEventHandler1 }

procedure TMyEventHandler1.Handle(const event: TEvent1);
begin
  Writeln(event.ClassName, ' handled by ', ClassName);
end;

{ TMyEventHandler2 }

procedure TMyEventHandler2.Handle(const event: TEvent2);
begin
  Writeln(event.ClassName, ' handled by ', ClassName);
end;

var
  eventPublisher: IEventPublisher;
begin
  eventPublisher := TEventPublisher.Create;
  eventPublisher.Subscribe(TMyEventHandler1.Create);
  eventPublisher.Subscribe(TMyEventHandler2.Create);
  eventPublisher.Publish(TEvent1.Create);
  eventPublisher.Publish(TEvent2.Create);
end.

由于接口上有类约束,我们可以确保接口是二进制兼容的,无论T的类型如何(因为它们只能是对象)。同时,为通用事件处理程序使用基类型可以减少编写的额外代码。它只是重定向非泛型 Handle 方法转换为必须在具体实现中实现的通用方法。

此外,由于基类实现了这两个接口,我们不需要将处理程序存储在 TValue 但是可以使用非通用接口类型,并且无需RTTI即可轻松访问它们。

现在 Publish 方法正在使用小技巧调用 Support 具有 IEventHandler<TObject> -自 eventSubscriber 是那种我们可以通过 event its的参数 手柄 方法恰好是正确的,这是因为我之前解释过的二进制兼容性,因为我们只是处理不同的类,因为如果没有类约束,T-story的类型将完全不同。