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如何测试泛型接口的类型？

delphigenerics
4

我不确定标题是否有意义，但我希望您能通过一些代码理解我的问题。

给定以下发布/订阅框架的代码。

type
  IMessage = interface
    ['{B1794F44-F6EE-4E7B-849A-995F05897E1C}']
  end;

  ISubscriber = interface
    ['{D655967E-90C6-4613-92C5-1E5B53619EE0}']
  end;

  ISubscriberOf<T: IMessage> = interface(ISubscriber)
    procedure Consume(const message: T);
  end;

  TMessageService = class
  private
    FSubscribers: TList<ISubscriber>;
  public
    constructor Create;
    destructor Destroy; override;
    procedure SendMessage(const message: IMessage);
    procedure Subscribe(const Subscriber: ISubscriber);
    procedure Unsubscribe(const Subscriber: ISubscriber);
  end;

这将会像这样使用：

TMyMessage = class(TInterfacedObject, IMessage);

TMySubscriber = class(TInterfacedObject, ISubscriberOf<TMyMessage>)
  procedure Consume(const Message: TMyMessage);
end;

TMyOtherMessage = class(TInterfacedObject, IMessage);

TMyOtherSubscriber = class(TInterfacedObject, ISubscriberOf<TMyOtherMessage>)
  procedure Consume(const Message: TOtherMessage);
end;

如何循环订阅者列表并将消息发送给正确的订阅者？

订阅者列表将包含所有类型消息的订阅者。SendMessage必须查找提供的参数类型的订阅者，并将其发送给实现适当接口以消耗该类型消息的人。

  procedure TMessageService.SendMessage(const message: IMessage);
  var
    Subscriber: ISubscriber;
  begin
    for Subscriber in FSubscribers do
    begin
      // How to send the message only to the subscribers of the correspondent type of message
    end;
  end;

谢谢！

顺便说一下，这段代码基于这篇博客文章。

1
很难知道你的问题是什么，以及你所说的“适当的订阅者”是什么意思。很难找到动力去阅读你链接的博客文章。如果你能尽可能简洁地总结一下，那么你可能会更有帮助。 - David Heffernan
谢谢 @David，我已经添加了更多的信息来尝试解释我想要什么。 - Erick Sasse
让TMessageService.SendMessage将消息发送给每个订阅者，让订阅者的Consume方法决定是否处理它或忽略它，这样不是更容易吗？ - Kenneth Cochran
@codeelegance可能更简单，但在我看来是一种糟糕的实现。如果同一个对象订阅了多个消息，那么就需要一个大的if或case语句。 - Erick Sasse
1个回答
4

编辑：找到了一种使这个过程更简单的方法（如果您喜欢这个答案，请投票支持；我花了很长时间才搞定）。
请注意，它使用了新的Rtti单元，因此仅适用于Delphi 2010及以上版本（我在Delphi XE中开发了这个，但尚未在Delphi 2010中验证）。

对于Supports，您需要存储一些IID GUID与您的接口以及查询它们的方法。
由于您希望将其与泛型一起使用，因此要能够从接口类型而不是接口引用中查询IID GUID（正如Hallvard Vassbotn在2006年通过hack所示）。
Delphi 2010中引入的新RTTI正好可以做到这一点：

unit RttiUnit;

interface

type
  TRtti = record
    //1 similar to http://hallvards.blogspot.com/2006/09/hack11-get-guid-of-interface-reference.html but for the interface type, not for a reference
    class function GetInterfaceIID<T: IInterface>(var IID: TGUID): Boolean; static;
  end;

implementation

uses
  TypInfo,
  Rtti;

class function TRtti.GetInterfaceIID<T>(var IID: TGUID): Boolean;
var
  TypeInfoOfT: PTypeInfo;
  RttiContext: TRttiContext;
  RttiInterfaceType: TRttiInterfaceType;
  RttiType: TRttiType;
begin
  TypeInfoOfT := TypeInfo(T);
  RttiContext := TRttiContext.Create();

  RttiType := RttiContext.GetType(TypeInfoOfT);
  if RttiType is TRttiInterfaceType then
  begin
    RttiInterfaceType := RttiType as TRttiInterfaceType;
    IID := RttiInterfaceType.GUID;
    Result := True;
  end
  else
    Result := False;
end;

end.

现在是更改后的代码，我稍微重新排列了一下，并将其分散到更多单元中以保持概览。

ClassicMessageSubscriberUnit：具有非泛型接口IMessage和ISubscriber（它们都派生自IImplementedWithClass，这使得记录事务更加容易。

unit ClassicMessageSubscriberUnit;

interface

type
  IImplementedWithClass = interface(IInterface)
    function ToString: string;
  end;

  IMessage = interface(IImplementedWithClass)
    ['{B1794F44-F6EE-4E7B-849A-995F05897E1C}']
  end;

  ISubscriber = interface(IImplementedWithClass)
    ['{D655967E-90C6-4613-92C5-1E5B53619EE0}']
  end;

implementation

end.

GenericSubscriberOfUnit：包含通用的ISubscriberOf接口，该接口派生自通用的ISupporterOf接口和一个名为TSupporterOf的通用基础实现：

unit GenericSubscriberOfUnit;

interface

uses
  ClassicMessageSubscriberUnit;

type
  ISupporterOf<T: IMessage> = interface(ISubscriber)
    ['{0905B3EB-B17E-4AD2-98E2-16F05D19484C}']
    function Supports(const Message: T): Boolean;
  end;

  ISubscriberOf<T: IMessage> = interface(ISupporterOf<T>)
    ['{6FD82B1D-61C6-4572-BA7D-D70DA9A73285}']
    procedure Consume(const Message: T);
  end;

type
  TSupporterOf<T: IMessage> = class(TInterfacedObject, ISubscriber, ISupporterOf<T>)
    function Supports(const Message: T): Boolean;
  end;

implementation

uses
  SysUtils,
  RttiUnit;

function TSupporterOf<T>.Supports(const Message: T): Boolean;
var
  IID: TGUID;
begin
  if TRtti.GetInterfaceIID<T>(IID) then
    Result := SysUtils.Supports(Message, IID)
  else
    Result := False;
end;

end.

MessageServiceUnit：现在仅包含TMessageService、一些类型别名和实际代码，用于管理列表以便我可以进行实际测试。

unit MessageServiceUnit;

interface

uses
  Generics.Collections,
  ClassicMessageSubscriberUnit,
  GenericSubscriberOfUnit;

type
  ISubscriberOfIMessage = ISubscriberOf<IMessage>;
  TListISubscriber = TList<ISubscriber>;

  TMessageService = class
  private
    FSubscribers: TListISubscriber;
  strict protected
    procedure Consume(const SubscriberOf: ISubscriberOfIMessage; const Message: IMessage); virtual;
  public
    constructor Create;
    destructor Destroy; override;
    procedure SendMessage(const Message: IMessage);
    procedure Subscribe(const Subscriber: ISubscriber);
    procedure Unsubscribe(const Subscriber: ISubscriber);
  end;

implementation

uses
  SysUtils;

constructor TMessageService.Create;
begin
  inherited Create();
  FSubscribers := TListISubscriber.Create();
end;

destructor TMessageService.Destroy;
begin
  FreeAndNil(FSubscribers);
  inherited Destroy();
end;

procedure TMessageService.SendMessage(const Message: IMessage);
var
  LocalMessage: IMessage;
  lSubscriber: ISubscriber;
  lSubscriberOf: ISubscriberOf<IMessage>;
begin
  for lSubscriber in FSubscribers do
  begin
    LocalMessage := Message; // to prevent premature freeing of Message
    if Supports(lSubscriber, ISubscriberOf<IMessage>, lSubscriberOf) then
      if lSubscriberOf.Supports(LocalMessage) then
        Consume(lSubscriberOf, LocalMessage);
  end;
end;

procedure TMessageService.Subscribe(const Subscriber: ISubscriber);
begin
  FSubscribers.Add(Subscriber);
end;

procedure TMessageService.Unsubscribe(const Subscriber: ISubscriber);
begin
  FSubscribers.Remove(Subscriber);
end;

procedure TMessageService.Consume(const SubscriberOf: ISubscriberOfIMessage; const Message: IMessage);
begin
  SubscriberOf.Consume(Message);
end;

end.

最后，我使用了一个单元来测试所有内容（它使用了位于http://bo.codeplex.com的bo-library）：

unit GenericPublishSubscribeMainFormUnit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, LoggerInterfaceUnit, MessageServiceUnit,
  MessageSubscribersUnit, ClassicMessageSubscriberUnit;

type
  TGenericPublishSubscribeMainForm = class(TForm)
    TestPublisherButton: TButton;
    LogMemo: TMemo;
    procedure TestPublisherButtonClick(Sender: TObject);
  strict private
    FLogger: ILogger;
  strict protected
    function GetLogger: ILogger;
    property Logger: ILogger read GetLogger;
  public
    destructor Destroy; override;
  end;

type
  TLoggingMessageService = class(TMessageService)
  strict private
    FLogger: ILogger;
  strict protected
    procedure Consume(const SubscriberOf: ISubscriberOfIMessage; const Message: IMessage); override;
  public
    constructor Create(const Logger: ILogger);
    property Logger: ILogger read FLogger;
  end;

var
  GenericPublishSubscribeMainForm: TGenericPublishSubscribeMainForm;

implementation

uses
  LoggerUnit,
  OutputDebugViewLoggerUnit,
  LoggersUnit,
  MessagesUnit;

{$R *.dfm}

destructor TGenericPublishSubscribeMainForm.Destroy;
begin
  inherited Destroy;
  FLogger := nil;
end;

function TGenericPublishSubscribeMainForm.GetLogger: ILogger;
begin
  if not Assigned(FLogger) then
    FLogger :=  TTeeLogger.Create([
      TOutputDebugViewLogger.Create(),
      TStringsLogger.Create(LogMemo.Lines)
    ]);
  Result := FLogger;
end;

procedure TGenericPublishSubscribeMainForm.TestPublisherButtonClick(Sender: TObject);
var
  LoggingMessageService: TLoggingMessageService;
begin
  LoggingMessageService := TLoggingMessageService.Create(Logger);
  try
    LoggingMessageService.Subscribe(TMySubscriber.Create() as ISubscriber);
    LoggingMessageService.Subscribe(TMyOtherSubscriber.Create() as ISubscriber);
    LoggingMessageService.SendMessage(TMyMessage.Create());
    LoggingMessageService.SendMessage(TMyOtherMessage.Create());
  finally
    LoggingMessageService.Free;
  end;
end;

constructor TLoggingMessageService.Create(const Logger: ILogger);
begin
  inherited Create();
  FLogger := Logger;
end;

procedure TLoggingMessageService.Consume(const SubscriberOf: ISubscriberOfIMessage; const Message: IMessage);
var
  MessageImplementedWithClass: IImplementedWithClass;
  MessageString: string;
  SubscribeImplementedWithClass: IImplementedWithClass;
  SubscriberOfString: string;
begin
  SubscribeImplementedWithClass := SubscriberOf;
  MessageImplementedWithClass := Message;
  SubscriberOfString := SubscribeImplementedWithClass.ToString;
  MessageString := MessageImplementedWithClass.ToString; // wrong VMT here, Delphi XE SP2
  Logger.Log('Consume(SubscriberOf: %s, Message:%s);',
    [SubscriberOfString, MessageString]);
//    [SubscriberOf.ClassType.ClassName, Message.ClassType.ClassName]);
  inherited Consume(SubscriberOf, Message);
end;

end.

旧解决方案：

这可能可以解决问题，但我仍然觉得解决方案有点复杂。

MessageServiceUnit：ISubscriberOf现在具有GUID和Supports方法来检查是否实际支持IMessage。

unit MessageServiceUnit;

interface

uses
  Generics.Collections;

type
  IMessage = interface(IInterface)
    ['{B1794F44-F6EE-4E7B-849A-995F05897E1C}']
  end;

  ISubscriber = interface(IInterface)
    ['{D655967E-90C6-4613-92C5-1E5B53619EE0}']
  end;

  ISubscriberOf<T: IMessage> = interface(ISubscriber)
    ['{6FD82B1D-61C6-4572-BA7D-D70DA9A73285}']
    procedure Consume(const Message: T);
    function Supports(const Message: T): Boolean;
  end;

  TMessageService = class
  private
    FSubscribers: TList<ISubscriber>;
  public
    constructor Create;
    destructor Destroy; override;
    procedure SendMessage(const Message: IMessage);
    procedure Subscribe(const Subscriber: ISubscriber);
    procedure Unsubscribe(const Subscriber: ISubscriber);
  end;

implementation

uses
  SysUtils;

constructor TMessageService.Create;
begin
  inherited Create();
end;

destructor TMessageService.Destroy;
begin
  inherited Destroy();
end;

procedure TMessageService.SendMessage(const Message: IMessage);
var
  lSubscriber: ISubscriber;
  lSubscriberOf: ISubscriberOf<IMessage>;
begin
  for lSubscriber in FSubscribers do
  begin
    if Supports(lSubscriber, ISubscriberOf<IMessage>, lSubscriberOf) then
      if lSubscriberOf.Supports(Message) then
        lSubscriberOf.Consume(Message);
  end;
end;

procedure TMessageService.Subscribe(const Subscriber: ISubscriber);
begin
  FSubscribers.Add(Subscriber);
end;

procedure TMessageService.Unsubscribe(const Subscriber: ISubscriber);
begin
  FSubscribers.Remove(Subscriber);
end;

end.

MessagesUnit: 每个消息都有一个带有GUID的interface，以便Supports可以检查GUID。

unit MessagesUnit;

interface

uses
  MessageServiceUnit;

type
  IMyMessage = interface(IMessage)
    ['{84B42EC8-CAC0-44B4-97A8-05AE5B636236}']
  end;
  TMyMessage = class(TInterfacedObject, IMessage, IMyMessage);

  IMyOtherMessage = interface(IMessage)
    ['{AB323765-FF7B-4852-91AA-B7ECC1845B41}']
  end;
  TMyOtherMessage = class(TInterfacedObject, IMessage, IMyOtherMessage);

implementation

end.

MessageSubscribersUnit: 所有的订阅者都有一个Supports方法，用于检查正确的GUID。

unit MessageSubscribersUnit;

interface

uses
  MessagesUnit, MessageServiceUnit;

type
  TMySubscriber = class(TInterfacedObject, ISubscriberOf<IMyMessage>)
    procedure Consume(const Message: IMyMessage);
    function Supports(const Message: IMyMessage): Boolean;
  end;

  TMyOtherSubscriber = class(TInterfacedObject, ISubscriberOf<IMyOtherMessage>)
    procedure Consume(const Message: IMyOtherMessage);
    function Supports(const Message: IMyOtherMessage): Boolean;
  end;

implementation

uses
  SysUtils;

procedure TMySubscriber.Consume(const Message: IMyMessage);
begin
  //
end;

function TMySubscriber.Supports(const Message: IMyMessage): Boolean;
begin
  Result := SysUtils.Supports(Message,  IMyMessage);
end;

procedure TMyOtherSubscriber.Consume(const Message: IMyOtherMessage);
begin
  //
end;

function TMyOtherSubscriber.Supports(const Message: IMyOtherMessage): Boolean;
begin
  Result := SysUtils.Supports(Message,  IMyOtherMessage);
end;

end.

MessagesUnit: 包含具体的消息（包括接口和类类型），其中包含IID GUID以使它们与Supports区分开来。

unit MessagesUnit;

interface

uses
  MessageServiceUnit,
  ClassicMessageSubscriberUnit;

type
  IMyMessage = interface(IMessage)
    ['{84B42EC8-CAC0-44B4-97A8-05AE5B636236}']
  end;
  TMyMessage = class(TInterfacedObject, IMessage, IMyMessage);

  IMyOtherMessage = interface(IMessage)
    ['{AB323765-FF7B-4852-91AA-B7ECC1845B41}']
  end;
  TMyOtherMessage = class(TInterfacedObject, IMessage, IMyOtherMessage);

implementation

end.

MessageSubscribersUnit：包含特定的订阅者（接口和类类型），它们现在不再需要 Supports 方法：它们只包含 Consume 方法。

unit MessageSubscribersUnit;

interface

uses
  MessagesUnit,
  MessageServiceUnit,
  GenericSubscriberOfUnit,
  ClassicMessageSubscriberUnit;

type
  TMySubscriber = class(TSupporterOf<IMyMessage>, ISubscriber, ISubscriberOf<IMyMessage>)
    procedure Consume(const Message: IMyMessage);
  end;

  TMyOtherSubscriber = class(TSupporterOf<IMyOtherMessage>, ISubscriber, ISubscriberOf<IMyOtherMessage>)
    procedure Consume(const Message: IMyOtherMessage);
  end;

implementation

uses
  SysUtils;

procedure TMySubscriber.Consume(const Message: IMyMessage);
begin
  //
end;

procedure TMyOtherSubscriber.Consume(const Message: IMyOtherMessage);
begin
  //
end;

end.

--jeroen

做到了，谢谢！我本来希望有一种方法可以避免每个消息都需要两种方法和一个接口，但我认为这是不可能的。 - Erick Sasse
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