在TDictionary中使用继承接口作为键

Question

一个继承的接口能够作为TDictionary中的键吗？

//! Note the inheritance of the interfaces
ILoggingProvider = interface
  procedure Log(AMessage : string);
end;

IHTTPLoggingProvider = interface(ILoggingProvider)      
  function Login(AUserName : string; APassword : string) : boolean
end;

ILiveLoggingProvider = interface(ILoggingProvider)
  function ConnectMonitor : boolean
end;

var
  loggers : TDictionary<ILoggingProvider,TObject>;

...

loggers.add(ILoggingProvider, TSomeLogger.Create());
loggers.add(IHTTPLoggingProvider , TSuperLogger.Create()); //fails!
loggers.add(ILiveLoggingProvider , TAnotherLogger.Create()); //fails!


 ... //and the use them selectively

if loggers.ContainsKey(IHTTPLoggingProvider ) then
  loggers.Items[IHTTPLoggingProvider].Log('Good bye world!');

... //and like this

var

  theLogger : IHTTPLoggingProvider;

if loggers.ContainsKey(IHTTPLoggingProvider ) then
begin
  theLogger := IHTTPLoggingProvider(loggers.Items[IHTTPLoggingProvider]);
  if theLogger.Login('billy', 'bones') then
    theLogger.Log('some message');
end;

- MX4399

---

当然，TDictionary<ILoggingProvider,TObject>想要接口引用而不是接口。将TObject强制转换为IHTTPLoggingProvider非常可疑。值类型应该是一个接口。我认为应该将键设置为GUID。或者我理解错了吗？ - David Heffernan

@David：正确 - 使用接口也可以工作，并且在使用纯接口方法时更加一致 - 很不错的想法。 当我声明TLoggers = TDictionary＜TGUID，ILoggingProvider＞时，在构建“TLoggers”实例时会引发异常“无效类型转换”，而使用loggers：= TDictionary＜TGUID，ILoggingProvider＞.Create 则正常运行。 有什么想法吗？ - MX4399

我的答案中的代码编译、运行和操作都是正确的。 - David Heffernan

Answer 1

接着我的评论，这是我认为如何实现它的方法：

type
  ILoggingProvider = interface
    ['{30598F45-1230-4208-B1A5-E1D2DA8F6D40}']
    procedure Log(AMessage : string);
  end;

  IHTTPLoggingProvider = interface(ILoggingProvider)
    ['{CFA01514-AC44-4E30-971B-115986B37D26}']
    function Login(AUserName : string; APassword : string) : boolean;
  end;

  ILiveLoggingProvider = interface(ILoggingProvider)
    ['{6EA68BEF-8D78-4FDF-AACD-1D164A272758}']
    function ConnectMonitor : boolean;
  end;

  TLoggingProvider = class(TInterfacedObject, ILoggingProvider)
    procedure Log(AMessage : string);
  end;

  THTTPLoggingProvider = class(TInterfacedObject, ILoggingProvider, IHTTPLoggingProvider)
    procedure Log(AMessage : string);
    function Login(AUserName : string; APassword : string) : boolean;
  end;

  TLiveLoggingProvider = class(TInterfacedObject, ILoggingProvider, ILiveLoggingProvider)
    procedure Log(AMessage : string);
    function ConnectMonitor : boolean;
  end;

procedure Main;
var
  loggers : TDictionary<TGUID,ILoggingProvider>;
  theLogger : IHTTPLoggingProvider;
begin
  loggers := TDictionary<TGUID,ILoggingProvider>.Create;
  try
    loggers.add(ILoggingProvider, TLoggingProvider.Create);
    loggers.add(IHTTPLoggingProvider, THTTPLoggingProvider.Create);
    loggers.add(ILiveLoggingProvider, TLiveLoggingProvider.Create);

    if loggers.ContainsKey(IHTTPLoggingProvider) then
      loggers.Items[IHTTPLoggingProvider].Log('Good bye world!');

    if loggers.ContainsKey(IHTTPLoggingProvider) then
    begin
      theLogger := loggers.Items[IHTTPLoggingProvider] as IHTTPLoggingProvider;
      if theLogger.Login('billy', 'bones') then
        theLogger.Log('some message');
    end;
  finally
    loggers.Free;
  end;
end;

- David Heffernan