Delphi:如何将类移出单元；避免循环引用

Question

Question: i want to split two classes out to their own file, while avoiding circular references.

我有一个包含一些类(以及一些枚举和常量)的单元。任何人都会认出Click and Clack the tappet brothers :

unit Cartalk;

interface

type
   TSolution = (solTransmission, solBrakes, solGremlins);

   TTappetBrother = class(TObject)
   public
      function GetSolution: TSolution; virtual; abstract;
   end;

   TClick = class(TTappetBrother)
   public      
      function GetSolution: TSolution; override;
   end;

   TClack = class(TTapperBrother)
   public
      function GetSolution: TSolution; override;
   end;

implementation

function TClick.GetSolution: TSolution;
begin
   Result := solTransmission;
end;

function TClack.GetSoltution: TSolution;
begin
   Result := solGremlins;
end;

end.

现在显然我的两个类 TClick 和 TClick 非常复杂。为了便于管理，我想将 TClick 和 TClack 拆分为它们自己的单元同时不破坏任何现有的外部代码.

我的第一个尝试是:

unit Cartalk;

interface

uses
   Cartalk_Click, Cartalk_Clack;

type
   TSolution = (solTransmission, solBrakes, solGremlins);

   TTappetBrother = class(TObject)
   public
      function GetSolution: TSolution; virtual; abstract;
   end;

   TClick = Cartalk_Click.TClick; //alias brought in from Cartalk_Click.pas

   TClack = Cartalk_Clack.TClack; //alias brought in from Cartalk_Clack.pas

 implementation

 end.

完美，我在 Cartalk.pas 中拥有所有相同的类，现在我只需编写 Cartalk_Click.pas 和 Cartalk_Clack.pas >:

unit Cartalk_Click;

interface

type
   TClick = class(TTappetBrother)
   public      
      function GetSolution: TSolution; override;
   end;

implementation

function TClick.GetSolution: TSolution;
begin
   Result := solTransmission;
end;

end.

问题当然是 TTappetBrother 和 TSolution 没有在此单元中声明。因此，我们在用途中添加对它们居住位置的引用，观察它的失败，并触及我问题的核心:

unit Cartalk_Click;

interface

uses
   Cartalk;

type
   TClick = class(TTappetBrother)
   public      
      function GetSolution: TSolution; override;
   end;

implementation

function TClick.GetSolution: TSolution;
begin
   Result := solTransmission;
end;

end.

现在 Cartalk 和 Cartalk_Click 之间存在循环引用。

注意:当然，我没有 Cartalk 装置，还有 Click 和 Clack the tapper brothers - 这只是一个例子。实际上，我的单​​元中有 3 个类、20 个枚举和 293 个常量。

Answer 1

写一个单位:

unit Tappet;

interface

type
   TSolution = (solTransmission, solBrakes, solGremlins);

   TTappetBrother = class(TObject)
   public
      function GetSolution: TSolution; virtual; abstract;
   end;

implementation

end.

并在Click 和Clack 单元中使用它。然后编写 CarTalk 单元以使用所有这三个并在其接口(interface)中导出所需的类型。不需要循环引用。