Delphi：如何向后代添加不同的构造函数？ [英] Delphi: How to add a different constructor to a descendant?

问题描述

更新：我原来的例子很复杂。这里有一个简单的8行示例，解释一个代码块中的所有内容。以下不会编译发出警告：

  TComputer = class（TObject）
 public 
 constructor Create（Cup：Integer）;虚拟; 
 end; 
 
 TCellPhone = class（TComputer）
 public 
构造函数Create（Cup：Integer; Teapot：string）;虚拟; 
 end; 
  

注意：这个问题是我正在进行的一系列问题的第3部分Delphi中构造函数的细节

原始问题

如何向现有类添加构造函数？

让我们给出一个假设的例子（例如，我在SO编辑器中输入的一个例子，因此它可能或可能无法编译）：

  TXHTMLStream = class（TXMLStream）
 public 
 ... 
 end;进一步假设正常使用 TXHTMLStream   
 
涉及在可以使用之前执行大量重复的代码：
  var 
 xs：TXHTMLStream; 
 begin 
 xs：= TXHTMLStream.Create（filename）; 
 xs.Encoding：= UTF32; 
 xs.XmlVersion：= 1.1; 
 xs.DocType：='strict'; 
 xs.PreserveWhitespace：='true'; 
 ... 
 
 xs.Save（xhtmlDocument）; 
  
假设我想创建一个简化所有样板设置代码的构造函数：
  TXHTMLStream = class（TXMLStream）
 public 
构造函数Create（filename：string; Encoding：TEncoding）;虚拟; 
 end; 
 
构造函数TXHTMLStream.Create（filename：string; Encoding：TEncoding）; 
 begin 
 inherited Create（filename）; 
 xs.Encoding：= Encoding; 
 xs.XmlVersion：= 1.1; 
 xs.DocType：='strict'; 
 xs.PreserveWhitespace：= True; 
 ... 
 end; 
  
这简化了对象的使用：
  var 
 xs：TXHTMLStream; 
 begin 
 xs：= TXHTMLStream.Create（filename，UTF32）; 
 xs.Save（xhtmlDocument）; 
  
除了现在Delphi抱怨我的新构造函数隐藏了旧的构造函数。 
 
 
方法创建隐藏基本类型TXMLStream的虚拟方法
 
 
我当然没有   隐藏祖先create  -  i   
 
 
 
如何将一个构造函数（具有不同签名）添加到后代类，同时保留祖先构造函数，  
我的直接反应是使用 overload 关键字，如：
  TCellPhone = class（TComputer）
 public 
 constructor Create（Cup：Integer;茶壶：串）;再引入超载;虚拟; 
 end; 
 
 编辑：感谢Ian的编辑，我的答案。我想认为我是勇敢的，所以我将提供一个更完整的例子：
 程序Project1; 
 
 {$ APPTYPE CONSOLE} 
 
使用
 SysUtils; 
 
 type 
 
 TComputer = class（TObject）
 public 
构造函数Create（Cup：Integer）;虚拟; 
 end; 
 
 TCellPhone = class（TComputer）
 public 
构造函数Create（Cup：Integer; Teapot：string）;再引入超载;虚拟; 
 end; 
 
 {TComputer} 
 
构造函数TComputer.Create（Cup：Integer）; 
 begin 
 writeln（'constructed computer：cup ='，Cup）; 
 end; 
 
 {TCellPhone} 
 
构造函数TCellPhone.Create（Cup：Integer; Teapot：string）; 
 begin 
 inherited创建（Cup）; 
 writeln（'constructed cellphone：Teapot ='，Teapot）; 
 end; 
 
 var 
 C1，C2，C3：TComputer; 
 
 begin 
 C1：= TComputer.Create（1）; 
 Writeln; 
 C2：= TCellPhone.Create（2）; 
 Writeln; 
 C3：= TCellPhone.Create（3，'kettle'）; 
 Readln; 
 end。 
  
，结果是：
 建造的电脑：cup = 1 
 
建造的电脑：cup = 2 
 
建造的电脑：cup = 3 
手机：茶壶= kettle 
  
 
Update: The example i originally had was kind of complex. Here's a simple 8 line example that explains everything in one code block. The following does not compile gives a warning:
TComputer = class(TObject)
public
    constructor Create(Cup: Integer); virtual;
end;

TCellPhone = class(TComputer)
public
    constructor Create(Cup: Integer; Teapot: string); virtual;
end;
Note: This question is part 3 in my ongoing series of questions about the subtlties of constructors in Delphi


Original question

How can i add a constructor to an existing class? 

Let's give an hypothetical example (i.e. one that i'm typing up in here in the SO editor so it may or may not compile):
TXHTMLStream = class(TXMLStream)
public
   ...
end;
Further assume that the normal use of TXHTMLStream involved performing a lot of repeated code before it can be used:
var
   xs: TXHTMLStream;
begin
   xs := TXHTMLStream.Create(filename);
   xs.Encoding := UTF32;
   xs.XmlVersion := 1.1;
   xs.DocType := 'strict';
   xs.PreserveWhitespace := 'true';
   ...

   xs.Save(xhtmlDocument);
Assume that i want to create a constructor that simplifies all that boilerplate setup code:
TXHTMLStream = class(TXMLStream)
public
    constructor Create(filename: string; Encoding: TEncoding); virtual;
end;

constructor TXHTMLStream.Create(filename: string; Encoding: TEncoding);
begin
   inherited Create(filename);
   xs.Encoding := Encoding;
   xs.XmlVersion := 1.1;
   xs.DocType := 'strict';
   xs.PreserveWhitespace := True;
   ...
end;
That simplifies usage of the object to:
var
   xs: TXHTMLStream;
begin
   xs := TXHTMLStream.Create(filename, UTF32);
   xs.Save(xhtmlDocument);
Except now Delphi complains that my new constructor hides the old constructor. 

  
Method 'Create' hides virtual method of base type 'TXMLStream'
i certainly didn't mean to hide the ancestor create - i want both.

How do i add a constructor (with a different signature) to a descendant class, while keeping the ancestor constructor so it can still be used?
解决方案
My immediate reaction is to use the overload keyword, as in:
TCellPhone = class(TComputer)
public
    constructor Create(Cup: Integer; Teapot: string); reintroduce; overload; virtual;
end;
Edit: Thanks Ian for the edit, which makes an answer out of my answer. I would like to think that I got it for bravery, so I am going to contribute a fuller example:
program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type

TComputer = class(TObject)
public
    constructor Create(Cup: Integer); virtual;
end;

TCellPhone = class(TComputer)
public
    constructor Create(Cup: Integer; Teapot: string); reintroduce; overload; virtual;
end;

{ TComputer }

constructor TComputer.Create(Cup: Integer);
begin
  writeln('constructed computer: cup = ', Cup);
end;

{ TCellPhone }

constructor TCellPhone.Create(Cup: Integer; Teapot: string);
begin
  inherited Create(Cup);
  writeln('constructed cellphone: Teapot = ', Teapot);
end;

var
  C1, C2, C3: TComputer;

begin
  C1 := TComputer.Create(1);
  Writeln;
  C2 := TCellPhone.Create(2);
  Writeln;
  C3 := TCellPhone.Create(3, 'kettle');
  Readln;
end.
with the result being:
constructed computer: cup = 1

constructed computer: cup = 2

constructed computer: cup = 3
constructed cellphone: Teapot = kettle


                        
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