生成TStringList派生类的有关问题（待）

生成TStringList派生类的问题（在线等待）
Ta =Class(TStringList)
private

public
constructor Create(n:integer);
destructor Destroy;override;
end;
implementation
constructor Ta.Create(n:Integer);
begin
inherited create;
self.SetCapacity(n);
end;

destructor Ta.Destroy;
begin
end;

为什么总是报地址访问错误？

------解决方案--------------------
给你看看我写的，和你的是一样的，在我这是不会报错的！共同学习吧！

{------------------------------------------
TMyStringList类定义单元
-------------------------------------------}
unit uMyStringList;

interface

uses Classes;

type
TMyStringList = class(TStringList)
public
constructor Create(n: Integer);
destructor Destroy(); override;
end;

implementation

{ TMyStringList }

constructor TMyStringList.Create(n: Integer);
begin
inherited Create;
Self.SetCapacity(n);
end;

destructor TMyStringList.Destroy;
begin
inherited;
end;

end.

{------------------------------------------
TMyStringList类使用
-------------------------------------------}
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, uMyStringList;

type
TForm1 = class(TForm)
Button1: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
sl: TMyStringList;
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
i: Integer;
begin
for i := 0 to sl.Count - 1 do
begin
Self.Caption := Self.Caption + sl[i];
end;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
i: Integer;
begin
sl := TMyStringList.Create(10);
for i := 0 to 10 do
begin
sl.Add(IntToStr(i));
end;
end;

end.

------解决方案--------------------

Delphi(Pascal) code

type
  Ta =Class(TStringList)
  public
    constructor Create(n:integer); reintroduce;
    destructor Destroy; override;
  end;

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  with ta.Create(6) do
  try
    Add('This is a beautiful world!');

    Caption := Text;
  finally
    Free;
  end;
end;

{ Ta }

constructor Ta.Create(n: integer);
begin
  inherited Create();
  SetCapacity(n);
end;

destructor Ta.Destroy;
begin
  inherited;
end;

------解决方案--------------------
with ta.Create(6) do
  try
  Add('This is a beautiful world!');
  Caption := Text;
  finally
  Free;
  end;
这样写没有问题的，with ta.Create(6) do 一句已经实例化 Ta 了,所有下面的Try finally end 块可以操作...

------解决方案--------------------
7楼代码等效于9楼代码

这就是 with * do的作用

楼主的不想每次用都实例化，且应用中里需要一个这样的列表 可以用单实例模型

Delphi(Pascal) code


 Ta =Class(TStringList) 
    private 

    public 
    constructor Create(n:integer); 
    destructor Destroy;override; 
  end; 
implementation 
constructor Ta.Create(n:Integer); 
begin 
  inherited create; 
  self.SetCapacity(n); 
end; 

destructor Ta.Destroy; 
begin 
end; 

// 注意以下代码
function MyTa(n: Integer): Ta;

var
  _VAR_LIST: Ta = nil;

function MyTa(n: Integer): Ta;
begin
  if Not Assigned(_VAR_LIST) then
  _VAR_LSIT = Ta.Create(n)
  else
  _VAR_LIST.SetCapacity(n); 

  Result := _VAR_LIST;  
end;


使用时直接用就行了
MyTa(100);

生成TStringList派生类的有关问题（待）

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