现在准备一步步地模拟 TList 类, 建立一个自己的 TMyList.
首先, 这个类中应该包括前面提到的那个 Pointer 数组(TPointerList)的指针(PPointerList):
TMyList = class(TObject)
FList: PPointerList;
end;
既然是一个列表, 应该有 Count 字段:
TMyList = class(TObject)
FList: PPointerList;
FCount: Integer;
end;
TList 类还有一个 FCapacity 字段.
譬如当前列表中有 10 个元素时, 其实列表已经提前申请出更多位置, 这样就不必每次添加每次申请内存, 从而提高了效率.
这个 FCapacity 字段就表示已申请的可放置元素位置的总数.
TMyList = class(TObject)
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
end;
它们都应该是私有的:
TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
public
end;
应该用属性操作它们:
unit Unit1; interface uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs; type
TForm1 = class(TForm)
end;
{--------------------------------}
TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
public
property Capacity: Integer; {光标放在属性上, 执行 Shift+Ctrl+C, 自动建立属性}
property Count: Integer;
property List: PPointerList;
end;
{--------------------------------} var
Form1: TForm1; implementation {$R *.dfm} end.
自动建立后的属性:
unit Unit1; interface uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs; type
TForm1 = class(TForm)
end;
{--------------------------------}
TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
procedure SetCapacity(const Value: Integer);
procedure SetCount(const Value: Integer);
procedure SetList(const Value: PPointerList);
public
property Capacity: Integer read FCapacity write SetCapacity;
property Count: Integer read FCount write SetCount;
property List: PPointerList read FList write SetList;
end;
{--------------------------------} var
Form1: TForm1; implementation {$R *.dfm} { TMyList } procedure TMyList.SetCapacity(const Value: Integer);
begin
FCapacity := Value;
end; procedure TMyList.SetCount(const Value: Integer);
begin
FCount := Value;
end; procedure TMyList.SetList(const Value: PPointerList);
begin
FList := Value;
end; end.
在 TList 中, SetCount 和 SetCapacity 方法都是放在 protected 区以供子类使用, 这里暂时不考虑继承的问题, 就让它们先在 private 区吧;
不过 List 属性应该是只读的, 它就是那个核心数组的指针, 对它的赋值应该通过更多其他的方法.
修改如下:
unit Unit1; interface uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs; type
TForm1 = class(TForm)
end;
{--------------------------------}
TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
procedure SetCapacity(const Value: Integer);
procedure SetCount(const Value: Integer);
public
property Capacity: Integer read FCapacity write SetCapacity;
property Count: Integer read FCount write SetCount;
property List: PPointerList read FList;
end;
{--------------------------------} var
Form1: TForm1; implementation {$R *.dfm} { TMyList } procedure TMyList.SetCapacity(const Value: Integer);
begin
FCapacity := Value;
end; procedure TMyList.SetCount(const Value: Integer);
begin
FCount := Value;
end; end.
作为一个列表, 最起码应该有 Add、Delete、Clear 方法.
Add 方法的参数应该是一个指针(TList 就是存放指针的吗), 如果需要同时返回元素的位置, 应该定义成函数;
Delete 是删除指定位置上的元素, 参数是个位置号;
Clear 是清除列表, 对象释放(Destroy)时也应该执行此过程.
综上所述, 修改如下:
unit Unit1; interface uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs; type
TForm1 = class(TForm)
end;
{--------------------------------}
TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
procedure SetCapacity(const Value: Integer);
procedure SetCount(const Value: Integer);
public
destructor Destroy; override; {覆盖父类的 Destroy 方法}
function Add(Item: Pointer): Integer;
procedure Clear; {在 TList 中这是个虚方法, 以备子类覆盖}
procedure Delete(Index: Integer);
property Capacity: Integer read FCapacity write SetCapacity;
property Count: Integer read FCount write SetCount;
property List: PPointerList read FList;
end;
{--------------------------------} var
Form1: TForm1; implementation {$R *.dfm} { TMyList } function TMyList.Add(Item: Pointer): Integer;
begin end; procedure TMyList.Clear;
begin end; procedure TMyList.Delete(Index: Integer);
begin end; destructor TMyList.Destroy;
begin
Clear; {在类释放时同时清除列表}
inherited; {在 TList 中没有这句, 大概是因为它的父类也没什么可继承的}
end; procedure TMyList.SetCapacity(const Value: Integer);
begin
FCapacity := Value;
end; procedure TMyList.SetCount(const Value: Integer);
begin
FCount := Value;
end; end.
为了让代码更清晰, 还是把这个类相关的所有代码放到一个独立的单元吧(新建一个单元, 我们把它保存为: MyList.pas).
因为 MaxListSize、TPointerList、PPointerList 都是在 Classes 单元定义的, 为了省略 uses Classes, 在 MyList 单元中重新做了定义.
unit MyList; interface const
MaxListSize = Maxint div ; type
PPointerList = ^TPointerList;
TPointerList = array[..MaxListSize - ] of Pointer; TMyList = class(TObject)
private
FList: PPointerList;
FCount: Integer;
FCapacity: Integer;
procedure SetCapacity(const Value: Integer);
procedure SetCount(const Value: Integer);
public
destructor Destroy; override;
function Add(Item: Pointer): Integer;
procedure Clear;
procedure Delete(Index: Integer);
property Capacity: Integer read FCapacity write SetCapacity;
property Count: Integer read FCount write SetCount;
property List: PPointerList read FList;
end; implementation { TMyList } function TMyList.Add(Item: Pointer): Integer;
begin end; procedure TMyList.Clear;
begin end; procedure TMyList.Delete(Index: Integer);
begin end; destructor TMyList.Destroy;
begin
Clear;
inherited;
end; procedure TMyList.SetCapacity(const Value: Integer);
begin end; procedure TMyList.SetCount(const Value: Integer);
begin end; end.
至此, 类的轮廓已经出来, 该实现一下这些方法了.