物件 : 繼承性(二)

1. unit1有Tc1及Tc2類別，Tc2類別是繼承Tc1，因屬同一個unit底下，所以所有的屬性(public、private及protected)皆可以被呼叫。

2. unit2若單純uses unit1的話，Tc1類別的public，Tc2類別的public，及Tc類別所繼承父的public。

3. unit2有Tc3類別，其為繼承Tc2，則只能呼叫public及protected，但是不能呼叫private。在此須注意uses要放在interface裡，不能放在implementation裡。

uint1.pas

unit Unit1;
interface
uses
   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
   Dialogs, StdCtrls;
type
   TForm1 = class(TForm)
   procedure FormCreate(Sender: TObject);
   private
   { Private declarations }
   public
   { Public declarations }
end;
type
   Tc1 = class
   public
     public_c1: string;
   private
     private_c1: string;
   protected
     protected_c1: string;
end;
type
   Tc2 = class(Tc1)
   public
     public_c2: string;
   private
     private_c2: string;
   protected
     protected_c2: string;
end;
var
   Form1: TForm1;
   c2: Tc2;
   c1: Tc1;
implementation
uses Unit2;
{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
   c2 := Tc2.Create;
   c2.public_c2:='a';
   c2.private_c2:='b';
   c2.protected_c2:='c';
   c2.public_c1:='d';  //都可以存取，主要是繼承Tc1
   c2.private_c1:='e';
   c2.protected_c1:='f';
   c1 := Tc1.Create;
   c1.public_c1:='aa';
   c1.private_c1:='bb';
   c1.protected_c1:='cc';
 // 各位要觀察的是 c2或c1物件按下.的時候可以下拉哪些 function
end;

end.

uint2.pas

unit Unit2;
interface
uses
   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
   Dialogs, StdCtrls, unit1;

//因為要繼承 Tc2，所以引用的 unit1 單元須寫在 class type的宣告之前，所以須
//寫在 interface 區
type
   TForm2 = class(TForm)
     Button1: TButton;
     Button2: TButton;
     procedure Button1Click(Sender: TObject);
     procedure Button2Click(Sender: TObject);
   private
     { Private declarations }
   public
     { Public declarations }
end;
type
   Tc3= class(Tc2)  //因為在interface 就需要Tc2，所以unit1要寫在interface上面喔
   public
     public_c3: string;
   private
     private_c3: string;
   protected
     protected_c3: string;
end;
var
   Form2: TForm2;
implementation
//uses Unit1;   //不能寫implemetation後面
{$R *.dfm}
procedure TForm2.Button1Click(Sender: TObject);
begin
 // 只有 public 區的資料可以被讀取
   c1.public_c1:='a';
   c2.public_c1 :='b';
   c2.public_c2 := 'c';
end;
procedure TForm2.Button2Click(Sender: TObject);
 var c3: Tc3;
begin
   c3:= Tc3.Create;
   c3.public_c3 := 'a';
   c3.private_c3:= 'a';
   c3.protected_c3:= 'a';

   c3.public_c2:= 'a';
   c3.protected_c2:= 'a';

   c3.public_c1 := 'a';
   c3.protected_c1:= 'a';
// 有沒有發現Tc2及Tc1內的private變數無法經由繼承的方式來讀取，
// 但是protected 的資料卻可存取
// 記得如果是Tc2與Tc3在同一個 unit，則 private 變數仍可存取

end;
end.

有繼承的類別，若有與父類別相同的程序(屬性)則將會覆蓋掉父類別的程序(屬性)

unit Unit1;
interface
uses
   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
   Dialogs, StdCtrls;
type
   TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
   private
   { Private declarations }
   public
   { Public declarations }
end;
type
   Tc1 = class
   public
     public_c1: string;
     procedure public_p1;
   private
     private_c1: string;
   protected
     protected_c1: string;
end;
type
   Tc2 = class(Tc1)
   public
     public_c2: string;
     procedure public_p1;
     procedure public_p2;
   private
     private_c2: string;
   protected
     protected_c2: string;
end;
var
   Form1: TForm1;
   c2: Tc2;
   c1: Tc1;
implementation
uses Unit2;
{$R *.dfm}
procedure Tc1.public_p1;
begin
  showmessage('Tc1.p1');
end;

procedure Tc2.public_p1;
begin
  showmessage('Tc2.p1');
end;

procedure Tc2.public_p2;
begin
  showmessage('Tc2.p2');
end;

procedure TForm1.Button1Click(Sender: TObject);
var c1:Tc1;
    c2:Tc2;
begin
  c1:=Tc1.create;
  c2:=Tc2.Create;
  c1.public_p1; //Tc1.p1
  c2.public_p1; //Tc2.p1   有相同的子類別會覆蓋掉父類別的程序(屬性)
  c2.public_p2; //Tc2.p2
end;

end.