03.Delphi通过接口实现多重继承的优化

在上一篇02中，写到的sayhello函数，需要使用2个接口参数，很繁琐。可以使用as参数，把多重继承的子类对象变成需要的对象

uSayHello代码如下

unit uSayHello;

interface

type
  // 接口
  IGreetable = interface
    ['{D91DDE09-0FC4-4FE9-AE0D-9877E2F73BF6}']
    // 输出函数
    function SayHello: string;
  end;

  // TInterfacedObject实现了接口的默认方法
  TMan = class(TInterfacedObject)
    // 语言，姓名，皮肤颜色 属性
    Language: string;
    Name: string;
    SkinColor: string;
  public
    // 虚方法virtual, 子类需要使用override来覆盖
    constructor create; virtual;
  end;

  // 通过接口，继承了TMan的Create同时也继承了TGreetable的SayHello
  TChinese = class(TMan, IGreetable)
  public
    constructor create; override;
  private
    function SayHello: string;
  end;

  TAmerican = class(TMan, IGreetable)
  public
    constructor create; override;
  private
    function SayHello: string;
  end;

  TFrench = class(TMan, IGreetable)
  public
    constructor create; override;
  private
    function SayHello: string;
  end;

  TKorean = class(TMan, IGreetable)
  public
    constructor create; override;
  private
    function SayHello: string;
  end;

implementation

constructor TMan.create;
begin
  Name := '张三';
  Language := '中文';
  SkinColor := '黄色';
end;

constructor TChinese.create;
begin
  inherited;
end;

constructor TAmerican.create;
begin
  Name := 'Lee';
  Language := '英文';
  SkinColor := '黑色';
end;

constructor TFrench.create;
begin
  Name := '苏菲';
  Language := '法文';
  SkinColor := '白色';
end;

constructor TKorean.create;
begin
  Name := '金知中';
  Language := '韩文';
  SkinColor := '黄色';
end;

function TChinese.SayHello;
begin
  Result := 'chinese.bmp';
end;

function TAmerican.SayHello;
begin
  Result := 'American.bmp';
end;

function TFrench.SayHello;
begin
  Result := 'French.bmp';
end;

function TKorean.SayHello;
begin
  Result := 'Korean.bmp';
end;

end.

ufrmSayHello代码如下

unit ufrmSayHello;

interface

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

type
  TfrmSayHello = class(TForm)
    GroupBox1: TGroupBox;
    edtName: TLabeledEdit;
    edtSkinColor: TLabeledEdit;
    edtLanguage: TLabeledEdit;
    btnUSA: TButton;
    btnKorean: TButton;
    btnCN: TButton;
    btnFrench: TButton;
    Image1: TImage;
    procedure btnUSAClick(Sender: TObject);
    procedure btnCNClick(Sender: TObject);
    procedure btnFrenchClick(Sender: TObject);
    procedure btnKoreanClick(Sender: TObject);

  private
    procedure sayhello(AMan: TMan);
  public
    { Public declarations }
  end;

var
  frmSayHello: TfrmSayHello;

implementation

{$R *.dfm}

// 多个不同参数的函数，集成到了一个
procedure TfrmSayHello.sayhello(AMan: TMan);
var
  G: IGreetable;
begin
  // 类实现的多态
  edtName.Text := AMan.Name;
  edtLanguage.Text := AMan.Language;
  edtSkinColor.Text := AMan.SkinColor;
  // as把某个类型对象转换成所需要的类型。 is是判断某对象是否是某类型。
  G := AMan as IGreetable;
  // 接口实现的多态
  Image1.Picture.LoadFromFile(G.sayhello);
end;

procedure TfrmSayHello.btnUSAClick(Sender: TObject);
begin
  // sayhello参数定义的父内，传入时传的子类，
  sayhello(TAmerican.create);
end;

procedure TfrmSayHello.btnCNClick(Sender: TObject);
begin
  sayhello(TChinese.create);
end;

procedure TfrmSayHello.btnFrenchClick(Sender: TObject);
begin
  sayhello(TFrench.create);
end;

procedure TfrmSayHello.btnKoreanClick(Sender: TObject);
begin
  sayhello(TKorean.create);
end;

end.