Delphi語言學習8-類成員（字段和方法）

1.Class Fields

//例1 成員變量
type
   TAncestor = class
      Value: Integer;
   end;
   TDescendant = class(TAncestor)
      Value: string;    // hides the inherited Value field
   end;
var
   MyObject: TAncestor;
begin
   MyObject := TDescendant.Create;
   MyObject.Value := 'Hello!'     // error
  (MyObject as TDescendant).Value := 'Hello!'   // works!
end;
//例2 靜態字段
type
    TMyClass = class
      public
        class var        // Introduce a block of class static fields.
          Red: Integer;
          Green: Integer;
          Blue: Integer;
        var              // Ends the class var block.
          InstanceField: Integer;
    end;
//靜態字段可以單獨調用
TMyClass.Red := 1;
TMyClass.Green := 2;
TMyClass.Blue := 3;
//靜態字段也可以通過對象實例調用
var
    myObject: TMyClass;
myObject.Red := 1;
myObject.Green := 2;
myObject.Blue := 3;

2.Method Binding

//Static Methods
//例1
type
    TFigure = class
      procedure Draw;
    end;
    TRectangle = class(TFigure)
      procedure Draw;
    end;
var
    Figure: TFigure;
    Rectangle: TRectangle;
    begin
            Figure := TFigure.Create;
            Figure.Draw;              // calls TFigure.Draw
            Figure.Destroy;
            Figure := TRectangle.Create;
            Figure.Draw;              // calls TFigure.Draw
            TRectangle(Figure).Draw;  // calls TRectangle.Draw
            Figure.Destroy;
            Rectangle := TRectangle.Create;
            Rectangle.Draw;          // calls TRectangle.Draw
            Rectangle.Destroy;
    end;
//虛方法和動態方法
type
    TFigure = class
      procedure Draw; virtual;
    end;
    TRectangle = class(TFigure)
      procedure Draw; override;
    end;
    TEllipse = class(TFigure)
      procedure Draw; override;
    end;
var
   Figure: TFigure;
    begin
     Figure := TRectangle.Create;
     Figure.Draw;      // calls TRectangle.Draw
     Figure.Destroy;
     Figure := TEllipse.Create;
     Figure.Draw;      // calls TEllipse.Draw
     Figure.Destroy;
   end;
//例2
type
   T1 = class(TObject)
      procedure Act; virtual;
   end;
   T2 = class(T1)
      procedure Act;   // Act is redeclared, but not overridden
   end;
var
   SomeObject: T1;
begin
   SomeObject := T2.Create;
   SomeObject.Act;    // calls T1.Act
end;
//類方法 Class Method
//Ordinary Class Methods
//The definition of a class method must begin with the reserved word class. For example,
type
  TFigure = class
  public
     class function Supports(Operation: string): Boolean; virtual;
     class procedure GetInfo(var Info: TFigureInfo); virtual;
  end;
//The defining declaration of a class method must also begin with class. For example,
class procedure TFigure.GetInfo(var Info: TFigureInfo);
begin
end;
//Class Static Methods
type
   TMyClass = class
     strict private
       class var
       FX: Integer;
     strict protected
       // Note: accessors for class properties must be declared class static.
       class function GetX: Integer; static;
       class procedure SetX(val: Integer); static;
     public
       class property X: Integer read GetX write SetX;
       class procedure StatProc(s: String); static;
   end;
//調用
TMyClass.X := 17;
TMyClass.StatProc('Hello');

3.函數重載

type
  T1 = class(TObject)
    procedure Test(I: Integer); overload; virtual;
  end;
  T2 = class(T1)
    procedure Test(S: string); reintroduce; overload;
  end;
SomeObject := T2.Create;
SomeObject.Test('Hello!');       // calls T2.Test
SomeObject.Test(7);              // calls T1.Test

4 構造函數

type
   TShape = class(TGraphicControl)
     private
       FPen: TPen;
       FBrush: TBrush;
       procedure PenChanged(Sender: TObject);
       procedure BrushChanged(Sender: TObject);
     public
       constructor Create(Owner: TComponent); override;
       destructor Destroy; override;
   end;
constructor TShape.Create(Owner: TComponent);
begin
    inherited Create(Owner);     // Initialize inherited parts
    Width := 65;          // Change inherited properties
    Height := 65;
    FPen := TPen.Create;  // Initialize new fields
    FPen.OnChange := PenChanged;
    FBrush := TBrush.Create;
    FBrush.OnChange := BrushChanged;
end;