有关组件创建时默认值
unit Unit1;

interface

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

Type
TcyEdit = Class(TEdit)
private
fIsBol: Boolean;
published
property IsBol: Boolean Read fIsBol Write fIsBol Default True;
end;

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

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
cyEdit: TcyEdit;
begin
cyEdit := TcyEdit.Create(Self);
cyEdit.Parent := Form1;
// cyEdit.IsBol := true; 在设计时不能进行设置么?

if cyEdit.fIsBol then
ShowMessage( 'Yes ')
else
ShowMessage( 'No ');

if cyEdit.IsBol then
ShowMessage( 'Yes ')
else
ShowMessage( 'No ');
end;

end.

1、cyEdit的值永远为false
2、设计时不能进行定义么？


[解决办法]
你的TcyEdit类的属性IsBol的所谓默认值True，只是在Published部分进行了申明，而TcyEdit类的构造函数，却仍然用的是其父类TEdit的构造函数，TEdit没有IsBol这个属性，所以...

你需要覆盖父类的构造函数，并在构造时，对属性进行赋值。如下：

unit Unit1;

interface

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

Type
TcyEdit = Class(TEdit)
private
fIsBol: Boolean;
public
constructor Create(AOwer : TComponent);override;//覆盖父类的构造方法
published
property IsBol: Boolean Read fIsBol Write fIsBol Default True;

end;

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

var
Form1: TForm1;

implementation

{$R *.dfm}

constructor TcyEdit.Create(AOwer : TComponent);//TcyEdit类的构造函数
begin
inherited Create(AOwer);
FIsBol := True;//这是对私有成员赋值。对属性IsBol赋值也可
end;

procedure TForm1.Button1Click(Sender: TObject);
var
cyEdit: TcyEdit;
begin
cyEdit := TcyEdit.Create(Self);
cyEdit.Parent := Form1;
// cyEdit.IsBol := true; 在设计时不能进行设置么?
if cyEdit.fIsBol then ShowMessage( 'Yes ') else ShowMessage( 'No ');
if cyEdit.IsBol then ShowMessage( 'Yes ') else ShowMessage( 'No ');
end;

end.