Mega Code Archive
Creating class properties
<![CDATA[
Title: Creating class properties
Question: This article demonstrates how to add a class property to a new component like the Font property on most components.
Answer:
The following example declares a class, TMyClassProp which contains several fields including an enumerated type field.
Notes:
1. PropertyObject - must be of type TPersistant or a descendant
class of TPersistant.
2. Must create an instance of this TMyClassProp in the Create
of the component.
unit SubClass;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls,
Forms, Dialogs;
type
{ First Create a enumerated list of elements
then create a set of these elements }
TEnumList = (Mom, Dad, Sibling, Sister, Brother);
TEnum = set of TEnumList;
{ Here is the Class Object we want to use as a property in
our Component.
It has 4 properties, a Boolean, Word, String, and the
enumerated type. }
TMyClassProp = class(TPersistent)
FBool: Boolean;
FWord: Word;
FString: String;
FEnum: TEnum;
published
property HaveCar: Boolean read FBool Write FBool;
property Age: Word read FWord write FWord;
property Name: String read FString write FString;
property Relation: TEnum read FEnum write FEnum;
end; // TMyClassProp
{ Now create the component which will contain a property of
type TMyClassProp.}
TMyComponent = class(TComponent)
FEnum: TEnum; { Enumerated type, just for fun }
FSubClass: TMyClassProp; { The Class Property we want }
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
published
property Relation: TEnum read FEnum write FEnum;
property Relative: TMyClassProp read FSubClass write FSubClass;
{ Published declarations }
end;
procedure Register;
implementation
{ Override Create, to create an instance of the Class property.
This is required. }
constructor TMyComponent.Create(AOwner: TComponent);
begin
inherited;
FSubClass := TMyClassProp.Create;
end;
{ Override Destroy to perform house cleaning. }
destructor TMyComponent.Destroy;
begin
FSubClass.Free;
inherited;
end;
procedure Register;
begin
RegisterComponents('Samples', [TMyComponent]);
end;
end.
]]>