Title: How to override a property
Question: Trigger-methods of properties are sometimes declared in the private-section of a class... there is a simply trick how to override these properties.
Answer:
An example to show this is the TEdit class. Lets say we want to make the background-color of this control gray when ReadOnly is set to true.
The problem is that SetReadOnly is private.. so can not be overriden. The solution is to simply REPLACE the SetReadOnly function and call inherited with the ReadOnly-property of the parent-class:
inherited ReadOnly:= Value;
All other code (Loaded, Create) is just to get the correct default-color that was set by the developer at design-time.
type
TMyEdit = class(TEdit)
private
FDesignColor: TColor;
FReadOnly: boolean;
procedure SetReadOnly(Value: boolean);
procedure SetColor;
protected
procedure Loaded; override;
public
constructor Create(AOwner: TComponent); override;
published
property ReadOnly: boolean read FReadOnly write SetReadOnly;
end;
implementation
constructor TMyEdit.Create(AOwner: TComponent);
begin
inherited;
FDesignColor:= clWindow;
end;
procedure TMyEdit.Loaded;
begin
inherited;
FDesignColor:= Color;
end;
procedure TMyEdit.SetColor;
begin
if ReadOnly then
Color:= clBtnFace
else
Color:= FDesignColor;
end;
procedure TMyEdit.SetReadOnly(Value: boolean);
begin
FReadOnly:= Value;
inherited ReadOnly:= Value;
SetColor;
end;