unit1.pas

interface

type MyFile=class
private
	var FFilename:string;
	procedure SetFilename(const S:string);
public
	property Filename:string read FFilename write SetFilename;
end;

implementation
procedure Myfile.SetFilename(const S:string)
begin
	//do something here.
	FFilename=S; // save the new value.
end;