Delphi Component Creation.. Getting Beyond First Base - delphi

Question

I've used VBto as a starting point plus a lot of study of Delphi 6 User's Guide. I can make my new component compile, but I can't figure a way to get it to display so I can finish debugging it. And 50 years of programming experience isn't helping. Here are the guts of my component:
type
TChangeEvent = procedure(Sender: TObject; v: String) of object;
TTxtSpnr = class(TWinControl)
Lbl: TLabel;
Txt: TEdit;
Scrll: TScrollBar;
private
FonChange: TChangeEvent;
busy, tweaked: Boolean;
NewValue: String;
protected
procedure Changed(v: String); dynamic;
property onChange: TChangeEvent read FonChange write FOnChange;
procedure ScrllChange(Sender: TObject);
procedure ScrllScroll(Sender: TObject; ScrollCode: TScrollCode; var ScrollPos: Integer);
procedure TxtEnter(Sender: TObject);
procedure TxtKeyUp(Sender: TObject; var Key: WORD; Shift: TShiftState);
procedure TxtExit(Sender: TObject);
procedure Txt_Validate(var Cancel: Boolean);
public
function GetCaption(): String;
procedure SetCaption(New_Caption: String);
function GetMax(): Smallint;
procedure SetMax(New_Max: Smallint);
function MaxOf(a: Double; B: Longint): OleVariant;
function MinOf(a: OleVariant; B: Longint): OleVariant;
function GetMin(): Smallint;
procedure SetMin(New_Min: Smallint);
function GetText(): String;
procedure SetText(New_Text: String);
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
published
property Caption: String read GetCaption write SetCaption;
property Enabled: Boolean read GetEnabled write SetEnabled;
property Max: Smallint read GetMax write SetMax;
property Min: Smallint read GetMin write SetMin;
property Text: String read GetText write SetText;
end;
var
TxtSpnr: TTxtSpnr;
implementation
uses Math;
{$R *.dfm}
procedure TTxtSpnr.Changed(V: String); begin
if assigned(FonChange) then FonChange(self,V);
end;
constructor TTxtSpnr.Create(AOwner: TComponent); begin
inherited Create(AOwner);
Lbl := TLabel.Create(Self);
with Lbl do begin
Parent := Self;
end;
Txt := TEdit.Create(Self);
with Txt do begin
Parent := Self;
end;
Scrll := TScrollBar(Self);
with Scrll do begin
Parent := Self;
end;
end;
and here's the test driver:
type
TForm1 = class(TForm)
FTxtSpnr: TTxtSpnr;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject); begin
FTxtSpnr := TTxtSpnr.create(Self);
with FTxtSpnr do begin
Left:=10;
Top:=10;
Visible:=true;
Show;
end;
end;
But it doesn't compile and says, in the constructor, "An object can't be its own parent". Take out the Parent settings, it compiles but doesn't display the components. What am I missing?

Answer 1

First,
Scrll := TScrollBar(Self);
should of course read
Scrll := TScrollBar.Create(Self);
Second,
FTxtSpnr := TTxtSpnr.create(Self);
with FTxtSpnr do begin
Left:=10;
Top:=10;
Visible:=true;
Show;
end;
should be
FTxtSpnr := TTxtSpnr.create(Self);
with FTxtSpnr do
begin
Parent := Self;
Left := 10;
Top := 10;
end;
You forgot to set the parent.
Also, the global variable
var
TxtSpnr: TTxtSpnr;
looks dangerous. If you don't know exactly why you added those two lines, you should probably remove them.