How to add a TListBox to a form at runtime?

[TheDuke]

Hello, consider this code:
procedure TForm1.Button1Click(Sender: TObject);
var FRec:TSearchrec;
ListBox1:TListBox;
begin
listbox1:=Tlistbox.Create(Self);
listbox1.Visible:=false;
listbox1.Sorted:=True;
ris:=findfirst('c:\*.*',faAnyFile,FRec);
while ris=0 do begin
listbox1.Items.Add(frec.name);
ris:=findnext(FRec);
end;
findclose(Frec);
listbox1.destroy;
end;

When i execute it, i get an EInvalidOperation exception with message "Control has no parent window".
What is wrong? i tried using FORM1 instead of the Self pointer, but still got the same error.

[pascal.enz]

To create a control at runtime, you must set the parent property of the control. So you have to add the command listbox1.parent := self;

P.S. You should never destroy a component with the "destroy" command. Use "free" instead! And to be sure that all allocated memory is released after an possible excepten, you should use a try...finally structure.

The correct code should look like this.

procedure TForm1.Button1Click(Sender: TObject);
var FRec:TSearchrec;
ListBox1:TListBox;
begin
listbox1:=Tlistbox.Create(Self);
try
listbox1.Visible:=false;
listbox1.Sorted:=True;
listbox1.Parent := Self;
ris:=findfirst('c:\*.*',faAnyFile,FRec);
while ris=0 do begin
listbox1.Items.Add(frec.name);
ris:=findnext(FRec);
end;
findclose(Frec);
finally
listbox1.free;
end;
end;

[Lapince]

Just add "listbox1.parent:=form1" after "create"...