TMemo descendant with empty lines

问题

My TMemo descendant has constructor

constructor TMyMemo.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  Lines.Clear;
end;

When I put TMyMemo on the form I get error "Control '' has no parent window.". Why?

回答1:

A newly created memo has no content. But content is added as soon as the component acquires a name, which is done automatically by the designer. To prevent this, remove csSetCaption from ControlStyle:

constructor TMyMemo.Create(AOwner: TComponent); 
begin 
  inherited Create(AOwner); 
  ControlStyle := ControlStyle - [csSetCaption];
end; 

回答2:

Move Lines.Clear to overriden method CreateWnd. Underlying window control (multiline edit) doesn't exist during Create execution

来源：https://stackoverflow.com/questions/9850176/tmemo-descendant-with-empty-lines