对象未创建

Question

I'm creating a non-visual component. Short Code:

// Element of some list item
TMyItem = class
private
  Id: integer;
  Caption: string;
public
  constructor Create(const aId: integer; const aCaption: string);
end;

// List of items
TMyItemList = class(TObjectList<TMyItem>)
public
  constructor Create;
end;

// The component
TMyComp = class(TComponent)
private
  FMyList: TMyItemList;
public
  constructor Create;

implementation

constructor TMyComp.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FMyList:= TMyItemList.Create;
end;

Question: why "FMyList" not exists when "MyComp" created? Assigned(FMyList) = false ...

Answer 1

This is not your actual code. Your actual code compiles. But we can guess what the problem is. Here:

type
  TMyComp = class(TComponent)
  private
    FMyList: TMyItemList;
  public
    constructor Create;
  end;

The constructor for TComponent is declared like this:

constructor Create(AOwner: TComponent); virtual;

It's a virtual constructor because the Delphi streaming framework relies upon metaclasses to create objects. If you want the framework to call your constructor you have to override this virtual constructor.

constructor Create(AOwner: TComponent); override;

I'm reasonably confident of this guess, but we should not need to guess. Next time, please submit real code, a Minimal, Complete, and Verifiable Example .