“控件''没有父窗口”错误

Question

当我将控件放在表单上时出现此错误。 错误出现在这里：

  TAssociateFileExt = class(TGroupBox)
  private
  protected
  public
    btnAssociate   : TButton;
    constructor Create(aOwner: TComponent); override;
  end;

constructor TAssociateFileExt.Create(aOwner: TComponent);
begin
 inherited Create(aOwner);
 Caption:= '';                       <-------- error here
 ClientHeight:= 125;                 <-------- and here
 ClientWidth := 170;
 DoubleBuffered:= TRUE;

 btnAssociate:= TButton.Create(Self);
 btnAssociate.Parent:= Self;
 btnAssociate.Visible:= TRUE;
 btnAssociate.Left:= 17;
 btnAssociate.Top:= 26;
 btnAssociate.Width:= 142;
 btnAssociate.Height:= 25;
 btnAssociate.Hint:= 'Associate this application with its files. When you double click a file this program will automatically start and load that file.';
 btnAssociate.Caption:= 'Associate';
 btnAssociate.DoubleBuffered:= TRUE;
 btnAssociate.ParentDoubleBuffered:= FALSE;
 btnAssociate.TabOrder:= 0;
 btnAssociate.OnClick:= btnAssociateClick;

 btnAssociateDel:= TButton.Create(Self);
 btnAssociateDel.Parent:= Self;
 btnAssociateDel.Visible:= TRUE;
 btnAssociateDel.Left:= 17;
 btnAssociateDel.Top:= 53;
 btnAssociateDel.Width:= 142;
 btnAssociateDel.Height:= 25;
 btnAssociateDel.Hint:= 'Remove association';
 btnAssociateDel.Caption:= 'Remove association';
 btnAssociateDel.DoubleBuffered:= TRUE;
 btnAssociateDel.ParentDoubleBuffered:= FALSE;
 btnAssociateDel.TabOrder:= 1;
 btnAssociateDel.OnClick:= btnAssociateDelClick;

 chkAllUsers:= TCheckBox.Create(Self);
 chkAllUsers.Parent:= Self;
 chkAllUsers.Visible:= TRUE;
 chkAllUsers.Left:= 31;
 chkAllUsers.Top:= 97;
 chkAllUsers.Width:= 115;
 chkAllUsers.Height:= 17;
 chkAllUsers.Hint:= 'Please note that if you want to do this for all users then you need administrator/elevated rights.';
 chkAllUsers.Caption:= 'Do this for all users';
 chkAllUsers.DoubleBuffered:= TRUE;
 chkAllUsers.ParentDoubleBuffered:= FALSE;
 chkAllUsers.TabOrder:= 2;
 chkAllUsers.OnClick:= chkAllUsersClick;
end;

答案可能是“标题需要一个有效的窗口句柄”。正确的？但是，David Intersimone (here) 的一篇文章说可以在构造函数中设置 Caption。

1. 文章有误吗？
2. 我应该在 CreateWnd 中移动代码（Caption 和 TButton.Create）吗（因为 AfterConstruction 不是一个好地方）？问题是 CreateWnd 可以被多次调用：“CreateWnd 在首次创建控件或必须销毁并重新创建底层屏幕对象以反映属性更改时自动调用。”

---

更新：
在将 (aOwner: TComponent) 添加到构造函数的声明（在实现中）后，按照 J... 的建议，错误移至下一行 (clientheight:= 90);

Answer 1

我在 CreateWindowHandle 中移动了代码。现在它起作用了。 完整代码：

UNIT cAssociateExt;

INTERFACE

USES
  Windows, Messages, SysUtils, Classes, Controls, ExtCtrls, Forms, StdCtrls;

TYPE
  TAssociateFileExt = class(TGroupBox)
  private
  protected
  public
    btnAssociate   : TButton;
    btnAssociateDel: TButton;
    chkAllUsers    : TCheckBox;
    constructor Create(aOwner: TComponent); override;
    procedure AfterConstruction;  override;
    procedure CreateWindowHandle(const Params: TCreateParams); override;
    ...
  published
  end;


procedure Register;


IMPLEMENTATION


procedure TAssociateFileExt.AfterConstruction;
begin
 inherited;         //Not a good place here
end;


procedure TAssociateFileExt.CreateWindowHandle(const Params: TCreateParams);
begin
 inherited;

 //DO NOT CREATE CONTROLS HERE! See: Sertac Akyuz's comment

 Caption:= '';    
 ClientHeight:= 125;
 ClientWidth := 170;
end;



constructor TAssociateFileExt.Create(aOwner: TComponent);
begin
 inherited Create(aOwner);
 DoubleBuffered:= TRUE;

 btnAssociate:= TButton.Create(Self);
 btnAssociate.Parent:= Self;
 btnAssociate.Visible:= TRUE;
 btnAssociate.Left:= 17;
 ...
end;

Answer 2

重要提示： 当您创建组件时，您需要在构造函数过程中使用此行以避免“控件没有父窗口”。

继承的创建（AOwner）； 父级：=TWinControl(AOwner);