如何在 DFM 中防止不需要的 object

Question

I copied the source LabeledEdit example with a TBoundLabel in components I'm writing to attach a convenient label to. They work fine but I'm getting issues loading the.dfm form (seemingly when my component is on another such as a CategoryPanel):

Class TBoundLabel not found

Test form:

object Form2: TForm2
  Left = 0
  Top = 0
  Caption = 'Form2'
  ClientHeight = 518
  ClientWidth = 635
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object CategoryPanelGroup1: TCategoryPanelGroup
    Left = 0
    Top = 70
    Width = 635
    Height = 448
    VertScrollBar.Tracking = True
    Align = alClient
    HeaderFont.Charset = DEFAULT_CHARSET
    HeaderFont.Color = clWindowText
    HeaderFont.Height = -11
    HeaderFont.Name = 'Tahoma'
    HeaderFont.Style = []
    TabOrder = 0
    object CategoryPanel1: TCategoryPanel
      Top = 0
      Caption = 'CategoryPanel1'
      TabOrder = 0
    end
    object CategoryPanel2: TCategoryPanel
      Top = 200
      Caption = 'CategoryPanel2'
      TabOrder = 1
      object SubLabel: TBoundLabel
        Width = 78
        Height = 13
        Caption = 'LabelledCombo1'
      end
      object LabelledCombo1: TLabelledCombo
        Left = 152
        Top = 80
        Width = 145
        Height = 21
        LabelRotulo.Width = 78
        LabelRotulo.Height = 13
        LabelRotulo.Caption = 'LabelledCombo1'
        TabOrder = 0
      end
    end
  end
  object Panel1: TPanel
    Left = 0
    Top = 0
    Width = 635
    Height = 41
    Align = alTop
    Caption = 'Panel1'
    TabOrder = 1
  end
  object ToolBar1: TToolBar
    Left = 0
    Top = 41
    Width = 635
    Height = 29
    Caption = 'ToolBar1'
    TabOrder = 2
  end
end

Source for the LabelledCombo:

unit LabelledComboU;

interface

uses
  WinApi.Windows,
  WinApi.Messages,
  System.SysUtils,
  System.Math,
  System.UITypes,
  System.StrUtils,
  System.Classes,
  System.Types,
  VCL.Forms,
  VCL.ExtCtrls,
  VCL.Controls,
  VCL.Consts,
  VCL.Dialogs,
  VCL.ImgList,
  VCL.Samples.Spin,
  VCL.StdCtrls,
  VCL.GraphUtil,
  VCL.Graphics,
  VCL.THemes,
  VCL.Styles;

type
  TLabelledCombo = class(TCustomComboBox)
  private
    FLabel: TBoundLabel;
    FLabelPosition: TLabelPosition;
    FLabelSpacing: Integer;
    procedure SetLabelPosition(const Value: TLabelPosition);
    procedure SetLabelSpacing(const Value: integer);
  protected
    procedure SetParent(AParent: TWinControl); override;
    procedure Notification(AComponent: TComponent; Operation: TOperation); override;
    procedure SetName(const Value: TComponentName); override;
    procedure CMVisiblechanged(var Message: TMessage);
      message CM_VISIBLECHANGED;
    procedure CMEnabledchanged(var Message: TMessage);
      message CM_ENABLEDCHANGED;
    procedure CMBidimodechanged(var Message: TMessage);
      message CM_BIDIMODECHANGED;
  public
    constructor Create(AOwner: TComponent); override;
    procedure SetBounds(ALeft: Integer; ATop: Integer; AWidth: Integer; AHeight: Integer); override;
    procedure SetupInternalLabel;
  published
    property LabelRotulo: TBoundLabel read FLabel;
    property LabelPosition: TLabelPosition read FLabelPosition write SetLabelPosition default lpAbove;
    property LabelSpacing: Integer read FLabelSpacing write SetLabelSpacing default 3;
    property Align;
    property AutoComplete default True;
    property AutoCompleteDelay default 500;
    property AutoDropDown default False;
    property AutoCloseUp default False;
    property BevelEdges;
    property BevelInner;
    property BevelKind default bkNone;
    property BevelOuter;
    property Style; { Must be published before Items }
    property Anchors;
    property BiDiMode;
    property CharCase;
    property Color;
    property Constraints;
    property Ctl3D;
    property DoubleBuffered;
    property DragCursor;
    property DragKind;
    property DragMode;
    property DropDownCount;
    property Enabled;
    property ExtendedUI default False;
    property Font;
    property ImeMode;
    property ImeName;
    property ItemHeight;
    property ItemIndex default -1;
    property MaxLength;
    property ParentBiDiMode;
    property ParentColor;
    property ParentCtl3D;
    property ParentDoubleBuffered;
    property ParentFont;
    property ParentShowHint;
    property PopupMenu;
    property ShowHint;
    property Sorted;
    property TabOrder;
    property TabStop;
    property Text;
    property TextHint;
    property Touch;
    property Visible;
    property StyleElements;
    property StyleName;
    property OnChange;
    property OnClick;
    property OnCloseUp;
    property OnContextPopup;
    property OnDblClick;
    property OnDragDrop;
    property OnDragOver;
    property OnDrawItem;
    property OnDropDown;
    property OnEndDock;
    property OnEndDrag;
    property OnEnter;
    property OnExit;
    property OnGesture;
    property OnKeyDown;
    property OnKeyPress;
    property OnKeyUp;
    property OnMeasureItem;
    property OnMouseEnter;
    property OnMouseLeave;
    property OnSelect;
    property OnStartDock;
    property OnStartDrag;
    property Items; { Must be published after OnMeasureItem }
  end;

implementation

{ TLabelledCombo }

procedure TLabelledCombo.CMBidimodechanged(var Message: TMessage);
begin
  if FLabel <> nil then
    FLabel.BiDiMode := BiDiMode;
end;

procedure TLabelledCombo.CMEnabledchanged(var Message: TMessage);
begin
  inherited;
  if FLabel <> nil then
    FLabel.Enabled := Enabled;
end;

procedure TLabelledCombo.CMVisiblechanged(var Message: TMessage);
begin
  inherited;
  if FLabel <> nil then
    FLabel.Visible := Visible;
end;

constructor TLabelledCombo.Create(AOwner: TComponent);
begin
  inherited;
  FLabelPosition := lpAbove;
  FLabelSpacing := 3;
  SetupInternalLabel;
end;

procedure TLabelledCombo.Notification(AComponent: TComponent;
  Operation: TOperation);
begin
  inherited Notification(AComponent, Operation);
  if (AComponent = FLabel) and (Operation = opRemove) then
    FLabel := nil;
end;

procedure TLabelledCombo.SetBounds(ALeft, ATop, AWidth, AHeight: Integer);
begin
  inherited SetBounds(ALeft, ATop, AWidth, AHeight);
  SetLabelPosition(FLabelPosition);
end;

procedure TLabelledCombo.SetLabelPosition(const Value: TLabelPosition);
var
  P: TPoint;
begin
  if FLabel = nil then Exit;
  FLabelPosition := Value;
  case Value of
    lpAbove:
      P := Point(Left, Top - FLabel.Height - FLabelSpacing);
    lpBelow:
      P := Point(Left, Top + Height + FLabelSpacing);
    lpLeft : P := Point(Left - FLabel.Width - FLabelSpacing,
                    Top + ((Height - FLabel.Height) div 2));
    lpRight: P := Point(Left + Width + FLabelSpacing,
                    Top + ((Height - FLabel.Height) div 2));
  end;
  FLabel.SetBounds(P.x, P.y, FLabel.Width, FLabel.Height);
end;

procedure TLabelledCombo.SetLabelSpacing(const Value: integer);
begin
  FLabelSpacing := Value;
  SetLabelPosition(FLabelPosition);
end;

procedure TLabelledCombo.SetName(const Value: TComponentName);
var
  LClearText: Boolean;
begin
  if (csDesigning in ComponentState) and (FLabel <> nil) and
     ((Flabel.GetTextLen = 0) or
     (CompareText(FLabel.Caption, Name) = 0)) then
    FLabel.Caption := Value;
  LClearText := (csDesigning in ComponentState) and (Text = '');
  inherited SetName(Value);
  if LClearText then
    Text := '';
end;

procedure TLabelledCombo.SetParent(AParent: TWinControl);
begin
  inherited SetParent(AParent);
  if FLabel = nil then exit;
  FLabel.Parent := AParent;
  FLabel.Visible := True;
end;

procedure TLabelledCombo.SetupInternalLabel;
begin
  if Assigned(FLabel) then exit;
  FLabel := TBoundLabel.Create(Self);
  FLabel.FreeNotification(Self);
//  FLabel.FocusControl := Self;
end;

end.

This is the barest test which reproduces the problem, a LabelledCombo on a CategoryPanel. (On a form I am not getting grief.)

I tried deleting the reference to Sublabel and resaving the.DFM but it comes back again. I can't see what to fix: the source is identical to that of TLabeledEdit except that TBoundLabel is not in my Unit. Do I need to copy the source of that too into my component unit?

Mike

Answer 1

The problem is that you are trying to re-use TBoundLabel - which has been designed specifically to be used from within TCustomLabeledEdit only. Using it elsewhere will lead to unwanted side effects. In the code below (taken from VCL.ExtCtrls.pas) you can easily see that TBoundLabel is basically bound to TCustomLabeledEdit.

If that is a smart design, is a different question though.

procedure TBoundLabel.AdjustBounds;
begin
  inherited AdjustBounds;
  if Owner is TCustomLabeledEdit then
    with Owner as TCustomLabeledEdit do
      SetLabelPosition(LabelPosition);
end;

Answer 2

There is a bug in Delphi Sydney, whereby a TLabeledEdit placed on a TCategoryPanel gives the fault I raised in my query.

How to experience it

1. Place a TCategoryPanelGroup on a form, create a couple of TCategoryPanels on it
2. Place an ordinary Panel on the form.
3. Place a TLabeledEdit on step 2's Panel.
4. View as Text then View as Form (Alt/F12) there should be no problem.
5. Move the TLabeledEdit off the Panel and onto one of the TCategoryPanels.
6. Repeat step 4.

Try moving it onto another TPanel on one of the TCategoryPanels: again there is no problem.

No wonder I had trouble with my labelled components....