delphi – TEdit和WM_PAINT消息处理程序的奇怪行为

type
  TEdit = class(StdCtrls.TEdit)
  private
    FEllipsis: Boolean;
    FCanvas: TCanvas;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;

constructor TEdit.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FEllipsis := False;
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;

destructor TEdit.Destroy;
begin
  FCanvas.Free;
  inherited;
end;

procedure TEdit.WMPaint(var Message: TWMPaint);
begin
  if FEllipsis and (not Focused) then
  begin
    // Message.Result := 0;
    // TODO...
  end
  else
    inherited;
end;

请注意,当FEllipsis和(未聚焦)消息处理程序不执行任何操作时.

现在我在表单上删除了TButton和2个TEdit控件,并添加了OnCreate形式：

procedure TForm1.FormCreate(Sender: TObject);
begin
  Edit2.FEllipsis := True;
end;

我希望Edit1正常绘制,Edit2不要在编辑控件中绘制任何内容.

相反,消息处理程序被无休止地处理,Edit1也没有被绘制,整个应用程序都在窒息(占用率为25％！).我也尝试过返回Message.Result：= 0 – 效果相同.

现在,对于“奇怪”部分：当我使用BeginPaint获取画布句柄时,一切都按预期工作.

procedure TEdit.WMPaint(var Message: TWMPaint);
var
  PS: TPaintStruct;
begin
  if FEllipsis and (not Focused) then
  begin    
    if Message.DC = 0 then
      FCanvas.Handle := BeginPaint(Handle,PS)
    else
      FCanvas.Handle := Message.DC;
    try
      // paint on FCanvas...
    finally
      FCanvas.Handle := 0;
      if Message.DC = 0 then EndPaint(Handle,PS);
    end;
  end
  else
    inherited;
end;

注意我也没有调用继承.

如何解释这种行为？谢谢.