Delphi component to show some text file at design time

uDesignNote.pas

unit uDesignNote;

interface

uses
  System.SysUtils, System.Classes, Vcl.Forms, Vcl.StdCtrls;

type
  TDesignNote = class(TComponent)
  private
    FContentForm: TForm;
    FFileName: string;
    function GetContentForm: TForm;
    function GetMemo: TMemo;
    function GetVisible: Boolean;
    procedure HideFileContent;
    procedure SetFileName(const Value: string);
    procedure SetVisible(const Value: Boolean);
    procedure ShowFileContent;
    procedure UpdateView;
  protected
    procedure Notification(AComponent: TComponent; Operation: TOperation);
      override;
  public
    destructor Destroy; override;
    property ContentForm: TForm read GetContentForm;
    property Memo: TMemo read GetMemo;
  published
    property FileName: string read FFileName write SetFileName;
    property Visible: Boolean read GetVisible write SetVisible;
  end;

procedure Register;

implementation

uses
  Vcl.Controls, System.IOUtils;

procedure Register;
begin
  RegisterComponents('Samples', [TDesignNote]);
end;

destructor TDesignNote.Destroy;
begin
  Visible := False;
  inherited;
end;

function TDesignNote.GetContentForm: TForm;
var
  memo: TMemo;
begin
  if FContentForm = nil then begin
    FContentForm := TForm.Create(Application);
    memo := TMemo.Create(FContentForm);
    memo.Parent := FContentForm;
    memo.Align := alClient;
  end;
  result := FContentForm;
end;

function TDesignNote.GetMemo: TMemo;
begin
  Result := (ContentForm.Controls[0] as TMemo);
end;

function TDesignNote.GetVisible: Boolean;
begin
  Result := (FContentForm <> nil) and FContentForm.Visible;
end;

procedure TDesignNote.HideFileContent;
begin
  if FContentForm <> nil then begin
    FContentForm.Free;
    FContentForm := nil;
  end;
end;

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

procedure TDesignNote.SetFileName(const Value: string);
begin
  if FFileName <> Value then
  begin
    FFileName := Value;
    UpdateView;
  end;
end;

procedure TDesignNote.SetVisible(const Value: Boolean);
begin
  if Value or (FContentForm <> nil) then begin
    ContentForm.Visible := Value;
  end;
end;

procedure TDesignNote.ShowFileContent;
begin
  ContentForm.Show;
  if TFile.Exists(FileName) then begin
    Memo.Lines.LoadFromFile(FileName);
  end
  else begin
    Memo.Lines.Clear;
  end;
end;

procedure TDesignNote.UpdateView;
begin
  if csDesigning in ComponentState then begin
    ShowFileContent;
  end;
end;

end.