Delphi Modal窗体（ModalResult、ShowModal）的介绍、使用方法和注意事项

//uses  controls
const
  mrNone     = 0;
  mrOk       = idOk;
  mrCancel   = idCancel;
  mrAbort    = idAbort;
  mrRetry    = idRetry;
  mrIgnore   = idIgnore;
  mrYes      = idYes;
  mrNo       = idNo;
  mrAll      = mrNo + 1;
  mrNoToAll  = mrAll + 1;
  mrYesToAll = mrNoToAll + 1;

type
  TModalResult = Low(Integer)..High(Integer);

//uses  windows
const
  IDOK = 1;          ID_OK = IDOK;
  IDCANCEL = 2;      ID_CANCEL = IDCANCEL;
  IDABORT = 3;       ID_ABORT = IDABORT;
  IDRETRY = 4;       ID_RETRY = IDRETRY;
  IDIGNORE = 5;      ID_IGNORE = IDIGNORE;
  IDYES = 6;         ID_YES = IDYES;
  IDNO = 7;          ID_NO = IDNO;
  IDCLOSE = 8;       ID_CLOSE = IDCLOSE;

function ShowModal: Integer; virtual;

function TCustomForm.ShowModal: Integer;
var
  WindowList: Pointer;
  SaveFocusCount: Integer;
  SaveCursor: TCursor;
  SaveCount: Integer;
  ActiveWindow: HWnd;
begin
  CancelDrag;
  if Visible or not Enabled or (fsModal in FFormState) or
    (FormStyle = fsMDIChild) then
    raise EInvalidOperation.Create(SCannotShowModal);
  if GetCapture <> 0 then SendMessage(GetCapture, WM_CANCELMODE, 0, 0);
  ReleaseCapture;
  Application.ModalStarted;
  try
  Include(FFormState, fsModal);
  ActiveWindow := GetActiveWindow;
  SaveFocusCount := FocusCount;
  Screen.FSaveFocusedList.Insert(0, Screen.FFocusedForm);
  Screen.FFocusedForm := Self;
  SaveCursor := Screen.Cursor;
  Screen.Cursor := crDefault;
  SaveCount := Screen.FCursorCount;
  WindowList := DisableTaskWindows(0);
  try
    Show;
    try
      SendMessage(Handle, CM_ACTIVATE, 0, 0);
      ModalResult := 0;
      repeat
        Application.HandleMessage;
        if Application.FTerminate then ModalResult := mrCancel else
          if ModalResult <> 0 then CloseModal;
      until ModalResult <> 0;
      Result := ModalResult;
      SendMessage(Handle, CM_DEACTIVATE, 0, 0);
      if GetActiveWindow <> Handle then ActiveWindow := 0;
    finally
      Hide;
    end;
  finally
    if Screen.FCursorCount = SaveCount then
      Screen.Cursor := SaveCursor
    else Screen.Cursor := crDefault;
    EnableTaskWindows(WindowList);
    if Screen.FSaveFocusedList.Count > 0 then
    begin
      Screen.FFocusedForm := Screen.FSaveFocusedList.First;
      Screen.FSaveFocusedList.Remove(Screen.FFocusedForm);
    end else Screen.FFocusedForm := nil;
    if ActiveWindow <> 0 then SetActiveWindow(ActiveWindow);
    FocusCount := SaveFocusCount;
    Exclude(FFormState, fsModal);
  end;
  finally
    Application.ModalFinished;
  end;
end;

//Form1中:
if Form2.ShowModal = mrok then ShowMessage(‘TaoRoy OK！‘);

//Form2中 
procedure TForm2.button1Click(Sender: TObject);
begin
   self.ModalResult := mrok;
end;