代码片断

procedure TMainForm.ActionNewExecute(Sender: TObject);

var
 
 OldChildForm, NewChildForm: TChildForm;  // TChildForm是自建的子窗体类

begin
  OldChildForm := TChildForm(ActiveMDIChild);  // 取得当前活动子窗口
 
Inc (Counter);
 
NewChildForm := TChildForm.Create (Self);
 
 NewChildForm.Caption :=
  
 LowerCase (ExtractFilePath (Application.Exename)) +
 
   'text' + IntToStr (Counter) + '.txt';
 
 if Assigned(OldChildForm) then OldChildForm.Show  // 重新显示旧的窗口
 
else NewChildForm.Show;

end;