public void AddUser(UserInfo user)
 {
     if (Model.Exists(user.Phone))
     {
         View.AppendNotifierText("This user already exists");
     }
     else
     {
         Model.Add(user);
         View.AppendNotifierText("New user was added");
     }
 }
 public void EditUser(UserInfo editedUser)
 {
     if (Model.Exists(editedUser.Name, editedUser.Surname, editedUser.Phone))
     {
         View.AppendNotifierText("Not unique attributes");
     }
     else
     {
         View.AppendNotifierText("User was edited.");
         Model.Edit(editedUser);
         View.DisableEdittingUsers();
     }
 }
 public void DeleteUser(UserInfo userInfo)
 {
     try
     {
         if (Model.Exists(userInfo.Name, userInfo.Surname))
         {
             Model.Delete(userInfo.Name, userInfo.Surname);
             View.AppendNotifierText("User was deleted.");
             View.DisableEdittingUsers();
         }
         else
         {
             View.AppendNotifierText("This user doesn't exist.");
         }
     }
     catch (ArgumentNullException)
     {
         View.ShowMessageBox("User is null");
     }
 }