A "dry" principle case

Question

there is a need to check the data entered by the user and display a notification on the screen in case of incorrect input. I used the following method, but it seems to me that it don't quite fit into the principle of "don't repeat yourself". Does anyone have any ideas for simplification?

int productid = 0;
string errorMessage = "Неправильный формат данных:\n",
       productName = "", productGroup = "", productType = "";
if (!int.TryParse(ProductIdTB.Text, out productId))
{
    errorMessage += "+ Номер продукта\n";
}
if (string.IsNullOrEmpty(ProductNameTB.Text))
{
    errorMessage += "+ Название продукта\n";
}
else
{
    productName = ProductNameTB.Text;
}
if (string.IsNullOrEmpty(ProductGroupTB.Text))
{
    errorMessage += "+ Группа продукта\n";
}
else
{
    productGroup = ProductGroupTB.Text;
}
if (string.IsNullOrEmpty(ProductType.Text))
{
    errorMessage += "+ Вид продукта";
}
else
{
    productType = ProductType.Text;
}
if (errorMessage.Split(' ').Length > 1)
{
    MessageBox.Show(errorMessage);
    return;
}

Answer 1

I can imagine building a class that does the checks for you and collects all errors, either in a string or a list of strings.

class ErrorMessageBuilder
{
    string totalmessage = "";

    void AppendErrorIfEmpty(TextBox t, string textboxname)
    {
        if (t.Text.IsNullOrEmpty())
        {
            totalmessage += textboxname + " can't be empty" + Environment.NewLine;
        }    
    }

    void AppendErrorIfNotInt(TextBox t, string textboxname)
    {
         int value;
         if (!int.TryParse(t.Text, out value))
         {
             totalmessage += textboxname + " must be an integer number"  + Environment.NewLine;
         }
    }
}

This would reduce the code to

var emb = ErrorMessageBuilder();
emb.AppendErrorIfNotInt(ProductIdTB, "Product ID");
emb.AppendErrorIfEmpty(ProductNameTB, "Product Name");
...

---

Since this looks like WinForms development to me, you can also have a look at the ErrorProvider class. Like with tooltips, it allows one error message per control. Perhaps that would be even more user-friendly.