将光标置于错误的文本框上

Question

I have a simple form that takes 9 decimal numbers from 9 textboxes and I put some validation so that the users can only enter decimal numbers and nothing else. Now the challenge I'm having is how to set the cursor in the textbox that had no decimal number after showing the error message in the try-catch statement?

Here's my code:

  private void btn_Aceptar_Click(object sender, EventArgs e)
  {
      POI GPI = new POI();
      POI VIM = new POI();
      POI ST = new POI();

      try
      {
          GPI.POI_x = Convert.ToDecimal(txt_GPIx.Text);
          GPI.POI_y = Convert.ToDecimal(txt_GPIy.Text);
          GPI.POI_z = Convert.ToDecimal(txt_GPIz.Text);
          VIM.POI_x = Convert.ToDecimal(txt_VIMx.Text);
          VIM.POI_y = Convert.ToDecimal(txt_VIMy.Text);
          VIM.POI_z = Convert.ToDecimal(txt_VIMz.Text);
          ST.POI_x = Convert.ToDecimal(txt_STx.Text);
          ST.POI_y = Convert.ToDecimal(txt_STy.Text);
          ST.POI_z = Convert.ToDecimal(txt_STz.Text);
      }
      catch (Exception)
      {
          MessageBox.Show("Ingrese solamente números en las variables GPI/VIM/ST", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
//Set the cursor in the first textbox that had no decimals..
          return;
      }    
      Comisurales Comisurales = new Comisurales();
      Comisurales.calculo_coord_comisurales(PC, AC, IHP, GPI, VIM, ST);                
  }

Let me add that I also have a function to ensure the user is only limited to enter decimals but I wasn't able to figure how to avoid the "." only or this for example: "1."

As an addition to my question, here's what gets validated every time the user press a key in the textbox:

  private void ValidarDecimal(object sender, KeyPressEventArgs e)
  {
      // permitir 0-9, backspace, y decimal
      if (((e.KeyChar < 48 || e.KeyChar > 57) && e.KeyChar != 8 && e.KeyChar != 46))
      {
           e.Handled = true;
            return;
      }

      // chequear solamente un decimal
      if (e.KeyChar == 46)
      {
          if ((sender as TextBox).Text.IndexOf(e.KeyChar) != -1)
               e.Handled = true;
      }
  }

I guess I have 2 ways to resolve my issue. Number one would be find a way to ensure the user never ever enters something weird in the textbox (which I've done partially) and number 2 would be to use the try-catch with the current limitations I mentioned above and then point the user to the textbox that has issues, both are acceptable.

Answer 1

The Decimal class has a TryParse method that could be used to avoid all this logic driven by catching exceptions (a very expensive approach in terms of performance)

decimal value;
if(decimal.TryParse(txt_GPIx.Text, out value))
    GPI.POI_x = value;
else
{
    MessageBox.Show("Invalid decimal value");
    txt_GPIx.Focus();
}

Of course this code needs to be repeated for every control in your list, but you could write a generic function like this one

private decimal GetValueAndValidate(Textbox txt, out bool isOK)
{
    isOK = true;
    decimal value = 0m;
    if(!decimal.TryParse(txt.Text, out value))
    {
        MessageBox.Show("Invalid decimal value");
        txt.Focus();
        isOK = false;
    }
    return value;
}

and then use the following approach in your code inside the button click

 bool isOK = true;
 if(isOK) GPI.POI_x = GetValueAndValidate(txt_GPIx, out isOK);
 if(isOK) GPI.POI_y = GetValueAndValidate(txt_GPIy, out isOK);
 .... and so on for the other fields ....

For the second part of your question, finding a way to completely control the input logic is not easy. What happens for example if your user PASTE an invalid text in your textbox? There are very edge case situations that takes a lot of effort to code correctly. It is a lot more easy to leave freedom of typing to your user and apply a strict logic when you get that input.