Validation-Textboxes allowing only decimals

Question

I am using following code for validating textbox.

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    e.Handled = SingleDecimal(sender, e.KeyChar);
}

public bool SingleDecimal(System.Object sender, char eChar)
{
    string chkstr = "0123456789.";
    if (chkstr.IndexOf(eChar) > -1 || eChar == Constants.vbBack) 
    {
        if (eChar == ".") 
        {
            if (((TextBox)sender).Text.IndexOf(eChar) > -1) 
            {     
                return true;
            }
            else 
            {         
                return false;  
            }
        }   
        return false;
     }
     else 
     {
         return true;  
     }
}

Problem is Constants.vbBack is showing error.If i didnt use Constants.vbBack,backspace is not workimg.What alteration can i make to work backspace.Can anybody help?

Answer 1

here is the code I would use...

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    // allows 0-9, backspace, and decimal
    if (((e.KeyChar < 48 || e.KeyChar > 57) && e.KeyChar != 8 && e.KeyChar != 46))
    {
        e.Handled = true;
        return;
    }

    // checks to make sure only 1 decimal is allowed
    if (e.KeyChar == 46)
    {
        if ((sender as TextBox).Text.IndexOf(e.KeyChar) != -1)
            e.Handled = true;
    }
}

Answer 2

You can make a method to check if it's a number.

Instead of checking for the . as a decimal separator you should get it from CurrentCulture object as it could be another character depending on where in the world you are.

public bool isNumber(char ch, string text)
{
    bool res = true;
    char decimalChar = Convert.ToChar(CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator);

    //check if it´s a decimal separator and if doesn´t already have one in the text string
    if (ch == decimalChar && text.IndexOf(decimalChar) != -1)
    {
        res = false;
        return res;
    }

    //check if it´s a digit, decimal separator and backspace
    if (!Char.IsDigit(ch) && ch != decimalChar && ch != (char)Keys.Back)
        res = false;

    return res;
}

Then you can call the method in the KeyPress event of the TextBox:

private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if(!isNumber(e.KeyChar,TextBox1.Text))
        e.Handled=true;
}