Windows Forms C# - Dynamic mask textbox money Input

Question

Windows Forms C# - I would like to make a textbox that automatically changes each time a user types or deletes one key from the textbox. I developed part of code.

    //This will convert value from textbox to currency format when focus leave textbox
    private void txtValormetrocubico_Leave(object sender, EventArgs e)
    {
        decimal cubic = Convert.ToDecimal(txtValormetrocubico.Text);
        txtValormetrocubico.Text = string.Format("{0:c}", Convert.ToDecimal(cubic));
        MessageBox.Show(txtValormetrocubico.Text);
    }


    //this only allow numbers and "." and "," on textimbox imput
    private void txtValormetrocubico_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!char.IsControl(e.KeyChar)
    && !char.IsDigit(e.KeyChar)
    && e.KeyChar != '.' && e.KeyChar != ',')
        {
            e.Handled = true;
        }

        // only allow one decimal point
        if (e.KeyChar == '.'
            && (sender as TextBox).Text.IndexOf('.') > -1)
        {
            e.Handled = true;
        }

            if (e.KeyChar == ','
                && (sender as TextBox).Text.IndexOf(',') > -1)
            {
                e.Handled = true;
            }          
    }

The first time I enter a value in the text box, the value is converted to currency format perfectly, like 300 to $ 300.00 . But I edit this textbox value again and press enter, it gives an error: "Input String was not in a Correct Format" pointing to the line below:

decimal cubic = Convert.ToDecimal(txtValormetrocubico.Text);

I think the problem is caused by the fact that the value is already in decimal format. So when I click on the field and press enter again, it causes an error because the value cannot be parsed. How do I avoid this error ?

EDIT: My previous question was my first. As I am new user and don't have much knowledge in C#, I forgot to post my code. After studying some more, I made part of it work. Only this little problem remains. Please vote up, I was banned and cant make new questions because I had 7 down votes.

Thanks guys.

Answer 1

The problem is that the string contains the currency symbol

private void TextBox_LeaveEvent(object sender, EventArgs e)
{
    var tb = sender as TextBox;
    if(tb.Text.Length>0){
        decimal cubic = Convert.ToDecimal(tb.Text);
        tb.Text = string.Format("{0:c}", Convert.ToDecimal(cubic));
        label1.Text = tb.Text;
    }
}

Above the textbox.Text is set to contain the currency information:

tb.Text = string.Format("{0:c}", Convert.ToDecimal(cubic));

Since the textbox now contains a currency symbol (like € or $) the Convert.ToDecimal fails as soon as the TextBox_LeaveEvent fires again:

decimal cubic = Convert.ToDecimal(tb.Text);

If you bing for c# masked textbox you can find articles about masked textboxes. You cold also test if the string contains any non-number-charakters ( if(tbText.IndexOf(" ") >-1){...} )

Update with basic example

I uploaded a very basic example to remove the currency formating to github:

string RemoveCurrencyFormating(string input)
{    
    if(input.IndexOf(" ") !=-1){
       var money = input.Substring(0, input.IndexOf(" ")-1);            
       return String.Format("{0:D0}", money);               
    }
    return ""; // Todo: add Error Handling
}

On TextBox Enter Event you can do the following:

void TextBox_EnterEvent(object sender, EventArgs e)
{
    var tb = sender as TextBox;
    tb.Text = RemoveCurrencyFormating(tb.Text);
}