Can't use Decimal values - windows-phone-7

Question

I've created a TextBox in which currency values have to be entered but now I am not able to enter .(dot) in the textbox for decimal values. I have written the code in Text_changed event.
The code
int cursorLocation = ((TextBox)(sender)).SelectionStart;
string inputval = ((TextBox)sender).Text;
inputval = inputval.Replace("*", "");
inputval = inputval.Replace("#", "");
inputval = inputval.Replace(",", "");
inputval = inputval.Replace(" ", "");
inputval = inputval.Replace("-", "");
Decimal inputval1 = Convert.ToDecimal(inputval);
((TextBox)sender).Text = inputval1.ToString("###,###");
cursorLocation = ((TextBox)(sender)).Text.Length;
//((TextBox)sender).Text = inputval;
((TextBox)(sender)).SelectionStart = cursorLocation;

Answer 1

This is the problem
((TextBox)sender).Text = inputval1.ToString("###,###");
Whenever you enter new character, the whole textbox.text gets overwritten with the new text in the format ###,###

Answer 2

I just did this under textchanged event and this worked,
try
{
string value = TextBox.Text.Replace(",", "");
long ul;
if (long.TryParse(value, out ul))
{
TextBox.TextChanged -= TextBox_TextChanged;
TextBox.Text = string.Format("{0:#,#}", ul);
TextBox.SelectionStart = TextBox.Text.Length;
TextBox.TextChanged += TextBox_TextChanged;
this.TextBox.MaxLength = 10;
}
}
catch { }