asp.net textbox can only enter numbers, backspace, decimal point (only one decimal point and cannot be in first place)

ASP tutorial. NET textbox can only enter numbers, backspace, decimal point (only one decimal point and cannot be in first place)

private void Textbox1_keypress (object sender, KeyPressEventArgs e)
{
e.handled =! (Char.isnumber (E.keychar) | | | e.keychar = = (char) 8 | | | e.keychar = = '. ');
if (!e.handled) (sender as textbox). Tag = (sender as textbox). text;//Record last correct input
}

private void textBox1_TextChanged (object sender, EventArgs e)
{
if (!system.text.regularexpressions.regex.ismatch (sender as TextBox). Text, @ "^ (?!) 0d) d+ (. d*)? $ ")
{
int index = (sender as textbox). SelectionStart;
(Sender as TextBox). Text = (sender as textbox). Tag as String;
(Sender as TextBox). SelectionStart = index;
}
}

Method Two

if ((E.keychar >= && e.keychar <=) | | e.keychar = + | | e.keychar = 8)
{
No text selected
if (this.textbox1.selectedtext.length = 0)
{
if (E.keychar = 46)
{
Starting position
if (this.textbox1.text.length = 0)
{
E.handled = true;
}
Else
{
if (This.textbox1.text.indexof (".") > 0)
{
E.handled = true;
}
Else
{
e.handled = false;
}
}
}
Else
{
e.handled = false;
}
}
Select text
Else
{
if (E.keychar = 46)
{
String strchar = this.textbox1.text.substring (0, This.textbox1.selectionstart) + this.textbox1.text.substring ( This.textbox1.selectionstart + this.textbox1.selectionlength);
if (Strchar.indexof (".") > 0)
{
E.handled = true;
}
Else
{
e.handled = false;
}
}
}
}
Else
{
E.handled = true;
}