You can done this in following ways:
1.AjaxFilteredTextBoxExtender
here you first add reference of ajax toolkit and this extender.
you can set ValidChars to "." for decimal which allo user to enter numeric value with decimal point.
<ajaxToolkit:FilteredTextBoxExtender ID="ftbe" runat="server"
TargetControlID="TextBox3"
FilterType="Custom, Numbers"
ValidChars="." />
2.using javscript
<script type="text/javascript">
// price text-box allow numeric and allow 2 decimal points only
function extractNumber(obj, decimalPlaces, allowNegative)
{
var temp = obj.value;
// avoid changing things if already formatted correctly
var reg0Str = '[0-9]*';
if (decimalPlaces > 0) {
reg0Str += '\\.?[0-9]{0,' + decimalPlaces + '}';
} else if (decimalPlaces < 0) {
reg0Str += '\\.?[0-9]*';
}
reg0Str = allowNegative ? '^-?' + reg0Str : '^' + reg0Str;
reg0Str = reg0Str + '$';
var reg0 = new RegExp(reg0Str);
if (reg0.test(temp)) return true;
// first replace all non numbers
var reg1Str = '[^0-9' + (decimalPlaces != 0 ? '.' : '') + (allowNegative ? '-' : '') + ']';
var reg1 = new RegExp(reg1Str, 'g');
temp = temp.replace(reg1, '');
if (allowNegative) {
// replace extra negative
var hasNegative = temp.length > 0 && temp.charAt(0) == '-';
var reg2 = /-/g;
temp = temp.replace(reg2, '');
if (hasNegative) temp = '-' + temp;
}
if (decimalPlaces != 0) {
var reg3 = /\./g;
var reg3Array = reg3.exec(temp);
if (reg3Array != null) {
// keep only first occurrence of .
// and the number of places specified by decimalPlaces or the entire string if decimalPlaces < 0
var reg3Right = temp.substring(reg3Array.index + reg3Array[0].length);
reg3Right = reg3Right.replace(reg3, '');
reg3Right = decimalPlaces > 0 ? reg3Right.substring(0, decimalPlaces) : reg3Right;
temp = temp.substring(0,reg3Array.index) + '.' + reg3Right;
}
}
obj.value = temp;
}
function blockNonNumbers(obj, e, allowDecimal, allowNegative)
{
var key;
var isCtrl = false;
var keychar;
var reg;
if(window.event) {
key = e.keyCode;
isCtrl = window.event.ctrlKey
}
else if(e.which) {
key = e.which;
isCtrl = e.ctrlKey;
}
if (isNaN(key)) return true;
keychar = String.fromCharCode(key);
// check for backspace or delete, or if Ctrl was pressed
if (key == 8 || isCtrl)
{
return true;
}
reg = /\d/;
var isFirstN = allowNegative ? keychar == '-' && obj.value.indexOf('-') == -1 : false;
var isFirstD = allowDecimal ? keychar == '.' && obj.value.indexOf('.') == -1 : false;
return isFirstN || isFirstD || reg.test(keychar);
}
// end of price text-box allow numeric and allow 2 decimal points only
</script>
<input type="text" name="price" value="" size="10" onblur="extractNumber(this,2,false);" onkeyup="extractNumber(this,2,false);" onkeypress="return blockNonNumbers(this, event, true, false);" />