为了实现验证，.net提供了一个javascript脚本，当我们生成一个asp.net页面时，通过查看页面源代码的方式，会发现都调用了下面一个javascript文件：
<script src="WebResource.axd" type="text/javascript"> </script>
asp.net的大部分验证都是通过这个文件进行的，下面我就以一个最简单的必入项验证控件来说明一下：
第一步：
当进入页面时首先赋值：var Page_Validators = new Array(document.getElementById("RequiredFieldValidator1"));
然后会根据这个变量的值遍历进行验证，
接着调用ValidatorOnLoad方法，然后在这个方法中调用ValidatorHookupControlID，ValidatorHookupControl，ValidatorHookupEvent
最主要是在ValidatorHookupEvent中给控件加载事件
eval("control." + eventType + " = func;");
比如onblue，onkeypress，onchange等事件
接下来根据加载的事件当事件发生时调用对应的方法
第二步：
当用户输入时调用ValidatedTextBoxOnKeyPress，主要是用来判断用户是否输入了回车键，如果是的话触发验证
第三步：
当用户输入回车或者离开焦点时调用以下方法进行验证：
ValidatorOnChange，ValidatorValidate，IsValidationGroupMatch，RequiredFieldValidatorEvaluateIsValid，ValidatorGetValue，
ValidatorTrim，ValidatorUpdateDisplay，ValidatorUpdateIsValid，AllValidatorsValid
主要就是根据用户的输入进行判断，决定是否显示错误信息：val.style.display = val.isvalid ? "none" : "inline";
附修改后的带有一个必入项验证的页面源码(将WebResource.axd文件中相应的方法都移到本页面了)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head><title>
无标题页
</title></head>
<body>
<form>
<div>
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwULLTE5MDkxNzgwODFkZKLnaM8iGUsgGiWldhYd7fCPmt6s" />
</div>
<div>
<input name="TextBox1" type="text" id="TextBox1" />
<span id="RequiredFieldValidator1" style="color:Red;display:none;">RequiredFieldValidator</span></div>
<script type="text/javascript">
<!--
//页面加载时执行的方法
var Page_ValidationVer = "125";
var Page_IsValid = true;
var Page_BlockSubmit = false;
var Page_InvalidControlToBeFocused = null;
function ValidatorOnLoad() 
{
if (typeof(Page_Validators) == "undefined")
return;
var i, val;
for (i = 0; i < Page_Validators.length; i++) {
val = Page_Validators[i];
if (typeof(val.evaluationfunction) == "string") {
eval("val.evaluationfunction = " + val.evaluationfunction + ";");
}
if (typeof(val.isvalid) == "string") {
if (val.isvalid == "False") {
val.isvalid = false;
Page_IsValid = false;
}
else {
val.isvalid = true;
}
} else {
val.isvalid = true;
}
if (typeof(val.enabled) == "string") {
val.enabled = (val.enabled != "False");
}
if (typeof(val.controltovalidate) == "string") {
ValidatorHookupControlID(val.controltovalidate, val);
}
if (typeof(val.controlhookup) == "string") {
ValidatorHookupControlID(val.controlhookup, val);
}
}
Page_ValidationActive = true;
}
function ValidatorHookupControlID(controlID, val) {
if (typeof(controlID) != "string") {
return;
}
var ctrl = document.getElementById(controlID);
if ((typeof(ctrl) != "undefined") && (ctrl != null)) {
ValidatorHookupControl(ctrl, val);
}
else {
val.isvalid = true;
val.enabled = false;
}
}
function ValidatorHookupControl(control, val) {
if (typeof(control.tagName) != "string") {
return;
}
if (control.tagName != "INPUT" && control.tagName != "TEXTAREA" && control.tagName != "SELECT") {
var i;
for (i = 0; i < control.childNodes.length; i++) {
ValidatorHookupControl(control.childNodes[i], val);
}
return;
}
else {
if (typeof(control.Validators) == "undefined") {
control.Validators = new Array;
var eventType;
if (control.type == "radio") {
eventType = "onclick";
} else {
eventType = "onchange";
if (typeof(val.focusOnError) == "string" && val.focusOnError == "t") {
ValidatorHookupEvent(control, "onblur", "ValidatedControlOnBlur(event); ");
}
}
ValidatorHookupEvent(control, eventType, "ValidatorOnChange(event); ");
if (control.type == "text" ||
control.type == "password" ||
control.type == "file") {
ValidatorHookupEvent(control, "onkeypress",
"if (!ValidatedTextBoxOnKeyPress(event)) { event.cancelBubble = true; if (event.stopPropagation) event.stopPropagation(); return false; } ");
}
}
control.Validators[control.Validators.length] = val;
}
}
function ValidatorHookupEvent(control, eventType, functionPrefix) {
var ev;
eval("ev = control." + eventType + ";");
if (typeof(ev) == "function") {
ev = ev.toString();
ev = ev.substring(ev.indexOf("{") + 1, ev.lastIndexOf("}"));
}
else {
ev = "";
}
var func;
if (navigator.appName.toLowerCase().indexOf('explorer') > -1) {
func = new Function(functionPrefix + " " + ev);
}
else {
func = new Function("event", functionPrefix + " " + ev);
}
eval("control." + eventType + " = func;");
}
//按键事件
function ValidatedTextBoxOnKeyPress(event) {
if (event.keyCode == 13) {
ValidatorOnChange(event);
var vals;
if ((typeof(event.srcElement) != "undefined") && (event.srcElement != null)) {
vals = event.srcElement.Validators;
}
else {
vals = event.target.Validators;
}
return AllValidatorsValid(vals);
}
return true;
}
//离开焦点依次执行以下方法
function ValidatorOnChange(event) {
if (!event) {
event = window.event;
}
Page_InvalidControlToBeFocused = null;
var targetedControl;
if ((typeof(event.srcElement) != "undefined") && (event.srcElement != null)) {
targetedControl = event.srcElement;
}
else {
targetedControl = event.target;
}
var vals;
if (typeof(targetedControl.Validators) != "undefined") {
vals = targetedControl.Validators;
}
else {
if (targetedControl.tagName.toLowerCase() == "label") {
targetedControl = document.getElementById(targetedControl.htmlFor);
vals = targetedControl.Validators;
}
}
var i;
for (i = 0; i < vals.length; i++) {
ValidatorValidate(vals[i], null, event);
}
ValidatorUpdateIsValid();
}
function ValidatorValidate(val, validationGroup, event) {
val.isvalid = true;
if ((typeof(val.enabled) == "undefined" || val.enabled != false) && IsValidationGroupMatch(val, validationGroup)) {
if (typeof(val.evaluationfunction) == "function") {
val.isvalid = val.evaluationfunction(val);
if (!val.isvalid && Page_InvalidControlToBeFocused == null &&
typeof(val.focusOnError) == "string" && val.focusOnError == "t") {
ValidatorSetFocus(val, event);
}
}
}
ValidatorUpdateDisplay(val);
}
function IsValidationGroupMatch(control, validationGroup) {
if ((typeof(validationGroup) == "undefined") || (validationGroup == null)) {
return true;
}
var controlGroup = "";
if (typeof(control.validationGroup) == "string") {
controlGroup = control.validationGroup;
}
return (controlGroup == validationGroup);
}
function RequiredFieldValidatorEvaluateIsValid(val) {
return (ValidatorTrim(ValidatorGetValue(val.controltovalidate)) != ValidatorTrim(val.initialvalue))
}
function ValidatorGetValue(id) {
var control;
control = document.getElementById(id);
if (typeof(control.value) == "string") {
return control.value;
}
return ValidatorGetValueRecursive(control);
}
function ValidatorTrim(s) {
var m = s.match(/^\s*(\S+(\s+\S+)*)\s*$/);
return (m == null) ? "" : m[1];
}
function ValidatorUpdateDisplay(val) {
if (typeof(val.display) == "string") {
if (val.display == "None") {