1.网页上的TextBox并没有设AutoPostBack为true，为什么它能够执行事件处理程序？
2.我在Default.aspx页面如果点右键选“在浏览器中查看”，在出现的页面上操作一切
正常；如果通过按F5启动调试，在出现的页面上操作，会出现异常。
异常位置在CallBackHelper类的HandleError的“hr.StatusCode = 200;”这里。
报出的异常信息：“服务器无法在已发送 HTTP 标头之后设置状态。”
为什么同样的代码不同的运行方式，执行的结果不一样呢？
以下为部分代码：
CallBackHelper类：
public class CallBackHelper
{
private CallBackHelper() { }
public static bool IsCallBack
{
get
{
HttpRequest hr = CallBackHelper.GetHttpRequest();
return hr.Params["IsCallBack"] != null;
}
}
public static void Write(string Text)
{
HttpResponse hr = CallBackHelper.GetHttpResponse();
hr.Clear();
hr.StatusCode = 200;
hr.StatusDescription = "OK";
hr.Write(Text);
hr.Flush();
hr.End();
}
public static void HandleError(Exception e)
{
HttpResponse hr = CallBackHelper.GetHttpResponse();
hr.Clear();
hr.StatusCode = 200;
hr.StatusDescription = "ERROR";
hr.Write(e.ToString());
hr.Flush();
hr.End();
}
private static HttpResponse GetHttpResponse()
{
HttpResponse hr = null;
try
{
hr = System.Web.HttpContext.Current.Response;
}
catch (NullReferenceException nre)
{
throw new Exception("CallBackHelper could not access current HttpResponse object", nre);
}
return hr;
}
private static HttpRequest GetHttpRequest()
{
HttpRequest hr = null;
try
{
hr = System.Web.HttpContext.Current.Request;
}
catch (NullReferenceException nre)
{
throw new Exception("CallBackHelper could not access current HttpRequest object", nre);
}
return hr;
}
}
CallBackObject.js文件：
function CallBackObject() {
this.XmlHttp = this.GetHttpObject();
}
CallBackObject.prototype.GetHttpObject = function() {
var xmlhttp;
/*@cc_on
@if (@_jscript_version >= 5)
try {
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
xmlhttp = false;
}
}
@else
xmlhttp = false;
@end
@*/
if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
try {
xmlhttp = new XMLHttpRequest();
} catch (e) {
xmlhttp = false;
}
}
return xmlhttp;
}
CallBackObject.prototype.DoCallBack = function(eventTarget, eventArgument) {
var theData = '';
var theform = document.forms[0];
var thePage = window.location.pathname + window.location.search;
var eName = '';
theData = '__EVENTTARGET=' + escape(eventTarget.split("$").join(":")) + '&';
theData += '__EVENTARGUMENT=' + eventArgument + '&';
theData += '__VIEWSTATE=' + escape(theform.__VIEWSTATE.value).replace(new RegExp('\\+', 'g'), '%2b') + '&';
theData += 'IsCallBack=true&';
for (var i = 0; i < theform.elements.length; i++) {
eName = theform.elements[i].name;
if (eName && eName != '') {
if (eName == '__EVENTTARGET' || eName == '__EVENTARGUMENT' || eName == '__VIEWSTATE') {
// Do Nothing
}
else {
theData = theData + escape(eName.split("$").join(":")) + '=' + theform.elements[i].value;
if (i != theform.elements.length - 1)
theData = theData + '&';
}
}
}
if (this.XmlHttp) {
if (this.XmlHttp.readyState == 4 || this.XmlHttp.readyState == 0) {
var oThis = this;
this.XmlHttp.open('POST', thePage, true);
this.XmlHttp.onreadystatechange = function() { oThis.ReadyStateChange(); };
this.XmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
this.XmlHttp.send(theData);
}
}
}
CallBackObject.prototype.AbortCallBack = function() {
if (this.XmlHttp)
this.XmlHttp.abort();
}
CallBackObject.prototype.OnLoading = function() {
// Loading
}
CallBackObject.prototype.OnLoaded = function() {
// Loaded
}
CallBackObject.prototype.OnInteractive = function() {
// Interactive
}
CallBackObject.prototype.OnComplete = function(responseText, responseXml) {
// Complete
}
CallBackObject.prototype.OnAbort = function() {
// Abort
}
CallBackObject.prototype.OnError = function(status, statusText) {
// Error
}
CallBackObject.prototype.ReadyStateChange = function() {
if (this.XmlHttp.readyState == 1) {
this.OnLoading();
}
else if (this.XmlHttp.readyState == 2) {
this.OnLoaded();
}
else if (this.XmlHttp.readyState == 3) {
this.OnInteractive();
}
else if (this.XmlHttp.readyState == 4) {
if (this.XmlHttp.status == 0)
this.OnAbort();
else if (this.XmlHttp.status == 200 && this.XmlHttp.statusText == "OK")
this.OnComplete(this.XmlHttp.responseText, this.XmlHttp.responseXML);
else
this.OnError(this.XmlHttp.status, this.XmlHttp.statusText, this.XmlHttp.responseText);
}
}
页面文件：
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title></title>
<script language="jscript" type="text/jscript" src="CallBackObject.js"></script>
<script language="jscript" type="text/jscript">
var Cbo = new CallBackObject();
Cbo.OnComplete = Cbo_Complete;
Cbo.OnError = Cbo_Error;
function CheckUsername(Username) {
var msg = document.getElementById('lblMessage');
if (Username.length > 0) {
Cbo.DoCallBack('tbUsername', '');
}
else {
Cbo.AbortCallBack();
msg.innerHTML = '';
}
}
function Cbo_Complete(responseText, responseXML) {
var msg = document.getElementById('lblMessage');
if (responseText == '0') {
msg.innerHTML = '用户名存在！';
msg.style.color = 'red';
}
else if (responseText == '1') {
msg.innerHTML = '用户名长度必须在3到15之间，且不包含字母、数字和下划线以外的字符！';
msg.style.color = 'red';
}
else if (responseText == "2") {
msg.innerHTML = '用户名不存在！';
msg.style.color = 'green';
}
else {
msg.innerHTML = '执行出现错误！';
msg.style.color = 'red';
}
}
function Cbo_Error(status, statusText, responseText) {
alert(responseText);
}
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:Label id="Label2" runat="server" Font-Names="黑体,Arial Black" Font-Bold="True" Font-Size="X-Large">基于AJAX的数据验证</asp:Label>
<hr>
<asp:Label id="Label1" runat="server">用户名：</asp:Label>
<asp:TextBox id="tbUsername" runat="server" onkeyup="CheckUsername(this.value)" ontextchanged="tbUsername_TextChanged"></asp:TextBox>
<br>
<asp:Label id="lblMessage" runat="server"></asp:Label>
<br>
<%--<asp:TextBox ID="TextBox1" runat="server"
AutoPostBack="True" ontextchanged="TextBox1_TextChanged"></asp:TextBox>--%>
</form>
</body>
</html>
与此页面对应的cs文件：
protected void Page_Load(object sender, EventArgs e)
{
}
protected void tbUsername_TextChanged(object sender, EventArgs e)
{
if (!CallBackHelper.IsCallBack)
return;
string strName = tbUsername.Text;
try
{
string strReturnCode;
if (!IsValidUsername(strName))
{
strReturnCode = "1";
}
else if (!IsUsernameExist(strName))
{
strReturnCode = "2";
}
else
{
strReturnCode = "0";
}
CallBackHelper.Write(strReturnCode);
}
catch (Exception ex)
{
CallBackHelper.HandleError(ex);
}
}
private bool IsUsernameExist(string strUsername)
{
bool bRet = false;
switch (strUsername.ToLower())
{
case "test":
case "tom":
case "jack":
case "ajax":
case "aspnet":
bRet = true;
break;
}
return bRet;
}
private bool IsValidUsername(string strUsername)
{
return (Regex.IsMatch(strUsername, @"^(\w{3,15})$"));
}
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
Response.Redirect("http://www.g.cn");
}
